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B Barenton

Publications and source records attributed to B Barenton.

At least 37 records · Page 2Linked to original sources
PubMed1988

In vitro regulation of growth hormone (GH) release from ovine pituitary cells during fetal and neonatal development: effects of GH-releasing factor, somatostatin, and insulin-like growth factor I.

Using a monolayer approach, we have examined the acute (3 h) effects of GRF, somatostatin (SRIF), and insulin-like growth factor I (IGF-I) on GH release from pituitary cells of male and female 70-, 100-, and 130-day-old fetuses and newborn lambs and of prepubertal male lambs. GRF stimulated basal GH release in a dose-dependent (10(-12)-10(-8) M) manner at each stage in development. There was no linear relationship between maximal response and increasing age of the donor animals. The ED50 values for GRF were similar in all groups, except in the pituitaries from male and female 130-day-old fetuses, where the ED50 values were significantly higher. SRIF elicited a dose-related (10(-10)-10(-6) M) inhibition of basal GH secretion at each stage of fetal life and in the prepubertal period; although the response was lower in the youngest fetal pituitaries, there was no significant change in maximal response during the fetal or prepubertal period. No effect of SRIF on basal GH secretion was observed in newborn lambs. However, SRIF (10(-7) M) was able to block GRF (10(-8) M)-stimulated GH release in 100- and 130-day-old fetal and prepubertal as well as newborn lamb pituitary cells. Plasma IGF-I concentrations increased from 15.0 +/- 0.7 (mean +/- SE) and 13.8 +/- 0.9 ng/ml for male and female animals, respectively, at 70 days gestation to 55.8 +/- 3.2 and 51.8 +/- 11.1 ng/ml at the time of birth. The increase was much more pronounced in prepubertal lambs, especially in male animals, where IGF-I levels reached 300.8 +/- 37.7 ng/ml. IGF-I (100 ng/ml) had no effect on basal GH release in 70- and 100-day-old fetal, newborn, and prepubertal lamb pituitary cultures, but significantly inhibited basal GH secretion from 130-day-old fetal cells. This dose of IGF-I had no effect on GRF (10(-9) M)-stimulated GH release at 70 days gestation. It significantly inhibited this effect at 100 days and in prepubertal lamb cells. In 130-day-old fetal and newborn lamb pituitary cultures, IGF-I completely blocked the GH response to GRF.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1988

Insulin-like growth factor-binding proteins in hypophysectomized rat liver: characterization and subcellular localization.

We have characterized binding proteins for insulin-like growth factors (IGFs) in hepatic subcellular fractions and in the washed supernatants of these fractions in normal and hypophysectomized (hypox) rats. In the course of assessing IGF-II-binding sites on rat liver microsomes, we observed that [125I] IGF-II binding to the microsomal membranes of hypox rats was much lower than that in normal rats. Paradoxically, binding increased in hypox animals at low concentrations (0.5-5 ng/ml) of unlabeled IGF-II. After resuspension and centrifugation (washing) of the microsomes, no difference was found in [125I]IGF-II binding to hypox vs. normal microsomes. However, the binding of [125I]IGF-II to the washing supernatant (SN) from hypox rat microsomes was greater than binding to that from normal animals. Binding to SN was inhibited by unlabeled IGF-II in a dose-dependent manner. Scatchard analyses indicated that the affinity constant for binding by hypox SN was higher than that of normal SN and the microsomal fractions of both hypox and normal rats. After further subfractionation of the liver, no binding activity was found in SN from plasmalemma, whereas it was about 20% of input counts per min of [125I]IGF-II in SN from combined Golgi-endosome fractions of hypox rat liver. We next compared IGF-binding moieties in microsomal SN with those in plasma using cross-linking of [125I]IGF-II followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In normal rat plasma, we observed the presence of 42K, 39K, 31K, and 27K binding complexes. In hypox rat plasma only a 42-39K doublet was found. In the SN of normal rat microsomes, the predominant complex migrated at 39K and was distinguishable only after acidification. In the SN of hypox rat microsomes, the 42K complex was predominant, with a minor 34K complex. These studies have identified IGF-binding moieties in hepatic tissues, particularly in hepatic vesicular elements, which interfere in the binding of IGF-II to membrane receptors. Their presence in these receptor-rich elements may influence IGF binding to intracellular receptors and, hence, the biological activity of the peptide.

Animals↗
PubMed1988

[Effects of GRF 1-29 in normal and hypotrophic lambs].

Injections of hGRF rapidly stimulated GH secretion in lamb and this response was significantly higher in hypotrophic than in normal lambs. The treatment had an effect on body composition reducing the retention of lipids and the energy level and increasing calcium and phosphorus content. The results showed that GRF affected both metabolism and skeletal growth of ruminants, stimulating specially the production of Sm-C and proliferation of chondrocytes.

Animals↗
PubMed1987

Specificity of insulin-like growth factor binding to type-II IGF receptors in rabbit mammary gland and hypophysectomized rat liver.

We have reevaluated IGF binding specificity to membrane receptors in rabbit mammary gland (RMG) and hypophysectomized rat liver (HRL) using recombinant DNA-derived and synthetic analogues of human IGF-I and highly purified IGF-II. SDS-PAGE demonstrated that [125I]IGF-I bound to type-I IGF receptors in RMG; this binding was inhibited in a similar fashion by the IGF-I analogues (IC50 = 10 ng/ml) and to a lesser extent by IGF-II (IC50 = 60 ng/ml). [125I]IGF-II bound to type-II IGF receptors in both RMG and HRL. The IC50 for IGF-II was 9 and 3 ng/ml with RMG and HRL, respectively. At a dose as high as 1 microgram/ml, IGF-I analogues inhibited less than 20% of [125I]IGF-II binding. These results suggest that IGF-I has little or no affinity for type-II IGF receptors.

Animals↗
PubMed1987

Effects of hypothalamic hormones (GRF, TRH, somatostatin) and insulin-like growth factor I on growth hormone secretion from prepubertal male lamb pituitary cultures.

We have examined the regulation of GH secretion from monolayer cultures of prepubertal male lamb anterior pituitary cells. Growth hormone-releasing factor (GRF 1-44) stimulated GH release in a dose-related manner: the maximal effective dose was 10(-10) M, which caused a 500% increase in basal GH secretion, while the half-maximal effect was reached with a dose of 2.5 x 10(-11) M (ED50). Thyrotropin-releasing hormone (TRH) also elicited a dose-dependent stimulation of GH secretion, although it was approximately 1000 times less potent than GRF. GRF and TRH did not have additive or synergistic effects on GH secretion. Somatostatin (SRIF) at a concentration of 10(-7) M maximally inhibited basal GH release to 40% of that of the control; the ED50 was 2.0 x 10(-9) M. Moreover, 10(-7) M SRIF blocked the stimulation of GH secretion induced by 10(-8) M GRF. However, when the cells were incubated with these two peptides at an identical concentration (10(-8) M), GH secretion was stimulated significantly above control values. When added at the same concentration (10(-7) M, TRH ans SRIF nullified their respective effects. A dose of 100 ng/ml of synthetic IGF-I was without effect on basal GH release, but significantly decreased 10(-9) M GRF-induced stimulation of GH secretion. these data indicate that in prepubertal male lambs: the stimulatory effect of GRF is predominant over the inhibitory effect of SRIF, somatostatin inhibits TRH stimulation of GH secretion in vitro, and IGF-I may control GH secretion by modulating GRF effects at the pituitary level.

Animals↗
PubMed1987

Characteristics of growth hormone response to the administration of growth hormone-releasing hormone (GRF) in the lamb.

Human growth hormone releasing hormone (GRF 1-44 or GRF 1-29) was administered to lambs at two different physiological stages (suckling: 5-6 week-old and weaned: 14-15 week-old) when growth hormone (GH) secretory patterns were different: suckling lambs exhibited flat basal GH profiles (5-10 ng/ml) while the weaned lambs had frequent spontaneous episodes of GH release (15-65 ng/ml). The iv injection of GRF evoked an immediate release of GH. In each case, plasma GH levels reached a maximum 1-4 min after the injection. The secretory spike was multiphasic and lasted 30-60 min. Administration of GRF (0.1 microgram/kg) in weaned lambs induced GH pulses with an amplitude comparable to that of endogenous peaks. The induction of a GH peak occurred even when a spontaneous peak immediately preceded the GRF injection. Also, spontaneous peaks were observed during the hour following a GRF-induced GH peak. In suckling lambs, GRF injected intravenously as a single bolus in a range of 0.01 to 0.5 microgram/kg (2 to 100 pmoles/kg) stimulated GH release in a dose-dependent manner. Chronic administration of GRF (0.75 nmole GRF 1-44 or GRF 1-29 per kg twice daily for 21 days) in newborn lambs increased significantly (p less than 0.001) the acute response to GRF during the course of the treatment. GH response to GRF 1-44 and GRF 1-29 was the same. These data show that lambs are highly responsive to GRF action during both suckling and weaning and suggest that there is no in vivo desensitization of the pituitary gland after acute or chronic GRF administration.

Animals↗
PubMed1987

Effects of TRH and GRF administration on GH, TSH, T4 and T3 secretion in the lamb.

The effects of various amounts of thyrotropin-releasing hormone (TRH) injected subcutaneously or intravenously (alone or in combination with growth hormone-releasing factor: GRF 1-44) on growth hormone (GH), thyroid-stimulating hormone (TSH), thyroxine (T4) and triiodothyronine (T3) were studied in the plasma of 2-week, 2-month and 3-month old lambs. After subcutaneous TRH administration, increases in plasma TSH, T4 and T3 levels were equivalent, whatever the amount of TRH used (1,2,5 or 10 micrograms/kg). These responses lasted longer after 5 and 10 micrograms/kg. After intravenous TRH administration in 2-week old lambs, the maximal increase in plasma TSH levels occurred after the injection of 0.25 microgram/kg. However, plasma T4 and T3 responses were not different, whatever the amount used. As previously, the amount of TRH affected the duration of these responses more than the magnitude of the pituitary-thyroid axis response. Whatever the injection route, amount used or animal age, TRH alone did not increase GH secretion in lambs. However, it slightly delayed the GH response to GRF. GRF did not affect the response of TSH and T4 to TRH; however it could inhibit T3 increase. In conclusion, in contrast to results obtained in calves by Hodate et al. (1985), TRH did not enhance GH secretion in lambs but, as expected, induced sharp increases in plasma thyroid hormone levels. Its classification as a "growth factor" is therefore questionable, at least in lambs.

Animals↗
PubMed1987

Secretory profiles and production rate of growth hormone in ruminant lambs.

Secretory profiles and production rates of growth hormone (GH) were determined in 6 ruminant lambs during winter. The mean GH concentrations (3.78 +/- 2.17 ng/ml) calculated were based upon blood sampling obtained every 3 min using a withdrawal pump. Body clearance (0.162 +/- 0.031 1/h/kg) was calculated from bolus intravenous oGH administration. The data were analysed by non-linear regression analysis; a bicompartmental model was selected to describe the data. production rate was 14.6 +/- 7.98 micrograms/kg/24 h. It has been emphasized that the experimental design used gave an accurate estimate of GH production rate.

Animals↗
PubMed1987

Insulin-like growth factor (IGF) binding in hypophysectomized rat liver microsomes: alteration by a soluble binding moiety.

In this study, we compared the binding of IGF-I and IGF-II to liver microsomes of normal and hypophysectomized (Hypox) rats. The binding of [125I]-IGF-II, measured by centrifugation of membrane-bound ligand, was lower in hypox than in normal rats (15 +/- 2 vs 26 +/- 1%, p less than 0.001) but binding was increased (46 +/- 1.5 vs 31 +/- 1%, p less than 0.001) when bound and free hormones were separated using polyethyleneglycol (PEG) precipitation. This was due to the presence of soluble binding activity which dissociated from membranes to compete for IGF binding. When soluble binding activity was first removed from microsomal membranes by a washing procedure no difference was found in [125I]-IGF-II binding to microsomes of Hypox and normal animals (33 +/- 1 s 32 +/- 1%). However, in the microsomal washing supernatant from Hypox (containing soluble binding activity) IGF-II binding was much higher than in that from normals (17 +/- 2 vs 6 +/- 0.5%, p less than 0.001). The binding of [125I]-IGF-I was lower than that of [125I]-IGF-II but was comparably changed. By contrast, [125I]-insulin binding was similar in Hypox and normal rats and was not influenced by PEG precipitation or prewashing of the membranes. Inhibition dose-response curves showed a paradoxical increase in [125I]-IGF-II binding to unwashed microsomes of Hypox rats in the range of 0.5-5 ng/ml cold IGF-II. In normal animals [125I]-IGF-II binding to microscomes was progressively inhibited by IGF-II in a range of 0.5-500 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Influence of photoperiod and protein diet on growth hormone secretion in rams.

Studies of sheep were undertaken to determine the effects of photoperiod and protein diet on growth hormone (GH) secretion. Rams were subjected to either a control (RI) or an inverted (R2) 6-month (semestral) light regime. In both light regimes day lengths varied gradually between 8 and 16 hr. Within each light regime group of animals, the rams received either a low (L) or a high (H) protein diet containing the same level of energy. Plasma GH profiles consisting of 13 hourly samples were determined at regular intervals corresponding to known day lengths. Analysis of variance indicated that there was a significant effect of day length (P less than 0.01) and protein diet (P less than 0.05) on GH secretion, the two light regimes R1 and R2 were equivalent with respect to GH secretion, and there were no interactions among the three experimental factors. Although mean GH secretion was consistently higher in L groups than in H groups, there was a similar trend in all the animals of increasing GH secretion as day length increased. GH secretion was maximum when the day length reached 13 hr 20 min in increasing photoperiods in L groups (15.6 +/- 1.6 ng X h X ml-1) and 16 hr in H groups (13.0 +/- 1.2 ng X h X ml-1). From these results we conclude that both an increasing day length and a deficiency in protein diet stimulate GH secretion in rams but the GH response to these two factors may involve different regulatory processes and may have different functions.

Animals↗
PubMed1986

Characterization of insulin binding to slices of slow and fast twitch skeletal muscles in the rabbit.

Insulin binding was studied in rabbit semimembranosus proprius and psoas major muscles composed of slow-twitch oxidative (SO) and fast-twitch glycolytic (FG) fibers, respectively. For this purpose, we developed a technique using cryostat microtome muscle slices. Degradation of 125(I)-insulin during the incubation period was prevented by the addition of 1 mM bacitracin in the buffer. Specific binding to muscle slices plateaued by the 24 hrs. of incubation at 4 degrees C. It increased as a function of the amount of muscle, with a maximum binding occurring at about 5 mg of muscle slices. Triton X-100 has been shown to increase specific binding from a critical concentration of 10(-4) M with a maximum effect occurring at 3.3 10(-4) M. Under this condition, the binding was specific since displacement studies showed no inhibition of 125(I)-insulin binding by GH, HCG, ACTH and glucagon, whereas half maximal inhibition was achieved using 5 10(-10) M insulin, 3 10(-9) M IGF1 and 2 10(-8) M proinsulin. The analysis of the binding data yielded curvilinear Scatchard plots. The number of high affinity insulin receptors was higher in the SO muscle than in the FG muscle (4.3 +/- 0.7 vs 0.7 +/- 0.2 fmol/mg fresh muscle; P less than 0.001) with similar high affinity dissociation constants (Kd = 1.5 10(-10) M). Analogous results were obtained using muscle microsomal fractions. The differences in insulin binding might be related to the more intense metabolism of SO fibres which contract more often than FG fibres in vivo.

Animals↗
PubMed1984

Reevaluation of lipolytic activity of growth hormone in rabbit adipocytes.

The lipolytic activities of porcine pituitary fractions and purified growth hormone (GH) from human (h), porcine (p), ovine (o) and rabbit (Rb) origin as well as ovine placental lactogen (oPL), were compared to that of ACTH on rabbit adipocytes. All the GH preparations and oPL were equivalent in inhibiting the binding of labelled oGH to liver plasma membranes from pregnant rabbits. ACTH, and to a lesser extent porcine pituitary fractions and hGH, stimulated free fatty acid production by isolated adipocytes. The sensitivity of the adipocytes to these factors was increased when adenosine deaminase was added to the incubation medium. But, RbGH, pGH, oGH and oPL had no effect. We conclude that GH is not directly involved in the control of lipolysis in rabbit adipocytes and that the effect of hGH is rather due to a contamination of this preparation by other pituitary factors.

Adipose Tissue↗
PubMed1984

Effect of prenatal treatment with busulfan on the hypothalamo-pituitary axis, genital tract and testicular histology of prepubertal male rats.

Female Wistar rats were treated with busulfan or with solvent on Day 20 of pregnancy. Thirty male offspring of each group were killed at 38 days of age. In busulfan-treated rats, compared to controls, hypothalamic LH-RH content was decreased by 52%, whereas pituitary LH and FSH concentrations were increased by 60 and 43% respectively. Plasma LH and FSH were increased by 112 and 275% respectively. Prolactin concentrations were not changed, but plasma testosterone concentration was decreased by 48%. The total number of Leydig cells per testis was decreased by 52%, and LH binding sites per testis were decreased by 70%. The total number of Sertoli cells was decreased by 44%, while FSH binding sites per testis were decreased by 62%. Spermatogenesis was practically absent after prenatal exposure to busulfan. These data demonstrate that on Day 20 of pregnancy all the dividing cells in the fetal testes were depleted by an antimitotic treatment. The stimulation of the hypothalamo-pituitary axis could have been partly induced by the decrease in testosterone production, and by the aplasia of germ cells involving modifications of the remaining Sertoli and Leydig cells.

Animals↗
PubMed1983

Endocrinological and histological changes induced by flutamide treatment on the hypothalamo-hypophyseal testicular axis of the adult male rat and their incidences on fertility.

Adult male Wistar rats were treated with flutamide from 90 to 105 days of age. In a first experiment, testis and accessory sex organs were weighed. In the same animals, hypothalamic LRH content, pituitary gonadotrophin concentrations, plasma LH, FSH, prolactin and testosterone levels, and testicular gonadotrophin receptors were evaluated. In a second experiment, fertility was tested at the end of the treatment, and histology of the testis was performed. All the results were compared to those obtained in control animals of the same age. Accessory glands of genital tract were significantly lower in flutamide-treated animals (P less than 0.01). Hypothalamic LRH, pituitary and plasma FSH, and prolactin concentrations were unchanged, while pituitary and plasma LH level and especially plasma testosterone concentration were increased (P less than 0.001). Flutamide therefore exerted a strong inhibition on testosterone-dependent organs, and blocked the negative feedback of testosterone on the hypothalamo-pituitary axis, increasing the LH levels. Testis weight, intertubular tissue volume, total number and total volume of Leydig cells/testis, as well as total length and diameter of seminiferous tubules were unchanged in flutamide treated rats. However number of LH receptors/Leydig cell, nuclear area of Sertoli cells, number of FSH receptors/Sertoli cell, number of leptotene spermatocytes and of round spermatids per cross section, and yield of spermatogonial divisions were decreased after treatment. Flutamide treatment also decreased fertility by 48% (P less than 0.05). This lowered fertility is likely the result of impaired spermatogenesis and/or a dysfunction of accessory sex organs.

Anilides↗
PubMed1983

[Demonstration of the influence of the photoperiod on the plasma concentration of the growth hormone in the ram].

The influence of photoperiod on GH release has been studied in Rams subjected to two different light regimes. The first group was submitted to natural daylight variations. The second group received daily the following split photoperiod: 7 L, 9 D, 1 L, 7 D, known to stimulate the release of prolactin. The experiment lasted 5 months, from January to June. In the first group, plasma GH concentrations decreased significantly from January to February (10.1 +/- 0.4 vs 8.7 +/- 0.3 ng X hr./ml; P less than 0.02), then increased from April to June (9.3 +/- 0.4 vs 10.5 +/- 0.7 ng X hr./ml; P less than 0.02). In the second group, GH concentrations were higher than in the first group in April (11.9 +/- 0.9 vs 9.3 +/- 0.4 ng X h/ml; P less than 0.05). However, it decreased between April and June (11.9 +/- 0.9 vs 9.7 +/- 0.4 ng X hr./ml; P less than 0.02) and then did not differ from that of the first group. These results show that plasma GH concentrations are affected by photoperiodic changes and suggest the existence of seasonal variations in GH plasma levels in the Ram.

Animals↗