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SUMMARY
The effect of cortisol (5 mg./100 g. body weight administered for 10 days) on the secretion of growth hormone (GH) from the pituitary was studied in 30-day-old female rats. The results indicate that the suppressive action of cortisol on GH secretion is not due to a reduced availability of the hormone in the pituitary but to an impairment of the release mechanism(s) as shown by the lack of GH release in response to insulin hypoglycaemia and by the marked decrease of GH-releasing activity in the hypothalamus of cortisol-treated rats.
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SUMMARY
The gonadotrophin-releasing activity of hypothalamo-neurohypophysial hormones has been investigated in normal female rabbits. Pooled urine, obtained before and after intravenous injection of different posterior pituitary preparations (Pitressin, Pitocin, lysine-vasopressin and synthetic oxytocin), was extracted by the kaolin-acetone method and assayed by the mouse uterus test. All the posterior pituitary preparations used induced a significant rise in the release of gonadotrophins.
The experiments suggest that posterior pituitary polypeptides may play a role in the physiological regulation of gonadotrophin release.
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SUMMARY
It is shown that anterior pituitary tissue grafted into hypophysectomized rats and lacking any connexion with the median eminence does not retain any somatotrophic or gonadotrophic activities, but has some adrenocorticotrophic (ACTH) and thyrotrophic (TSH) activities. This conclusion is based on: (1) the partial maintenance of thyroid and adrenal weight; (2) the results of studies on 131I uptake and on TSH concentration in the grafted pituitaries; (3) the persistence of significant adrenocorticotrophic responses to Pitressin, lysine-vasopressin and Guillemin's fraction D; (4) the presence of histological and histochemical signs of activity in the grafted gland.
The subnormal levels of secretion observed in the pituitary grafted into sites far removed from the sella turcica, seem to depend on the lack of some neurohumoral stimulus which normally activates the intact pituitary via the hypophysio-portal vessels.
Evidence is given that vasopressin may be the hypothalamic neurohumor involved in ACTH secretion, and that the ACTH-releasing activity of Guillemin's fraction D may be accounted for by its vasopressin content.
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SUMMARY
Injections of insulin (0·2 or 0·01 i.u./20 μl) into the lateral ventricle of the rat brain, while not changing blood glucose levels or altering the pituitary content of growth hormone (GH), blocked the release of GH from the pituitary and the decrease of growth-hormone releasing activity (GHRF) of stalk median eminence (SME) extracts in the presence of the hypoglycaemic effect on insulin (2 i.u./kg) given intraperitoneally. Intraventricular administration of insulin also impaired the GH release elicited by cold exposure (4 °C, 1 h) but not the release induced by electric shock. The possibility that insulin injected into the brain acts on glucose-sensitive GH-regulating structures is suggested.
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SUMMARY
The neurohaemal part of the median eminence of the rat hypothalamus is characterized by numerous nerve terminals which end near a rich network of fenestrated capillaries. An attempt was made to isolate different types of nerve terminals by means of sucrose density-gradient centrifugation. The subcellular fractions obtained were assayed for dopamine, noradrenaline and 5-hydroxytryptamine. In addition FSH- and GH-releasing activities were determined. A sample of each fraction obtained was taken for electron microscopical observations.
Dopamine, noradrenaline, 5-hydroxytryptamine, GH- and FSH-releasing factors were present in higher concentration in the nerve endings. A further fractionation showed that noradrenaline was present in the lightest synaptosomal band, dopamine in the middle one, and 5-hydroxytryptamine in the heaviest. GH-RF and FSH-RF were recovered mainly from the band containing dopamine. The relevance of this localization to the physiological role of the median eminence is discussed.
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Abstract
This study was undertaken to assess the sensitivity of hydroxylysylpyridinoline (HP), lysylpyridinoline (LP), galactosylhydroxylysine (GHyl) and glucosylgalactosylhydroxylysine (GGHyl) to monitor bone response to estrogen deficiency and replacement by comparing their excretory patterns in ovariectomized aged (11–14 months old) rats. The ovariectomized (OVX) rats were randomized into two groups: (1) OVX plus vehicle; (2) OVX plus 17β-estradiol (17-βE, 10 μg/kg, s.c., 4 days/week). Treatment with 17-βE started immediately after OVX and continued for 60 days. The collagen catabolites were measured in urine for 1 month before OVX and thereafter for 60 days. In temporal coincidence with urine collection, bone area and bone mineral density (BMD) of lumbar vertebrae, femoral diaphysis and distal metaphysis were measured by dual-energy X-ray absorptiometry. In the untreated rats, BMD of the femoral metaphysis and lumbar vertebrae decreased significantly and the urinary excretion of LP, HP, GHyl and GGHyl increased with different patterns. In the treated rats, 17-βE replacement prevented the increment in LP excretion, partially prevented the increase in HP excretion, but had no effect on the excretion of GHyl and GGHyl. In conclusion pyridinolines and glycosides have different sensitivities to the bone response to OVX. Glycoside excretion after OVX also reflects metabolic processes not strictly related to bone loss and, in contrast with LP, is not sensitive to estrogen replacement.
Journal of Endocrinology (1996) 150, 383–390
