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C Remacle

Publications and source records attributed to C Remacle.

At least 73 records · Page 4Linked to original sources
PubMed1991

The influence of gamma-aminobutyric acid on hormone release by the mouse and rat endocrine pancreas.

The present study was aimed at localizing gamma-aminobutyric acid (GABA) and its enzyme of synthesis, glutamic acid decarboxylase (GAD), in the mouse pancreas by immunocytochemical methods. The influence of GABA on hormone release was also studied with normal mouse and rat islets and the isolated perfused rat pancreas. Particular attention was paid to glucagon release to test a recent hypothesis suggesting that GABA mediates the still unexplained glucose-induced inhibition of glucagon release. GABA and GAD were identified only in islet cells and never in the exocrine tissue. Exogenous GABA, baclofen (agonist of GABAB receptors), muscimol (agonist of GABAA receptors), or bicuculline (antagonist of GABAA receptors) did not affect insulin and somatostatin release by isolated mouse or rat islets. GABA was also without effect on glucose-induced electrical activity in mouse B-cells. Glucagon secretion by mouse islets was only slightly inhibited (approximately 20%) by GABA. Since muscimol had a similar effect, and baclofen was ineffective, the inhibition by GABA probably involves GABAA receptor activation. Bicuculline, however, did not antagonize the inhibitory effects of GABA and muscimol, probably because the antagonist alone also decreased glucagon secretion. In contrast to GABA, low (3 mM) and high (20 mM) concentrations of glucose strongly inhibited (approximately 50-65%) glucagon release; this inhibition was not prevented by bicuculline. Similar results were obtained with the perfused rat pancreas; muscimol slightly inhibited glucagon release under various conditions, and bicuculline did not reverse the strong inhibition produced by 16.7 mM glucose. In conclusion, GABA does not affect insulin and somatostatin secretion, but inhibits A-cells, probably by acting on GABAA receptors. It is unlikely, however, that this small inhibitory effect can account for the inhibition of glucagon release produced by glucose.

Animals↗
PubMed1991

Islet function in offspring of mothers on low-protein diet during gestation.

A low-protein diet (8 vs. 20%) administered during pregnancy affects the structure and function of the endocrine pancreas of the offspring. At 21.5 days of gestation, we reported a reduction of cell proliferation, islet size, islet vascularization, and pancreatic insulin content. In this study, we demonstrated an impairment of insulin secretion of these fetal islets when stimulated in vitro with amino acids such as arginine and leucine. If the offspring is kept on the same low-protein diet during suckling, weaning, and adulthood, fasting insulin levels remain low in the presence of normal blood glucose levels. Glucose tolerance at 70 days is impaired, with lower insulin response. In addition, permanent functional damage seems to be induced in utero by a low-protein diet, because a normal diet given from birth to adulthood does not restore normal insulin response after a glucose challenge. Our experimental results stress the impact of a balanced diet with qualitative and quantitative amino acid composition for the fetal endocrine pancreas to develop normally, without lasting functional and structural consequences in adulthood.

Aging↗
PubMed1990

Mitochondrial genome transmission in Chlamydomonas diploids obtained by sexual crosses and artificial fusions: role of the mating type and of a 1 kb intron.

The linear mitochondrial DNAs of the two infertile algal species Chlamydomonas smithii and C. reinhardtii are co-linear with the exception of a 1 kb intron (alpha intron) located in the cytochrome b gene of C. smithii. C. smithii also possesses an additional HpaI restriction site (H marker) located in the COXI gene, about 5 kb from the intron. In reciprocal crosses, C. smithii (H+ alpha +) x C. reinhardtii (H- alpha -), the alpha intron is transmitted to all diploid progeny, whereas the H marker is frequently transmitted either biparentally or paternally depending on whether the C. smithii parent is maternal (mt+) or paternal (mt-). In diploids resulting from artificial fusion between vegetative cells, the absolute transmission of alpha is accompanied by the frequent transmission of the H+ marker, irrespective of the mating type of the parental strains. Finally, in reciprocal crosses between C. smithii (H+ alpha +) and recombinant H- alpha + clones, the transmission of the H marker is predominantly paternal or biparental. These results allow us to conclude that (1) the alpha intron behaves as a group I intron whose unidirectional conversion influences the transmission of the H marker; and (2) the mt- paternal mitochondrial genome is transmitted more often than the mt+. The mating type has no effect in diploids obtained by artificial fusion.

Chlamydomonas↗
PubMed1990

Immunocytochemical and autoradiographic studies of the endocrine cells interacting with GABA in the rat stomach.

There are now increasing evidences suggesting that GABA is able of direct interaction with certain endocrine cells. In the present study, highly specific anti-GABA-glutaraldehyde antibodies and 3H-GABA uptake were used at the light and electron microscope levels to investigate the occurrence of cells containing endogenous GABA or taking up exogenous GABA in the mucosal antrum and corpus of the rat stomach. Only certain endocrine cell types of both regions were immunostained or grain-labelled. However, the morphology of their secretory granules did not allow to identify the nature of their hormone with certainty but suggested that somatostatin-like cells could interact with GABA. The combination of gastrin and somatostatin immunodetection with 3H-GABA uptake autoradiography at the light microscope level, revealed that a subpopulation of somatostatin-like cells and other still unidentified endocrine cells are able to take up GABA, while the gastrin-like cells are not. These results reinforce the hypothesis that certain endocrine cell types of the diffuse endocrine system of the digestive tract are able to directly interact with GABA.

APUD Cells↗
PubMed1990

Morphologic characterization of osteoblast-like cell cultures isolated from newborn rat calvaria.

Two methods for harvesting osteoblast-like cell populations from newborn (10 days) rat calvaria were compared. The first one consisted in culturing the periosteum-free bones and then trypsinizing the cells on the bone surface. The second one involved the migration of the osteoblasts on glass fragments before trypsinization. Since the plating efficiency, the proportion of alkaline phosphatase-positive cells, the population doubling time, and the calcium deposition were more adequate, the second method was used to further characterize the behavior of the cultures. During the first week of culture, the cells featured shapes similar to those observed in vivo on the surface of periosteum-free calvaria. They formed multilayers and, in the presence of ascorbic acid, synthetized an organic matrix containing exclusively type I collagen. Later, small amounts of type III collagen appeared. The cells were embedded in the matrix and progressively acquired the morphologic phenotype of osteocyte-like cells. The matrix mineralized in the presence of beta-glycerophosphate. The technique of drop-inoculation (high concentration of cells in a small volume of medium) promoted the multilayer formation and the achievement of large mineralized plates (about 1 cm2) in 3 weeks of culture.

Alkaline Phosphatase↗
PubMed1990

Culture of endocrine pancreatic cells in protein-free, chemically defined media.

Cell suspensions prepared by collagenase digestion of pancreata obtained from 21.5-d-old rat fetuses were preincubated in RPMI medium containing 10% fetal bovine serum (FBS), to ensure cell adhesion. Twenty hours later, this medium was replaced by a chemically defined medium. Dulbecco's modified Eagle's (DME)-F12 was used alone or supplemented with various combinations of transferrin, sodium selenite, or Ultroser G. The evolution of the culture and the islet ultrastructure were similar in defined and serum-containing media. However, in the defined medium, the neoformed islets seemed less numerous, and the fibroblast layer less dense, when compared to the RPMI + 10% FBS control medium. At Day 7, in defined media, the total insulin content per dish was half that of control cultures. None of the tested additives improved the yield of the cultures. The fractional insulin release per day was elevated in defined media. In subsequent incubations, glucose and leucine stimulated insulin release in a way characteristic of these cells of fetal origin. The labeling index of islet cells cultured in DME-F12 reached 10.7%, which is not far from that observed in RPMI + 10% FBS. Such a defined medium is useful to study B cell physiology, avoiding the possible interaction of serum components with substances to be tested.

Animals↗
PubMed1990

The stroma-vascular fraction of rat inguinal and epididymal adipose tissue and the adipoconversion of fat cell precursors in primary culture.

The stroma-vascular fraction (SVF) of inguinal and epididymal fat pads of 4 week-old rats was studied by electron microscopy. Among the various cell types, endothelial cells and preadipocytes were found in both SVF, while mesothelial cells were only detected in the epididymal SVF. The resulting heterogeneity of primary culture and the adipoconversion of the fat cell precursors were studied in a serum-supplemented medium enriched with insulin (14.5 nM) and exogenous triglycerides. Despite the heterogeneity of the inoculum, the primary cultures were rather homogeneous, fat cell precursors being the main cell type. Distinctive contaminant fibroblast-like cells were observed in both cultures, whereas epithelial-like cells, which correspond most probably to mesothelial cells, were only found in epididymal cultures. Differentiation of fat cell precursors was assessed by the appearance of lipoprotein lipase (LPL) and glycerol-3-phosphate dehydrogenase (GPDH). LPL activity was found in the same level in cells of both deposits while GPDH activity was elevated in inguinal vs epididymal derived stroma-vascular cells. The different adipose conversion pattern of both cultures was confirmed by morphological quantification: the maturation of epididymal fat cell precursors was faster but less extensive. These differences could be related mainly to regional localization rather than to different maturation of the two fat deposits.

Adipose Tissue↗
PubMed1990

Effect of a low protein diet during pregnancy on the fetal rat endocrine pancreas.

The administration of a low protein (LP, 8% protein/dry matter) but isocaloric diet to gestating rats did not affect their fertility, but slightly reduced the quantity of food intake as well as body weight gain. The LP diet also did not affect the placental weight, but the weight of the offspring was decreased. Accordingly the fetal endocrine pancreas was altered by the LP diet. Two different morphometric analyses showed that in the LP neonate B-cell proliferation and islet size were reduced in the head of the pancreas. In the pancreatic tail, these parameters were also decreased but to a lesser extend. Islet vascularization in the neonates was dramatically reduced in both parts of the pancreas when the mothers were fed with the LP diet.

Animals↗
PubMed1989

The development of the fetal rat intestine and its reaction to maternal diabetes. I. Morphometrical analysis in normal conditions.

In rodents, the fetal intestine develops rapidly during the last 5 days of gestation. The present investigation describes the events which occur in the duodenum, jejunum and ileum of fetal Wistar rat from day 16.5 to 21.5. The first villi and microvilli as well as endocrine cells already appear at 17.5 days in the duodenal mucosae. Goblet cells are detected at 18.5 days. The structure of the intestinal mucosa at 21.5 days is similar to that of adults. The evolution was quantified by morphometric analysis. The external and inner circumference, the length of the villi profile and the increased absorption area due to the villi profile were measured. We demonstrated that the total enlargement of the luminal surface area due to the villi and the microvilli in the duodenum of the fetus at 21.5 days is similar to that in the adult duodenum. This morphometric analysis could be used to detect possible disturbances in the development of the fetal intestine.

Animals↗
PubMed1989

The development of the fetal rat intestine and its reaction to maternal diabetes. II. Effect of mild and severe maternal diabetes.

Diabetes during pregnancy induces specifically structural and functional changes in the fetal endocrine pancreas. Other organs are affected as well. In this study, the fetal intestinal tract which is in close connection with the endocrine pancreas was analysed during diabetic gestation. The disease was induced by two different doses of streptozotocin which led to a mild or severe diabetic state in the mother. In fetuses from mildly diabetic as well as from severely diabetic rats, the time sequence in the appearance of the differentiated cells was identical and similar to that of controls. However, morphometric analysis of the intestine of fetuses from severely diabetic rats revealed a decrease in each of the parameters measured which led to a general hypotrophy of the intestine. In the fetuses from mildly diabetic rats, the values of the morphometric parameters of the duodenal mucosa remained unchanged and comparable to those of the control group. The vascularisation of the duodenum is modified in these fetuses because the volume density of the blood vessels is significantly increased. In conclusion, both diabetic states of the mother induce various alterations in the fetal intestine, including the blood vessels. The nature of the structural changes observed in the intestine could lead to modifications in the function of the entero-pancreatic system in these fetuses.

Animals↗
PubMed1989

High-affinity GABA uptake in a subpopulation of somatostatin cells in rat pancreas.

The aim of this study was to localize the high-affinity uptake of [3H]-GABA in Langerhans islets of rats aged 2.5, 7.5, and 75 days. On high-resolution autoradiography, cells presenting characteristic somatostatin granules were labeled, whereas others containing similar granules appeared nearly devoid of silver grains. Immunogold detection with antisomatostatin antibodies and high-resolution autoradiography suggested that uptake of GABA is indeed performed by somatostatin cells. To test the heterogeneity of uptake frequency in somatostatin cells, a second approach, coupling immunohistochemistry with anti-somatostatin, anti-PP, anti-glucagon, anti-glicentin, and anti-CCK antibodies, and low-resolution autoradiography, was applied on paraffin sections. It demonstrated that the uptake ability is not characteristic of all the somatostatin cells but of only a subpopulation of them. A few cells not immunoreactive to the anti-somatostatin antiserum also appeared to be able to take up GABA. Moreover, except for a rare few, the PP-glucagon-, glicentin-, and CCK-39-immunoreactive cells were not labeled by autoradiography.

Animals↗
PubMed1989

Effects of stimulation of adenylate cyclase and protein kinase-C on cultured fetal rat B-cells.

To study the maturation of fetal pancreatic B-cells, cell suspensions of pancreas from 21.5-day-old fetuses were cultured in RPMI medium containing 10 mM glucose. Forskolin (1 microM), used to stimulate adenylate cyclase, moderately delayed the neoformation of islets, slightly accelerated the proliferation of endocrine cells, and considerably increased insulin release by the cultures. The latter increase was not completely compensated for by the stimulation of insulin biosynthesis, so that the islet insulin content was decreased. The phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA; 25 nM), used to stimulate protein kinase-C, had little effect on the evolution of the cultures, but increased insulin release. This increase was almost compensated for by the stimulation of insulin biosynthesis. After 9-10 days of culture, insulin release in response to 15 mM glucose or 10 mM leucine was studied with perifused islets. In control islets, glucose produced a sustained increase in insulin release, which, however, was 6-fold smaller than that produced by leucine. Addition of forskolin or TPA to the perifusion medium markedly amplified the response to glucose without causing a biphasic pattern of release. In islets cultured with forskolin, the insulin response to glucose or leucine was decreased, largely owing to the lower insulin stores. In islets cultured with TPA, the insulin response to glucose or leucine was also decreased, but these differences cannot be explained simply by changes in insulin content. Neither treatment affected the kinetics of release. In conclusion, acute stimulation of adenylate cyclase or protein kinase-C markedly increased insulin release from fetal islets without causing an adult-like biphasic pattern of secretion. Chronic stimulation did not accelerate maturation of B-cells.

Adenylyl Cyclases↗
PubMed1988

In vitro cytodifferentiation of perinatal rat islet cells within a tridimensional matrix of collagen.

Cell suspensions prepared by collagenase digestion of pancreases obtained from rat fetuses (21.5 d old) and newborns (2.5 d old) were mixed with a collagen solution and inoculated on a collagen base layer. At the onset of the culture, most acinar cells became necrotic, whereas other epithelial cells proliferated. Most of the cell clusters arranged themselves into simple polarized structures composed of epithelial cells forming hollow spheres, and from these budded neoformed endocrine islets. Scarce fibroblasts were located close to these structures. Immunocytochemical localization of insulin and glucagon, as well as ultrastructural characteristics of the cell types revealed an intrainsular distribution similar to the in vivo localization. Tridimensional matrix of collagen offers, to perinatal pancreatic cells in culture, an environment close to the in vivo conditions: cells reorganize themselves in tissuelike structures and cell interactions concerned in the cytodifferentiation of pancreatic islets occur. This system allows for the study of undifferentiated epithelial cells--the presumed stem cells--differentiating and differentiated endocrine cells in the same preparation.

Animals↗
PubMed1988

The aging of the endocrine pancreas of the rat. I. Parameters of cell proliferation.

Morphometrical analysis of the endocrine pancreas of senile 30-month-old rats revealed that the volume density as well as the numeric density of islets of Langerhans were much lower than in 24-month-old rats, which coincided with a much higher percentage of pycnotic nuclei in islet cells. The proportion and localization of the different categories of endocrine cells (A, B, D and PP) remained however unchanged with aging. The apparent problem of cell renewal observed in vivo in the very old age was detected earlier in vitro by tritiated thymidine incorporation. Such experiments showed that 24-month-old islet cells had a decreased labelling index when compared to 3-month-old cells. The proliferation capacity of the old cells could be partially increased by changing the serum concentration or type. Similarly as being more sensitive to serum factors, these cells underwent also more pronounced negative influence of high oxygen pressure on replication. A stereological analysis of the ultrastructure of non-degenerated B-cell nuclei revealed that with age, the relative volume of the condensed chromatin increased progressively at the expense of the dispersed form. This suggests that the still functioning senile B-cells could reduce their transcriptional activity.

Aging↗
PubMed1988

The aging of the endocrine pancreas of the rat. II. Cytoplasmic parameters of the B-cell, including insulin synthesis and secretion.

Comparative ultrastructural stereology of 6 and 24-month-old rat B-cell cytoplasm revealed an increase with age in secondary lysosomes and a decrease in the volume density of RER and Golgi apparatus. The reduction of RER observed in freshly isolated islets could affect (pro)insulin biosynthesis in vitro: if the initial mobilization of precursor molecules for protein synthesis was the same, a delay was noted in their transit to the Golgi apparatus in B-cells of old islets. No further differences were seen in the autoradiographic distribution of radioactive amino-acids. More, the stock of insulin granules was similar in all age groups in both in vivo and in vitro conditions. Neither were any differences observed in the insulin secretion into culture media as well as during a subsequent incubation in supraphysiological glucose concentrations.

Aging↗
PubMed1988

Immunocytochemical localisation of GABA in endocrine cells of the rat entero-pancreatic system.

The occurrence of GABA-containing cells in the rat entero-pancreatic system was investigated by using anti-GABA-glutaraldehyde antibodies at the light and electron microscope level. In the pancreas, the B cells showed intense immunoreactivity, contrary to non-B and exocrine cells. Moreover, post-embedding immunogold staining was localised mostly in mitochondria, close to rough endoplasmic reticulum and in the nucleus. The insulin granules appeared nonsignificantly stained, which suggests the lack of cosecretion of GABA together with insulin. In the duodenum, GABA immunoreactivity was detected in certain endocrine cell types, suggesting a possible interaction with this amino acid. The well established GABAergic innervation in the enteric system was also confirmed by immunolabelling.

Animals↗