Biomedical subjects

C L Gómez Dumm

Publications and source records attributed to C L Gómez Dumm.

At least 19 recordsLinked to original sources

PubMed2004

Islet neogenesis: an apparent key component of long-term pancreas adaptation to increased insulin demand.

This study aimed to determine the relative importance of different functional and morphological pancreatic changes induced by the chronic administration of a sucrose-rich diet (SRD) to maintain normal glucose homeostasis. Male Wistar rats were fed either sucrose (SRD) or starch (CD) for 6 and 12 months. At both periods, serum glucose and triacylglycerol levels were significantly higher (P<0.05; paired and unpaired Student's t-test) in SRD rats. Serum insulin levels were significantly lower in SRD only at 12 months. At 6 months, the insulin secretion dose-response curve in SRD rats showed a shift to the left that was no longer observed at 12 months, when SRD islets decreased their response to 16 mM glucose. At 6 months, SRD rats showed a significant increase in beta-cell volume density (Vvi) and islet cell replication rate, together with a decrease in beta-cell apoptotic rate. Changes were not detected in the percentage of PDX-1- and islet neogenesis associated protein (INGAP)-positive cells. Conversely, at 12 months, there was a significant decrease in beta-cell Vvi and in the percentage of PDX-1-positive cells; the islet cell replication rate was not modified, and the number of apoptotic beta-cells increased significantly. No signs of increased neogenesis or INGAP-positive cells were recorded at any period in SRD rats. Our results show that SRD rats are unable to develop functional and morphological pancreatic reactive changes sufficient to maintain normal glucose and triacylglycerol levels for a long period. Such failure could be ascribed to their inability to increase the rate of neogenesis and of INGAP production.

Adaptation, Physiological↗

PubMed2002

Mechanisms involved in the beta-cell mass increase induced by chronic sucrose feeding to normal rats.

The aim of the present study was to clarify the mechanisms by which a sucrose-rich diet (SRD) produces an increase in the pancreatic beta-cell mass in the rat. Normal Wistar rats were fed for 30 weeks either an SRD (SRD rats; 63% wt/wt), or the same diet but with starch instead of sucrose in the same proportion (CD rats). We studied body weight, serum glucose and triacylglycerol levels, endocrine tissue and beta-cell mass, beta-cell replication rate (proliferating cell nuclear antigen; PCNA), islet neogenesis (cytokeratin immunostaining) and beta-cell apoptosis (propidium iodide). Body weight (g) recorded in the SRD rats was significantly (P<0.05) larger than that of the CD group (556.0+/-8.3 vs 470.0+/-13.1). Both serum glucose and triacylglycerol levels (mmol/l) were also significantly higher (P<0.05) in SRD than in CD rats (serum glucose, 8.11+/-0.14 vs 6.62+/-0.17; triacylglycerol, 1.57+/-0.18 vs 0.47+/-0.04). The number of pancreatic islets per unit area increased significantly (P<0.05) in SRD rats (3.29+/-0.1 vs 2.01+/-0.2). A significant increment (2.6 times) in the mass of endocrine tissue was detected in SRD animals, mainly due to an increase in the beta-cell mass (P=0.0025). The islet cell replication rate, measured as the percentage of PCNA-labelled beta cells increased 6.8 times in SRD rats (P<0.03). The number of apoptotic cells in the endocrine pancreas decreased significantly (three times) in the SRD animals (P=0.03). The cytokeratin-positive area did not show significant differences between CD and SRD rats. The increase of beta-cell mass induced by SRD was accomplished by an enhanced replication of beta cells together with a decrease in the rate of beta-cell apoptosis, without any evident participation of islet neogenesis. This pancreatic reaction was unable to maintain serum glucose levels of these rats at the level measured in CD animals.

Animals↗

PubMed2001

Altered functional responses with preserved morphology of gonadotrophic cells in congenitally athymic mice.

Neonatal thymectomy or congenital absence of the thymus induces severe reproductive deficiencies in female mice, which are associated with reduced levels of circulating and pituitary gonadotropins. In contrast, the reproductive function is well preserved in nude males. It was therefore of interest to assess gonadotrophic cell morphology and function in congenitally athymic male mice. Circulating gonadotropins were measured under basal and stressful conditions, taking as a reference their haired counterparts. Adult normal (+/+), heterozygous nude (nu/+), and homozygous (nu/nu) CD-1 mice were subjected to 1-h immobilization stress. Serum levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were assessed by RIA at 0, 30, and 60 min poststress. Athymic animals showed significantly lower basal levels of serum LH and FSH than their heterozygous littermates. Immunohistochemical assessment of LH and FSH cell populations revealed a normal morphology and cell number in the athymic animals compared to their normal littermates. Immobilization stress induced a significant reduction in gonadotrophin levels, particularly LH, in normal mice but had only a weak effect in athymic animals. It is concluded that congenital athymia in the adult male mouse is associated with decreased basal levels of serum LH and FSH, in the presence of a normal gonadotroph number and morphology. The anomalous responses of athymic mice to stress do not appear to be due to primary hypopituitarism but, rather, to an altered modulation of pituitary hormone secretion. .

Animals↗

PubMed2001

Effect of undernutrition on cranial components and somatotroph-lactotroph pituitary populations in the squirrel monkey (Saimiri sciureus boliviensis).

The aim of the present study was to investigate in monkeys the effects of undernutrition on neurocranial and facial components, correlated with a histometric and ultrastructural analysis of somatotroph (growth hormone, GH) and lactotroph (prolactin, PRL) pituitary populations. Twenty Saimiri sciureus boliviensis (Cebidae) of both sexes were employed. The monkeys were born in captivity and when they reached 1 year of age, they were separated into two groups: control and undernourished animals. They were fed ad libitum a 20% and 10% protein diet, respectively. The monkeys were radiographed when they were 3 years old in order to measure the length, width and height of the anterior, middle and posterior components of the neurocranium, as well as those of the masticatory, respiratory and optic components of the face. The volumetric and morphometric indices were then calculated. After the sacrifice, pituitary glands were processed for light and electron microscopy. The quantitative immunohistochemistry revealed a decrease in the volume density and cell density of both GH and PRL cells from malnourished animals when compared to control ones. The ultrastructural study showed changes suggestive of cellular hyperfunction for both types of cells in the former experimental group. Under nutrition also affected the size of the cranial components, with males being more affected than females; brain weight was, however, nonmodified by stress, with the brain/body ratio difference being the same for both sexes. We conclude that in monkeys, experimental undernutrition produces a decrease in the pituitary GH and PRL cell populations, in some way related to changes in the cranio-facial morphometric patterns.

Animals↗

PubMed2001

Ultrastructural and quantitative immunohistochemical changes induced by nonsteroid antiandrogens on pituitary gonadotroph population of prepubertal male rats.

Specific blockade of the androgen receptor by the nonsteroid antiandrogens flutamide and Casodex has proven to be a useful tool for studying androgens in vivo. The aim of the present study was to investigate the effect of antiandrogen administration at the pituitary level by evaluating the ultrastructural changes in gonadotrophs, in correlation with the quantitative immunohistochemical findings, and by comparing these alterations with the effect of androgen deprivation by castration either with or without subsequent androgen replacement. Male Sprague-Dawley rats (23 days old) were grouped as follows: (1) controls, (2) flutamide-injected (10 mg/rat/day), (3) Casodex-injected (10 mg/rat/day), (4) castrated, and (5) castrated plus androgen-replaced (dihydrotestosterone propionate; 40 microg/rat/day). Groups were sacrificed after 10 days of maintenance under each condition. Pituitaries were processed for both light and electron microscopy. Serial sections (4 microm) were obtained at different levels and immunostained by means of the primary murine monoclonal antibodies anti-FSH and anti-LH and a peroxidase-mediated EnVision System (Dako). Volume density, cell density and mean cell area were measured with an image analysis system (Imaging Technology, Software Optimas 5.2). The mean cell area (p < 0.001) and the volume density (p < 0.05) increased significantly in the flutamide- and Casodex-treated groups as well as the castrated group of FSH and LH cells. On the other hand, androgen replacement in the castrated rats, however, reduced in both parameters related to control animals. The cell density of FSH-secreting cells was increased (p < 0.05) in the Casodex and flutamide treatment as well as castrated group. The cell density of LH-secreting cells was augmented (p < 0.05) in the Casodex-treated group, while there was no increase in such parameter with flutamide and castration. The ultrastructure of all groups showed two types of gonadotrophs. Type I cells contained large (300-500 nm) and small (150-200 nm) secretory granules, while type II cells were smaller, and exhibited only small granules (100-200 nm). Flutamide-treated, Casodex-treated and castrated groups presented a decreased number of secretory granules with some exocytotic profiles, well-developed rough endoplasmic reticulum and an expanded Golgi complex of both types of cells. The gonadotrophs from the castrated group exhibited numerous mitochondria with electron-dense ring-shaped laminar figures, while in the castrated plus androgen-replaced rats only a few mitochondria had similar changes to those observed in castrated animals, as a possible residual alteration. Finally, the gonadotrophs from flutamide-treated rats showed mitochondrial alterations with clear areas and isolated electron-dense laminar figures. In summary, we conclude that lack of androgen reaction through the effects of nonsteroid antiandrogens and castration on prepubertal rats produced a hypertrophia-hyperplasia of the FSH cells, and hypertrophia of LH-secreting cells, with marked alterations at the ultrastructural level suggestive of a hyperstimulation stage.

Androgen Antagonists↗

PubMed2001

Morphometric and ultrastructural analysis of different pituitary cell populations in undernourished monkeys.

Undernutrition elicited by a low-protein diet determines a marked reduction of hypophyseal activity and affects the function of the respective target organs. The objective of the present investigation was to study the ultrastructural and quantitative immunohistochemical changes of the different pituitary cell populations in undernourished monkeys that had been previously shown to have significant changes in craniofacial growth. Twenty Saimiri sciureus boliviensis monkeys of both sexes were used. The animals were born in captivity and were separated into two groups at one year of age, i.e., control and undernourished animals. The monkeys were fed ad libitum a 20% (control group) and a 10% (experimental group) protein diet for two years. Pituitaries were processed for light and electron microscopy. The former was immunolabeled with anti-GH, -PRL, -LH, -FSH, -ACTH, and -TSH sera. Volume density and cell density were measured using an image analyzer. Quantitative immunohistochemistry revealed a decrease in these parameters with regard to somatotrophs, lactotrophs, gonadotrophs and thyrotrophs from undernourished animals compared to control ones. In these populations, the ultrastructural study showed changes suggesting compensatory hyperfunction. On the contrary, no significant changes were found in the morphometric parameters or the ultrastructure of the corticotroph population. We conclude that in undernourished monkeys the somatotroph, lactotroph, gonadotroph, and thyrotroph cell populations showed quantitative immunohistochemical changes that can be correlated with ultrastructural findings.

Animals↗

PubMed2000

Immunohistochemical and ultrastructural study of pituitary folliculostellate cells during aging in rats.

The impact of aging on pituitary folliculostellate (FS) cells is not well known. The aim of the work reported here was to carry out a quantitative immunohistochemical assessment of the FS population in male and female rats during aging and to correlate the findings with possible changes at the ultrastructural level. Young (4 months), old (20 months) and senescent (29 months) Sprague-Dawley rats of both sexes were sacrificed by rapid decapitation, their pituitaries dissected and processed by both light immunohistochemistry and electron microscopy. Serial sections (4 microm) were obtained at different levels and immunostained by means of rabbit anti-S100 serum as the primary antibody and a peroxidase-mediated EnVision System (Dako). Measurement of volume density (VD) and cell density (CD) was made in S100-reacting elements by means of an image analysis system (Imaging Technology, Optimas). These parameters were found to be significantly (p < 0.05) decreased in old and senescent rats as compared to young animals. In senescent females, which presented a high incidence of microprolactinomas, a significant (p < 0.01) increment of VD and CD was observed in FS cells in the area surrounding the adenomas, together with a marked decrease in those parameters within the tumors. Sexual dimorphism was not found except for the prolactinoma-bearing female group. The ultrastructure of FS cells showed the typical characteristics previously described in the pituitary gland. Only moderate changes in the endoplasmic reticulum were observed in old and senescent animals. We conclude that aging has a clear effect on the morphology of the pituitary FS cell population.

Aging↗

PubMed2000

Quantitative ultrastructural changes induced by sucrose administration in the pancreatic B cells of normal hamsters.

We have previously reported that young male Syrian hamsters receiving a sucrose-rich diet presented increased B-cell replication rate and size. The aim of the present study was to analyze, under the same experimental conditions, the ultrastructural changes in B cells. For this purpose, young male Syrian hamsters were fed with a commercial diet and 10% sucrose in their drinking water (S group) while the control group (C) received the same diet and tap water, for 5 weeks. Samples of the pancreas removed after that period were processed for the immunohistochemical identification of B cells as well as for measuring several ultrastructural parameters. S hamsters showed higher serum insulin levels, while similar serum glucose values were obtained in animals from both groups. The B cells from S group exhibited lesser number of dense secretory granules at expenses of an increase of the pale ones, increased number of both exocytosis profiles and fusion-granule images, as well as enlargement of the intercellular space and mitochondrial area. Marked expansions of this space, limited by junctional complexes, were observed between adjacent B cells. These results would indicate that sucrose administration to normal hamsters not only increases the pancreatic B-cell mass but also induces measurable subcellular changes in the individual B-cell characteristic of an enhanced secretory activity. The present model would represent a useful tool for testing strategies in preventing the damage or promoting the recovery of the pancreatic B cells.

Animals↗

PubMed1999

Hormone coexpression in the adult toad endocrine pancreas: double-label immunofluorescence under basal conditions and after glucose injection.

We have investigated the type and frequency of hormone coexpression in the endocrine pancreas of amphibians both under basal conditions and after sustained glucose loading. Adult male specimens of the wild toad Bufo arenarum were injected with a 50% (w/v) glucose solution (2 g/100 g) for 2 days, while control animals received an equal volume of the vehicle. Serum glucose levels were measured at the time of sacrifice and the pancreatic free lobe was processed for light microscopy. A double-labeling immunofluorescence study was performed for the detection of insulin (I), glucagon (G), somatostatin (S), and pancreatic polypeptide (PP). Heterospecific antisera against the following hormone combinations were used for their detection and immunocytochemical localization: I+G, I+PP, G+PP, S+G, and S+PP; visualization of the reacted IgG's was effected by fluorescein- and rhodamine-conjugated species-specific antibodies as fluorophores. Intracellular hormone coexpression was found to occur in the combinations G+PP, S+G, and S+PP. Moreover, glucose administration caused, together with a marked hyperglycemia (123 +/- 17 vs 23 +/- 1 mg/dl; P < 0.05), a decrease in the fraction of cells containing both G and PP together (from 106.3 +/- 8.1 to 26 +/- 4 cell/mm2) along with a reciprocal rise in the number of cells possessing G alone (from 128.7-152.3 to 235.9-274 cell/mm2). The fewer number of cells coexpressing either of the other two hormone combinations, however, were unaffected by glucose injection. With respect to the simultaneous measurement of I+G and I+PP, no cells were detected with both hormones of either pair, and the I-containing cells were more frequent in each instance in the control toads (264.8 +/- 22.3 to 269.2 +/- 27 cell/mm2). For both combinations, however, this value diminished significantly in the glucose-treated animals (108 +/- 2 cell/mm2 for I+G and 112.1 +/- 7. 8 cell/mm2 for I+PP). While the G-containing cells became more numerous (rising to 235.9 +/- 12.4, 274 +/- 26, and 250.4 +/- 23.7 cell/mm2 for I-G, G-PP, and G-S combinations, respectively), the PP- and S-containing cells remained unaffected. We conclude that the copresence of different hormones within the same cell is a relatively common finding in the non-I-secreting elements of the adult toad pancreas and that the proportions of specific cell types are affected by glucose administration. We thus propose that intracellular hormonal coexpression in this fashion may well represent a rapid and efficient regulatory mechanism for compensating for the metabolic stress imposed by glucose loading.

Animals↗

PubMed1999

Tyrosine phosphorylation and morphological transformation induced by four vanadium compounds on MC3T3E1 cells.

The present study was performed to determine the phosphotyrosine-protein levels induced by insulin and by four vanadium derivatives in MC3T3E1 osteoblast-like cells. We have also attempted to associate these patterns with the vanadium-induced growth and morphological changes of such cells. Vanadate (Vi), vanadyl (VO), bis(maltolato)oxovanadium (IV) (BMOV) and bis(maltolato)dioxovanadium (V) (BMV) stimulate cell growth in a narrow range of concentration, but are also inhibitors for the cells at high concentrations. Vanadium-treated cells displayed clear changes in their morphology after overnight incubation. However, BMV was the least cytotoxic and the weakest inducer of morphological changes. All the compounds promote the phosphorylation of tyrosine residues in several proteins. This effect was more pronounced at low than at high doses. At low doses (10 microM), BMV showed a phosphorylation pattern similar to that of insulin, while Vi, VO and BMOV induced strong phosphorylation of cell proteins. The present findings suggest that the vanadium-induced growth regulation and morphological changes in MC3T3E1 osteoblast-like cells are associated with the ability of these agents to increase the phosphotyrosine protein levels and to inhibit phosphotyrosine phosphatases. These properties are dependent on the oxidation state as well as on the organic ligand which coordinates the vanadium atom.

3T3 Cells↗

PubMed1999

Effects of androgens and antiandrogens on the quantitative immunohistochemistry of gonadotrope cells in prepubertal male rats.

In the male rat, androgens are involved in the feedback regulation of gonadotropin synthesis and secretion. Specific androgen-receptor blockade by the nonsteroidal antiandrogens, flutamide and Casodex, has proven to be a valid tool for studying androgen effects in vivo. The aim of the present study was to investigate the effect of antiandrogen administration at the pituitary level by evaluating the changes in gonadotropes through quantitative immunohistochemistry, and by comparing these alterations with the effect of androgen deprivation by castration either with or without subsequent androgen replacement. Male Sprague-Dawley rats (23 days old) were randomly divided into 5 groups for the following treatments: (a) controls; (b) flutamide-injected (10 mg/rat/day in a gelatin vehicle); (c) Casodex-injected (10 mg/rat/day in an oil vehicle); (d) castrated, and (e) castrated and dihydrotestosterone propionate-replaced (40 microg/rat/day in an oil vehicle). Groups were then sacrificed after 10 days of maintenance under each condition. Pituitaries were fixed in Bouin's fluid and embedded in paraffin. Serial sections (4 micrometer) were obtained at different levels and immunostained by means of the primary murine monoclonal antibodies anti-FSH and anti-LH and a peroxidase-mediated EnVision System (Dako). Measurements of volume density (VD) and individual mean cell area were made by means of an image-analysis system (Imaging Technology, Optimas). Serum FSH and LH levels were determined by radioimmunoassay (RIA). Serum gonadotropin levels, VD, and mean cell area increased significantly in the flutamide-treated, Casodex-treated, and castrated groups (p < 0.05). Androgen replacement in the castrated rats, however, reduced VD, mean cell area, and serum gonadotropins to levels comparable to those of controls. We conclude that either androgen blockade by antiandrogens or castration produce an enhancement in the gonadotrope cell population in prepubertal rats, as shown by an increase in both VD and mean cell area, as well as an elevation in FSH- and LH-immunoreactive cells. These observations correlate well with the changes found in the levels of circulating gonadotropins as measured by RIA.

Androgen Antagonists↗

PubMed1998

Immunohistochemical and ultrastructural age-related changes in rat lactotroph cells.

Ageing produces alterations in some functions of the hypothalamo-pituitary axis leading to sexually dimorphic changes in the prolactin (PRL)-secreting cells. Since quantitative morphological data of these age-associated alterations are scarce, we carried out a morphometric immunohistochemical assessment as well as an ultrastructural study of the PRL cell population in male and female rats of different ages. Young (3-month-old), old (20-month-old), and senescent (31-month-old) Sprague-Dawley rats of both sexes were sacrificed by rapid decapitation, their pituitaries immediately dissected out and processed for both immunohistochemistry and electron microscopy. Analysis of different morphometric parameters revealed that the cell density (CD) and volume density (VD) significantly decreased with age in male rats. In females, while CD showed a significant age-related diminution when young rats were compared to old ones, this parameter increased in senescent animals. The VD presented higher values in senescent rats. When the data were compared between sexes, VD was found to be higher in females if old and senescent rats were considered. Finally, CD increased significantly in females when compared to males. The ultrastructure of the PRL cells from old and senescent animals of both sexes exhibited changes suggestive of an hyperstimulation state, with some prolactotrophs having the appearance of cells undergoing an involutive process. We conclude that ageing has a differential impact on the PRL cells of male and female rats with respect to the immunohistochemical and ultrastructural features of that cell population.

Aging↗

PubMed1997

Bilateral adrenal enucleation-induced changes in adenohypophyseal pro-opiomelanocortin (POMC)-related peptides synthesis and secretion: a comparative study with adrenalectomized rats.

The aim of the present study was to elucidate the modulatory effect of transient changes in endogenous glucocorticoids, occurring after bilateral adrenal enucleation (ENUC), on anterior pituitary (AP) proopiomelanocortin (POMC)-derived peptides synthesis and output in rats. For this purpose, adult female rats were either bilaterally ENUC, adrenalectomized (ADX), or sham-operated (SHAM) and killed by decapitation 2, 7, 14, and 21 days after surgery. Trunk blood was collected for measurements of ACTH, beta-endorphin (beta-END) and corticosterone (B) concentrations; APs were quickly dissected for the determination of ACTH, beta-endorphin (beta-END)-like (beta-END-LI) and gamma 3-MSH contents and adrenal glands were removed and submitted to histological study. The results indicate that ENUC and ADX increased AP POMC-related peptides synthesis and release in association with changes in the AP processing of peptides belonging to the N-terminal (gamma 3-MSH), mid (ACTH) and C-terminal (beta-LPH/ENDs) portions of POMC. While ADX abolished plasma B levels, ENUC induced a transient (day 2) decrease in plasma B concentrations which returned to SHAM levels at 7 days after surgery. These data tallied with the histological observations carried out, indicating a time-dependent regenerative process of the adrenal which was completed by three weeks after ENUC. There was a different pattern in plasma ACTH and beta-END levels between ENUC and ADX; maximal plasma peptide levels were found 7-14 days after ENUC, then falling down to SHAM values at 21 days post ENUC. Conversely, there was a constant increment in plasma peptide levels up to 21 days after ADX. At 2 days after both ENUC and ADX all peptides measured in the AP were lower than SHAM values, thus reflecting a rapid corticotrope secretion. Thereafter, 7 or more days after surgery, AP peptide content in ADX rats increased, in a time-related fashion, up to 21 days after surgery. Only beta-END-LI showed a similar AP content to that of the SHAM group, thereafter indicating a preferential cleavage of POMC to beta-END long after ADX (21 days). ENUC rats showed increased AP POMC peptides content throughout the whole time, and it was significantly different from SHAM and ADX values 14 days post-surgery. Interestingly, we found an increment in AP gamma 3-MSH, a peptide which is preferentially synthesized in the intermediate lobe of the rat pituitary, in both ENUC and ADX situations. Our results further indicate that: 1) glucocorticoids, from regenerating adrenal origin, induce a fast negative feedback mechanism on AP secretion, and 2) there might be a delayed inhibitory action of newly synthesized corticosteroids on higher levels of the central nervous system. The lack of glucocorticoids (ADX) clearly corroborates a persistent enhancement of AP POMC-related peptides synthesis and secretion. The differences in AP processing of POMC between ENUC and ADX might be due to qualitative/quantitative changes in hypothalamic ACTH secretagogues output.

Adrenal Glands↗

PubMed1997

Sexual dimorphism in the age changes of the pituitary lactotrophs in rats.

It is known that aging is associated with alterations in hypothalamic and pituitary functions. In the present study, we have undertaken a quantitative immunohistochemical assessment of the lactotroph cell population as well as prolactin (PRL) secretion, in male and female rats of different ages. Pituitaries from young (3 months), old (20 months) and senescent (29 months) male and female Sprague-Dawley rats were processed for the immunohistochemical detection of lactotrophs. Serum PRL was measured by a homologous RIA. Additionally, the in vitro PRL secretory activity was estimated by perifusion of pituitary cells from senescent animals. Analysis of morphometric parameters revealed age-related changes of PRL cell population in animals of both sexes. The cell density (CD), surface density (SD) and volume density (VD) decreased with age in both male and female rats. However, CD as well as SD appeared to have increased in females when compared to males, either in young or old animals, while VD was higher only in old females. The pituitaries of senescent females displayed chromophobic microadenomas on a background of diffuse PRL cell hyperplasia. Prolactin serum levels showed a marked increase with age in females, but only a modest elevation in males. In senescent females, PRL production per cell was reduced. We conclude that in rats, there exists a clear sexual dimorphism in the age-related changes of pituitary PRL cells.

Aging↗

PubMed1997

Postnatal sequential changes in islet morphology and insulin secretion of normal hamsters.

We have studied the postnatal development of the endocrine pancreas from normal female Syrian golden hamsters 1, 8, and 24 weeks of age. The observations were made by (a) analysis of insulin secretion in response to glucose using isolated pancreatic islets and (b) identification and quantitation of insulin-, glucagon-, somatostatin-, and pancreatic polypeptide-secreting cells. Glucose-induced insulin secretion showed typical dose-response curves. However, whereas in 24-week-old animals maximal secretion was already present with 8 mM glucose, in younger hamsters such a response was attained only with 20 mM glucose. The volume density of the endocrine pancreas and the number of islets were increased in 1-week-old hamsters compared to the older animals. The islet volume average in 8-week-old hamsters was almost three times higher than that measured in 1-week-old animals. However, the proportion and size of each cell type in the islets did not present significant differences among the groups studied. Our results show that, in hamsters, the endocrine pancreas reaches the adult general characteristics late after birth. Furthermore, the definite morphological pattern is attained far earlier than the secretory response. These observations provide basic information for further studies regarding the mechanisms and factors that control both the growth and the differentiation of endocrine cell populations as well as glucose-induced insulin secretion in a simple experimental model.

Age Factors↗

PubMed1996

Topographic differences in cell populations and insulin secretion in the endocrine pancreas of the toad Bufo arenarum.

We analyzed the endocrine cell topography within the amphibian pancreas and the relationship of this distribution to lobular variation in insulin content and secretion. Pancreases from adult male toad Bufo arenarum were separated into their five lobes: free, gastric, hepatic, duodenal, and jejunal. Pieces of each lobe were incubated with glucose, arginine, and K+ and the insulin concentration in the medium was measured by radioimmunoassay. In the presence of 2 or 8 mM glucose, 10 mM arginine, and 10 mM K+ the free lobe released a significantly greater amount of insulin than the other lobes, while the output of the gastric lobe was greater than that of the duodenal, hepatic, and jejunal. At 8 mM glucose, every pancreatic lobe released a significantly higher amount of insulin than at 2 mM. The insulin content of the free lobe was significantly higher than that of the others, whereas this parameter was comparable among the latter. These pancreases contained islets of variable size and irregular shape. B and non-B cells, detected by immunoperoxidase staining, were located at the central and peripheral zones of the islets, respectively. A large number of non-B cells were also scattered over the exocrine component. Morphometrical analyses revealed the following sequence of endocrine cell percentage: free lobe > gastric lobe = duodenal lobe > jejunal lobe = hepatic lobe. Some 48% of the endocrine cells were present in the islets, while the remaining 52% were found throughout the exocrine pancreas. In the free lobe, more endocrine cells were located within the islets (65%) than outside and in the gastric lobe the proportion was almost equal (48% within, 52% outside), but in the hepatic, duodenal, and jejunal lobes the majority lay outside the islets (61, 63, and 70% extrainsular, respectively). The area covered by B and D cells was far larger within the islets than outside, with the relative magnitude of this difference being free lobe > gastric lobe > duodenal lobe > hepatic lobe = jejunal lobe. In the free lobe, this relative distribution was more skewed than in the remaining lobes. PP and A cells occupied a more extensive area outside the islets than inside in every lobe. There were no significant differences among the extrainsular areas occupied by each type of endocrine cell within a given pancreatic lobe. These results constitute the first demonstration of the heterogeneity in morphology, insulin content, and secretory function among the pancreatic lobes in B. arenarum. The data further suggest that the nonuniform secretory capacities of amphibian pancreatic lobes reflect localized differences in their insulin content, which heterogeneity in turn stems from the dissimilar distribution and organization of their constituent endocrine-cell populations.

Animals↗

PubMed1996

[Structure and ultrastructure of the endocrine pancreas in diabetic transgenic mice].

The aim of the present study was to confirm the structural changes and to establish the ultrastructural alterations that occur in the endocrine pancreas of mice with an induced insulin-dependent diabetes mellitus (IDDM) syndrome. For that purpose, we used transgenic mice (OVE 27) that overexpress a calmodulin gene in the beta cells of the endocrine pancreas. In these animals, the excess of calmodulin decreases the cytosolic calcium levels in beta cells, leading to morphological and functional alterations that produce a severe IDDM. Sections of pancreas (tail) from 4 male 5-week-old diabetic mice (glycemia: 376 +/- 2 mg/dl) and from 4 normal age-matched males (glycemia: 113 +/- 13 mg/dl) were processed. Light microscopic immunohistochemical observations confirmed a decrease in the number and size of pancreatic islets in transgenic mice, together with a disruption in their architecture, without an associated inflammatory response. The ultrastructural studies revealed diverse degrees of injury in the beta cells, such as the presence of membrane interdigitations and alterations in their organelles and secretory granules. These findings are in agreement with the quantitative and functional impairment of beta cells, coexisting with a normal appearance of non-beta cell populations within the pancreatic islets. Our results demonstrate the existence of ultrastructural changes in the pancreatic beta cells of the experimental model studied. Such changes, together with the immunohistochemical alterations previously described, contribute to explain the appearance of a diabetic syndrome in these animals.

Animals↗

PubMed1995

Quantitative immunohistochemical changes in the endocrine pancreas of nonobese diabetic (NOD) mice.

The nonobese diabetic (NOD) mouse is an animal model that shares a number of clinical, genetic, and immunologic characteristics with human insulin-dependent diabetes mellitus. Since little is known about the morphometric cell profiles in the endocrine pancreas of these NOD animals, it was of interest to assess their changes in morphometry within the pancreatic islet cell types during two stages of this syndrome. Prediabetic (6-week-old) and diabetic (16-week-old) NOD female mice, as well as normal C57BL/6 female mice (15 weeks old), were used. Light microscopic immunocytochemical and morphometric methods were employed to study the endocrine cell populations. The immunoperoxidase technique for the identification of insulin, glucagon, somatostatin, and pancreatic polypeptide, as well as the point-counting method, was used on serial sections of pancreas tissue. Compared to those of normal and prediabetic mice, pancreata from diabetic animals showed a decrease in both the number of islets and the volume density of the endocrine component. Analysis of islet tissue revealed a significant diminution of B-cell volume density, as well as an increased A-, D-, and PP-cell volume density. A parallel variation in the number of B and non-B cells was also found. In addition, when the total pancreatic tissue surface was taken as reference, the fractional area occupied by all the different types of islet cells was seen to be diminished in a variable fashion. We conclude that the diabetic syndrome of NOD mice not only severely affects the B-cell mass, but also causes marked changes in the non-B endocrine-cell populations.

Animals↗