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Biomedical subjects

B Colenbrander

Publications and source records attributed to B Colenbrander.

At least 55 records · Page 3Linked to original sources
PubMed1988

Are (13C)cortisol and (3H)cortisol metabolized identically to natural cortisol in adrenalectomized piglets?

Adrenalectomized piglets were intravenously administered a mixture of (13C4)cortisol and (3H)cortisol and natural cortisol to determine if the two tracers are metabolized identically to natural cortisol. Urine was collected after 0.5, 1.0, 1.5 and 2.0 days and the isotope dilution was measured in the four major urinary cortisol metabolites, namely tetrahydrocortisone (THE), tetrahydrocortisol (THF), alpha- and beta-cortolone in the cumulative urines. In contrast to other studies, because of the sensitivity of the method used to measure the 13C4 enrichment, non-cumulative urine collections were also analysed. Quantification of the 13C4 isotope enrichment was carried out by gas chromatography/mass spectrometry with selected ion monitoring. The specific activities of the metabolites from the cumulative urine collections were determined by high-performance liquid chromatography and scintillation counting. Small secondary isotope effects seemed to occur during the metabolism of (13C4)cortisol, as a decrease in isotope enrichment in all four metabolites was measured. These effects were easily observed with alpha- and beta-cortolone isolated from the cumulative urine collections; the enrichment decreased by 19% and 14%, respectively. The lowering in isotope dilution in THE observed in the 2.0 day cumulative urine collection in piglets 1 and 2 were 4% and 3%, respectively. A lowering in isotope dilution in THF in the 2.0 day cumulative urine collection could be observed in piglet 2, namely 7%, but no change in isotope dilution could be seen in piglet 1. These secondary isotope effects could only be observed in the 2 days cumulative urine, and not in the cumulative urines collected over shorter times. The non-cumulative urines collected at half-day periods showed a significant decrease in isotope dilution in THE and THF isolated from the urine collected after 1 day. No statistically significant isotope effects were observed with the metabolism of (3H)cortisol, except at 0.5 day when the specific activity in the cortolones was lower and that in THF was higher. However, at 0.5 day with THE and 1.0 day with THF and the cortolones the specific activities remained approximately 6% higher than that administered in the cortisol. Secondary isotope effects with tritiated cortisol may have occurred but because of the relatively large imprecision of the measurement (SD = 3-4% with THE and THF and the cortolones (SD approximately 8%) compared to the measurements of the 13C4 enrichment (SD approximately 2%) these effects could not statistically be proven.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenalectomy↗
PubMed1988

Prolactin in the developing pig.

Prolactin (PRL) was determined in plasma of fetal pigs from 40 days post coitum (d.p.c.) onwards. Values increased in the last 3 wk of the gestational period and reached 10 ng/ml at term. Immunoreactive lactotropes could be identified as early as 31 d.p.c. Lactotrope development appeared to be biphasic, with no apparent increase in cell number in the 51-75 d.p.c. period. Sex differences in volume percentage of lactotropes and plasma PRL levels were observed in the 71-75 d.p.c. period. Pituitary PRL content increased 20-fold between 95 d.p.c. and term and 10-fold between birth and 6 wk. Volume percentage of lactotropes did not change from birth to 6 wk. In the postnatal period, plasma PRL concentrations were high in the first 1-2 wk and they decreased thereafter. Lower stable values were observed until about 10 wk, when PRL concentrations began to increase. Prepubertal peak levels were observed in the 10- to 16-wk period and a pubertal peak was observed at 20-22 wk. No significant differences between plasma PRL profiles of males and females were observed in the postnatal period. Castrated males, however, had consistently lower plasma PRL concentrations than intact boars. Cryptorchid boars had PRL concentrations comparable to intact boars. The PRL profile, in relation to the pattern of gonadal development, suggests a role for PRL in gonadal development of the pig.

Animals↗
PubMed1987

Feedback regulation of gonadotropic hormone secretion in neonatal pigs.

The effect of castration and of administration of charcoal-treated porcine follicular fluid (pFF) containing inhibin-like activity on plasma concentration of gonadotropic hormones was studied in neonatal pigs. Plasma follicle-stimulating hormone (FSH) concentration averaged 25.1 +/- 1.5 ng/ml (mean +/- SEM) in 1-wk-old females and gradually declined to 20.2 +/- 0.7 ng/ml 6 wk later. Ovariectomy did not significantly influence plasma FSH concentration. In males, concentration averaged 8.0 +/- 0.7 ng/ml before castration but rose significantly within 2 days after castration. Injection of luteinizing hormone-releasing hormone (LHRH) did not influence plasma FSH concentrations in intact males, but did in females and in 7-wk-old males castrated at 1 wk. Plasma luteinizing hormone (LH) concentrations in 1-wk-old females (2.2 +/- 0.4 ng/ml) gradually declined and were not influenced by castration. Concentrations of plasma LH in 1-wk-old male piglets (2.8 +/- 0.7 ng/ml) were not significantly influenced by castration within 2 days but were significantly higher 6 wk later. LHRH induced a significant rise in plasma LH concentrations in all animals. Injection of pFF resulted in a decline of plasma FSH concentrations in intact and castrated males and in intact females, but did not influence plasma LH concentrations. These data demonstrate a sex-specific difference in the control of plasma FSH, but not in plasma LH concentration in the neonatal pig. Plasma FSH concentrations, but not plasma LH concentrations, are suppressed by testicular hormones in 1-wk-old piglets. Plasma FSH concentrations can be suppressed in both neonatal male and female pigs by injections of pFF.

Aging↗
PubMed1987

The ultrastructure of normal fetal and neonatal pig testis germ cells and the influence of fetal decapitation on the germ cell development.

The development of germ cells in the male pig was investigated ultrastructurally in normal and decapitated fetuses. The age ranged respectively from 30 days p.c. till one month after birth and from 52 days p.c. until birth. The ultrastructural organization of the germ cells changes dramatically between 30 days p.c. and 52 days p.c. which coincides with the formation of 'true' sex cords. From 52 days p.c. onwards the morphology is rather stable: cells show a 'hydrated' appearance and typical cell bridges. There is no obvious difference in the ultrastructure of germ cells in decapitated animals, their normal littermates and control animals. Therefore germ cell development in the pig is likely to be insensitive to gonadotropins during the fetal period. The development of pig germ cells follows closely the pattern described for several species. Quantitatively there is an increase in the ratio of germ cell/Sertoli cell per cross sectional diameter in the decapitated animals.

Animals↗
PubMed1986

Changing basal and stimulated activity of the renin-angiotensin system during the second half of gestation in the anaesthetized piglet.

Concentrations of components of the renin-angiotensin system were studied in eighty anaesthetized pig fetuses aged between 57 and 112 d of gestation (term = 114 +/- 1 d). Plasma renin concentration rose from a mean value of 3.2 +/- 0.4 ng X ml-1 X h-1 (mean +/- S.E.M.) at 57 d to 17.5 +/- 2.7 ng X ml-1 X h-1 at 93 d of gestation and thereafter declined to 5.0 +/- 1.6 ng X ml-1 X h-1 just prior to term. There was no distinct pattern of change in plasma renin substrate concentrations during gestation; the concentration near term (0.33 +/- 0.10 micrograms X ml-1) was not different from that at 57 d (0.50 +/- 0.18 micrograms X ml-1) or that at 93 d (0.31 +/- 0.08 micrograms X ml-1) of gestation. Plasma angiotensin II concentrations increased from 33 (log10 (mean +/- S.E.M.) = 1.554 +/- 0.050) pg X ml-1 at 60 d to 232 (2.365 +/- 0.225) pg X ml-1 at 105 d of gestation, after which it decreased to 50 (1.699 +/- 0.100) pg X ml-1 in 20-d-old neonatal piglets. Haemorrhage of 10-20% estimated blood volume produced no consistent changes in plasma renin substrate concentrations, and inconsistent changes in renin and angiotensin II concentrations at 85-90 d of gestation, but a consistent increase in both renin and angiotensin II concentrations thereafter. These results indicate that the components of the renin-angiotensin system are present in the circulation of the pig fetus, and that their responses to stimuli develop during the second half of gestation.

Anesthesia↗
PubMed1986

Ontogeny of hypothalamic pituitary function in the pig: pituitary thyrotrophin in the fetus and neonate.

Thyrotrophin in individual pituitaries obtained from fetal and prepubertal pigs was quantified by homologous radioimmunoassay (RIA) and heterologous radioreceptor assay (RRA). Relative evolution of pituitary TSH contents and concentrations with age were in good agreement as measured by both assay systems although the quantity of TSH detected by RRA appeared consistently lower than that measured by RIA. Thyrotrophin was first detected in pituitaries of fetal pigs at day 75 of gestation. Thereafter the pituitary content of TSH increased to approximately 45 micrograms/pituitary in the oldest group tested (6 weeks of age). The pituitary TSH concentration rose sharply until birth (114 +/- 1 day post coitum) and thereafter remained increased at a concentration of approximately 400 ng/mg wet weight.

Animals↗
PubMed1986

Kinetic measurement of the urinary production rate of cortisol in male piglets: is the prerequisite 'collection until all label has disappeared' necessary?

Urinary cortisol production rate (CPR) was calculated by two different methods in five male piglets (about 3 kg bodyweight) injected i.v. with 40-120 kBq tritiated cortisol ([3H]F. After administration of [3H]F, urine was obtained from four consecutive collections for the following 2 days, during which 80-100% of the label was recovered. Total radioactivity in the urine was measured and used to calculate the total rate constant of 0.115 +/- 0.011 h-1 and, from this, the mean biological half-life (t1/2) of 6.0 +/- 0.6 h (S.D.; n = 4). It was found that the mass ratio of the two principal urinary cortisol metabolites tetrahydrocortisone (THE) and tetrahydrocortisol (THF) was strikingly less than 1.0 (0.4 +/- 0.1; n = 14), which is the reverse of that observed in older pigs, neonatal infants and man. To calculate CPR conventionally, the cumulative specific activities of THE and THF were calculated for the 2-day period of urine collection. The apparent mean CPR values on the basis of THE and THF were calculated as 11.5 +/- 1.6 (n = 5) and 12.8 +/- 3.3 (n = 5) mumol/day respectively, and 12.1 +/- 1.4 (n = 5) mumol/day for the average of THE and THF. The second method for calculating CPR consisted of determining the masses of THE and THF (mumol) per fraction of dose (m/fd) (fd refers to the ratio of radioactivity in the metabolite and dose) at different times after administration of [3H]F. The calculated m/fd values, which are synonymous with the dose divided by the specific activities of the metabolites, and the different times of urine collection were analysed by linear regression. The resulting slope is equal to the CPR. The CPR derived by this method for the average of THE and THF, 10.1 +/- 0.91 mumol/day was significantly (P less than 0.014) lower than that derived conventionally, 12.1 +/- 1.40 mumol/day. This second method may be used when CPR is determined in neonatal infants by means of nonradioactive, deuterated or 13C-enriched cortisol, where the extent of negative feedback by the relatively high dose of exogenous steroid on cortisol secretion must be kept as low as possible. This method also allows urine collections to be used at times when the tracer is still being excreted.

Animals↗
PubMed1986

Some histochemical and ultrastructural observations on the early foetal pig testis.

Testes of foetal pigs between 26 to 35 days post coitum (p.c.) were investigated histochemically and ultrastructurally. Diaphorase and delta 5-3 beta-hydroxysteroid dehydrogenase activities were studied using, respectively, NADH and pregnenolone and dihydroxy androsterone as substrates. Ultrastructurally, attention was focused on the development of mesenchymal cells and on the sustentacular cells in the primitive sex cords in an attempt to detect the origin of Leydig cells. Histochemically there is a concentration of activity toward the interstitium with increasing age. Also the reactions increase in intensity. Ultrastructurally no evidence for Leydig cell development from Sertoli cells could be observed. Mesenchymal cells between the sex cords show a development toward Leydig cells. This is absent in mesenchymal cells in the future tunica albuginea. Before 30 days p.c. no 'true' Leydig cells can be observed morphologically. The role of the rough endoplasmic reticulum/mitochondrial complex, which is present in many mesenchymal and sustentacular cells, is discussed.

3-Hydroxysteroid Dehydrogenases↗
PubMed1985

The ontogeny of hypothalamic pituitary function in the pig. I. Pituitary LH and FSH in the fetus and neonate.

Pituitaries were collected from fetal and postnatal pigs from day 55 p.c. until 6 weeks after birth at closely spaced intervals. LH and FSH in individual pituitaries were quantified by both homologous RIA and homologous RRA. No significant difference was found between results obtained by RIA and RRA. Both LH and FSH are first detected by RIA and RRA in the porcine fetal pituitary at 75 days p.c. Thereafter both LH and FSH pituitary content rises until term. LH pituitary concentration in both male and female fetuses and FSH pituitary concentration in males exhibit a peak just before birth. FSH pituitary concentration in females rises until birth and thereafter remains elevated. A statistically significant sex difference was found postnatally with regard to FSH content and concentration but not for LH.

Animals↗
PubMed1985

Development of pituitary gonadotropic cells in the pig fetus and the effect of luteinizing hormone-releasing hormone administration.

Pituitary gonadotropic development in fetal pigs has been studied immunocytochemically. From 50 days postcoitum (p.c.) until 90 days p.c. the volume density of luteinizing hormone (LH) immunoreactive cells increased from 0.12% to 0.61% of the glandular mass of the anterior part of the pituitary gland. From 90 to 100 days p.c. a steep increase to 4.5% was found. A single injection of long-acting luteinizing hormone-releasing hormone (LHRH) to the fetus at 75 days p.c. inhibited this developmental pattern. Pulsatile administration of LHRH agonist to fetuses from 70 to 73 days p.c. had no significant effect on the volume density of LH immunoreactive cells, whereas pulsatile administration from 70 to 80 days p.c. and from 95 to 105 days p.c. inhibited the normal increase of this parameter. It is concluded that from 70 days p.c. onwards the development of fetal gonadotropic cells can be manipulated by exogenous LHRH.

Animals↗
PubMed1985

Effect of somatostatin and thyrotrophin-releasing hormone on the levels of growth hormone in the circulation of the chronically catheterized pig fetus in utero.

The effects of i.v. administration of thyrotrophin-releasing hormone (TRH) and of somatostatin on circulating plasma levels of porcine GH in the chronically catheterized pig fetus have been examined. Growth hormone levels increased markedly (P less than 0.01) following TRH administration, but there was no change in thyroxine levels by 1 h after treatment. Administration of somatostatin caused a significant (P less than 0.05) decrease in mean GH levels, but the response was variable between pigs. Saline administration had no significant effect on GH levels. These results suggest that the mechanisms regulating postnatal GH release are present in the fetal pig, but may not be fully developed 8-12 days before delivery.

Animals↗
PubMed1984

Leydig cell development in the pig testis during the late fetal and early postnatal period: an electron microscopic study with attention to the influence of fetal decapitation.

The ultrastructure of fetal and postnatal pig Leydig cells was studied from 75 days postcoitum (p.c.) to 1 month after birth. Additionally, decapitated fetuses from 75 days p.c. until birth were used to study the effect of deprivation of gonadotrophins on the ultrastructure of Leydig cells. Normal Leydig cell development was characterized by a change in smooth endoplasmic reticulum (SER). Next to branched tubular SER, whirls of elaborate and tightly packed SER membranes appeared. The amount of SER increased with age but decreased slightly before the end of the observation period. Rough endoplasmic reticulum (RER) was a minor component. Large bundles or whirls of intermediate filaments were abundant until just before birth; thereafter, they decreased drastically. Peroxisome-like structures and crystalloid bodies were observed with increasing frequency from 75 days p.c. and 20 days postpartum onward. Polygonal lysosome-like dense bodies transformed into complex membranous structures especially after birth. Giant mitochondria occurred in the late fetal and postnatal period. From 75 days p.c. onward fully developed Leydig cells were scarce in testes of decapitated fetuses. Leydig cell characteristics disappeared toward the end of the fetal period; only the cell shape, the large bundles or whirls of intermediate filaments, some scarce polygonal lysosome-like dense bodies, and RER remained, but SER was negligible. Progressive hemorrhages apparent in situ were correlated positively with fetal age. The dependency of Leydig cells upon LH began between 60 and 75 days postcoitum.

Animals↗
PubMed1984

Sertoli cell development of pig testis in the fetal and neonatal period.

The Sertoli cells of pig fetuses from 35 days postcoitum until 1 mo after birth have been investigated by light and electron microscopy in decapitated animals and their control littermates, as well as in untreated animals. Until 52 days postcoitum, Sertoli cells change in form during the formation of sex cords but from then onwards they are rather uniform. They primarily display an elongated nonindented nucleus with one or more prominent nucleoli, a well-developed Golgi apparatus, and in the basal compartment below or beside the nucleus, a large lipid droplet. There are large quantities of rough endoplasmic reticulum (RER) from 52 days postcoitum onwards, often with complex whirl forms and a parallel arrangement of profiles with relatively few ribosomes. After birth their numbers seem to be somewhat less, and by 1 mo after birth the RER profiles are often shorter and almost free of ribosomes. Clustered ribosomes are found in large quantities throughout the period under investigation. Especially in the early fetal period, the endoplasmic reticulum (ER) profiles show prominently filled cisternae. Mitochondria are mostly long and slender, or small and ovoid. Most have lamellar cristae, but mixed lamellar-tubular cristae can also be seen. Between decapitated, control and untreated animals no obvious ultrastructural differences could be observed. The peritubular cell sheath surrounding the sex cords did not show signs of differentiation into a layer of myoid cells.

Animals↗
PubMed1984

Perinatal development of tubular function in the pig.

Renal tubular function has been studied in pig fetuses of 105-112 d gestational age in new-born pigs 5-9 d old. The experiments were performed on anaesthetized animals, urines being collected by inserting a catheter into one ureter of the animal under study. The glomerular filtration rate was estimated and plasma concentrations and urinary excretion of the following substances were measured: sodium, potassium, calcium, ammonia, urea, phosphate, glucose fructose, creatinine, protein and exogenous 4-aminohippuric acid, and inulin. The reabsorption of water was considered in relation to the plasma vasopressin values. New-born pigs were loaded with glucose and fructose in order to determine the maximal tubular transport rate of these substances. Significant changes at birth occur in only a few functions of the tubulus system. Following delivery, major changes are: (1) the increased reabsorption of sodium and water which is probably the most important adaptation to extra-uterine life; (2) an apparent increasing impermeability of the tubular epithelium for creatinine, and (3) the direction of transport of fructose, which is reabsorbed by fetuses whereas neonates demonstrate a net secretion. Glucose and fructose are transported by different mechanisms. The experiments with fructose-loaded piglets demonstrate that there are at least two transport mechanisms for fructose: reabsorption - either passive or active - and secretion. The factors causing a shifting from one mechanism to the other are not yet known.

Absorption↗
PubMed1984

Effects of adrenergic agonists and antagonists on the blood pressure and heart rate of the pig fetus.

The effects of adrenergic agonists and antagonists on blood pressure and heart rate were investigated in 18 chronically catheterised pig fetuses aged between 102 and 109 days of gestation (term is 114 days). One fetus had been decapitated in utero at 42 days of gestation. The alpha adrenergic agonist methoxamine produced a small but dose dependent hypertension and a dose related slowing in heart rate. The beta adrenergic agonist isoprenaline decreased mean arterial pressure in a dose related manner and produced tachycardia. Propranolol, a beta adrenergic blocker, increased mean arterial pressure and decreased heart rate. The response to subsequent alpha adrenergic blockade with phentolamine was hypotension and a slight bradycardia. Decapitation at 42 days of gestation did not seem to change the fetal responsiveness to adrenergic agonists but removed the blood pressure response to beta blockade. These observations indicate that the heart and circulation of the pig fetus are under adrenergic vasomotor control during late gestation.

Adrenergic Agonists↗
PubMed1984

Cytoplasmic filaments in fetal and neonatal pig testis.

Leydig cells in developing fetal pig testis contained during the fetal regressive phase large accumulations of intermediate filaments. Before and after this period these filaments were arranged in a criss-cross fashion. In the pig as well as in the dog testis these filaments have been characterized as vimentin. Within the vimentin aggregates occasionally a weak positive actin reaction was seen in pig but not in dog Leydig cells. Microfilaments were hardly observed. Most Sertoli cells contained a layer of actin microfilaments close to the basal cell membrane. In the lower cell compartment and around the nucleus (intermediate) vimentin filaments could be observed in a criss-cross configuration.

Aging↗
PubMed1983

Development of nervous tissue in the heart of the fetal and neonatal pig and the effect of decapitation in utero.

The development and distribution of the nerves in the heart of the pig was studied macroscopically and by light microscopy. Hearts were collected from 86 fetuses between 31 and 114 days of gestation (term = 114 days), from 12 neonatal pigs aged 9 and 20 days and from 6 adult sows of the Dutch Landrace breed. The effect of vagotomy produced by decapitation in utero at 40-43 days was studied in an additional 24 hearts from fetuses aged between 51 and 114 days of gestation. The amount of acetyl-thiocholine reactive fibres increases in the atria, A-V node and ventricles throughout gestation. At every age the amount of nervous tissue is highest in the A-V node and lowest in the ventricles. Hearts from decapitated fetuses have smaller amounts of nerve tissue than those from intact fetuses at every age studied. Ganglia are present in both intact and decapitated fetuses. Fluorescent cells containing catecholamines are observed in hearts from fetuses as young as 35 days gestation. Although fluorescent nerve fibres are rarely seen in hearts at 70 days gestation, more fibres are present near birth and thereafter there appears to be a considerable increase in the number of fibres and in the intensity with which they fluoresce. These results show that there is substantial nerve growth into the heart of the pig during gestation and that catecholamine containing nerve fibres develop later than those reactive to acetyl-thiocholine.

Animals↗