Endocrinology
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The vasopressin-immunoreactive (AVP-ir) projections of the bed nucleus of the stria terminalis (BST) and medial amygdaloid nucleus (MA) are much denser in males than in females even if males and females are treated with similar amounts of testosterone. Previous studies have established that testosterone influences AVP-ir projections during development, but not whether these effects of testosterone were permanent. This study tested the effects of various hormonal manipulations during development on the ability of testosterone to influence the AVP immunostaining in cells of the BST and MA and of fibers in the lateral septum of adult rats. ⋯ This indicated that testicular secretions influenced the differentiation of AVP-ir pathways around postnatal day 7. This was further confirmed in the third experiment, in which testosterone propionate treatment at the seventh postnatal day significantly raised AVP-ir fiber density in the lateral septum of neonatally gonadectomized male and female rats and fully restored the number of AVP-ir cells in the BST of neonatally castrated males. Combined, these data suggest that testosterone levels around the seventh postnatal day determine the sexual differentiation of AVP-ir projections to the lateral septum.
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Galanin is colocalized with GnRH in neurons of the hypothalamus and basal forebrain of female rats, and this neuropeptide may play a role in the generation of the midcycle surge of gonadotropin secretion. We tested the hypothesis that galanin gene expression in GnRH cells increases during proestrus. To accomplish this, we killed groups of adult female rats at 1200 and 1800 h on the day of proestrus as well as at 1800 h on the day of estrus and used double labeling in situ hybridization and image analysis to estimate and compare the levels of galanin mRNA in cells coexpressing GnRH mRNA. ⋯ Here, we used single labeling isotopic in situ hybridization for GnRH mRNA and computerized image analysis to count the resulting silver grains. We could detect no difference in GnRH mRNA signal levels (proestrus, 1200 h vs. proestrus, 1800 h vs. estrus, 1800 h). In a final experiment, we investigated the possible role of estrogen in the induction of galanin mRNA expression at proestrus by comparing relative galanin mRNA contents in GnRH neurons among groups of ovariectomized, intact (diestrous day 1), and ovariectomized 17 beta-estradiol-replaced female rats.(ABSTRACT TRUNCATED AT 400 WORDS)
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Previous studies demonstrated that the polypeptide diazepam binding inhibitor (DBI) and its receptor, the peripheral-type benzodiazepine receptor (PBR), are involved in the regulation of steroid biosynthesis and that one site of PBR action resides in mitochondria. In the present investigation, evidence is presented that a functional form of PBR is also present at the cell surface. First, PBR was immunolocalized in the rat testis using biotin-streptavidin peroxidase immunocytochemistry, and results revealed that PBR was present exclusively in the interstitial Leydig cells. ⋯ We then examined the effects of DBI on Leydig cell function. DBI added to MA-10 cells affected DNA synthesis and cell growth in a biphasic manner; at low concentrations (1 nM), DBI was mitogenic, increasing [3H]thymidine incorporation and cell numbers by 30-40%, while at high concentrations (1 microM), DBI inhibited cell growth (30-40%). Similar effects on cell growth were obtained using the benzodiazepine Ro5-4864.
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Insulin secretion was studied in rat pancreatic islets after 24-h exposure to various glyburide or tolbutamide concentrations. Glucose-induced insulin release was significantly (P < 0.05) reduced in islets cultured with 0.1 microM glyburide or 100 microM tolbutamide (2098 +/- 187, 832 +/- 93, and 989 +/- 88 pg/islet.h in control, glyburide-exposed, and tolbutamide-exposed islets, respectively). When glyburide-treated islets were stimulated with glyburide or tolbutamide, insulin release was also impaired compared to that in control islets (P < 0.05). ⋯ Preexposure to 0.1 microM glyburide did not change calcium uptake at a glucose concentration of 2.8 mM (1.44 +/- 0.45 pmol/islet.2 min) but significantly reduced calcium uptake stimulated by 16.7 mM glucose (3.21 +/- 0.35 pmol/islet.2 min; n = 4; P < 0.005 compared to control islets). In contrast, preexposure to 100 microM tolbutamide did not change either basal or glucose-stimulated calcium uptake (1.44 +/- 0.45 and 6.90 +/- 0.81 pmol/islet.2 min, respectively; n = 4). These data show that in vitro chronic exposure of pancreatic islets to the sulfonylureas glyburide and tolbutamide impairs their ability to respond to a subsequent glucose or sulfonylurea stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)
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We have investigated the ACTH and cortisol responses to acute episodes of hypoxemia or hypoglycemia in fetal sheep in which the hypothalamus and pituitary were surgically disconnected at between 112 and 123 days gestation. Before 130 days gestation, basal plasma concentrations of ACTH were significantly greater in the hypothalamo-pituitary disconnected (HPD) fetuses than in the intact fetal sheep (126-130 days; 105.0 +/- 11.4 ng/liter, HPD group; 64.0 +/- 9.5 ng/liter, intact group). After 130 days, however, there was no difference between plasma ACTH concentrations in the HPD (136-140 days; 154.7 +/- 16.7 ng/liter HPD group; 113.6 +/- 19.1 ng/liter, intact group) and intact fetal sheep, and in both groups the mean ACTH concentrations were significantly greater after 136 days gestation than before 130 days. ⋯ In the HPD fetuses, however, there was no significant change in plasma ACTH concentrations during or after the insulin infusion. In both the HPD and intact groups, there was a significant increase in plasma ACTH concentrations above control values (62.5 +/- 8.5 ng/liter intact; 135.0 +/- 30.6 ng/liter, HPD) after intrafetal administration of CRF (+10 min; 117.5 +/- 8.1 ng/liter, intact; 225.3 +/- 33.1 ng/liter, HPD) indicating that the secretory capacity of the pituitary corticotrophs was not reduced by the HPD procedure. Our results demonstrate that an intact hypothalamic-pituitary connection is required to generate a normal prepartum increase in fetal cortisol concentrations and is essential for an appropriate fetal pituitary-adrenal response to intrauterine hypoxemia and hypoglycemia.