摘要:

The direct effects of median eminence extract (MEE), estradiol (E) or progesterone (P) or combinations of these hormone preparations on the structure of the adenohypophysis and its secretion of gonadotrophins were examined in female rats bearing pituitary homografts obtained from long-term ovariectomized (LTO) donors. Preliminary investigation had shown that the pars distalis of LTO animals retained large numbers of hypertrophied gonadotrophs for several weeks even when homografted under the kidney capsule of hypophysectomized recipients. Homografts from vehicle-treated controls contained many gonadotrophs at 24 days. Treatment with E or P resulted in complete disappearance of gonadotrophs at 24 days, but not at 10 days. E produced depletion of gonadotrophs even in the presence of MEE, while P + MEE treatment resulted in retention of gonadotrophs. In general, ovarian morphology correlated well with changes in pituitary cytology. These results suggest that the ability of MEE to stimulate release (and probably synthesis) of gonadotrophic hormones depends on the steroid sensitization of pituitary tissue and the differential effect of E and P on gonadotrophin release in the presence of MEE.

ISSN:0028-3835    

DOI:10.1159/000122461

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

The plasma corticosterone level was determined in chronic thalamic pigeons. Basal resting adrenocortical activity did not show any diurnal variation and kept a steady intermediate level. The peak and nadir in the morning and in the evening were completely suppressed. Neurogenic stress (restraint) resulted in a sharp increase in the plasma corticosterone concentration 15 min after immobilization. This response was as important in magnitude (three-fold the resting level) in thalamic pigeons as in intact birds. These results can be compared with data obtained after complete or partial deafferentation of the hypothalamus, and after hippocampal or archistriate lesions, and are discussed in terms of sleep-waking alternation in these various experimentally-prepared pigeons.

ISSN:0028-3835    

DOI:10.1159/000122462

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

Cycling was induced in old non-cyclic, constant estrous rats by daily injections of progesterone, ACTH or L-dopa or by subjection to ether stress. Progesterone and ACTH were the most effective agents used for re-establishing estrous cycles in these rats. Most of the progesterone- and ACTH-treated rats showed regular cycles, and their ovaries had many corpora lutea; they also showed proestrous serum LH surges. Ether stress and L-dopa mostly induced irregular cycles and fewer corpora lutea in the ovaries; a smaller number of these rats showed proestrous LH surges. After treatment with each of these agents was discontinued, most of the rats returned to constant estrus or irregular cycling.

ISSN:0028-3835    

DOI:10.1159/000122463

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

In order to clarify the role of cyclic nucleotides in the mediation of LH-releasing hormone (LH-RH) action on LH release, the effect of LH-RH on LH release and pituitary cyclic AMP and cyclic GMP accumulation was studied in vivo. Pituitary cyclic AMP levels were increased 10 min after the intravenous injection of 2 mg dibutyryl cyclic AMP (db-cyclic AMP) or 25 mg aminophyllinε. However, serum LH levels were not altered at 10, 30 or 60 min after the administration of either agent. Synthetic LH-RH (100 ng/rat) increased serum LH levels as measured 10 min after injection, but no effect on either pituitary cyclic AMP or cyclic GMP was seen 1, 5 or 10 min after LH-RH administration. These in vivo results are con t adictory to the second messenger hypothesis for either cyclic AMP or cyclic GMP in the mediation of LH-RH-induced LH release and suggest that further work must be done in order to confirm or reject this hypothesis.

ISSN:0028-3835    

DOI:10.1159/000122464

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

The effect of breast feeding on serum FSH and LH concentrations was studied in 13 puerperal women. Despite the collateral increase in serum prolactin levels, nursing was not followed by significant changes in serum FSH or LH levels during a 30-min observation period. Our data indicate that nursing has no significant effect on pituitary FSH and LH release.

ISSN:0028-3835    

DOI:10.1159/000122465

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

L-Dihydroxyphenylalanine (L-DOPA)significantly inhibited intrathyroidal colloid droplet formation induced by exposure to cold in the rat. Diethyldithiocarbamate (DDC) also inhibited colloid droplet formation in response to cold. The combined administration of L-DOPA and DDC produced an additive inhibition of the thyroidal endocytotic response to exposure to cold. Pretreatment with chlorpromazine (CPZ) ameliorated the inhibitory effect of (L-DOPA)DL-alpha-methyl-p-tyrosine (α-MT) also significantly depressed the thyroidal response. Inhibition of colloid droplet formation induced by α-MT was not altered by the administration of DL-dihydroxyphenylserine (DL-DOPS). On the other hand, treatment of the α-MT-treated rats with L-DOPA to normalize dopamine synthesis resulted in a dramatic recovery from the inhibition. Blockade of serotonin biosynthesis with p-chlorophenylalanine (p-CPA) failed to produce a significant inhibition of colloid droplet formation. However, 5-hydroxytryptophan (5-HTP) markedly inhibited the thyroidal response to cold. Brocresine phosphate (BP) was another inhibitor of the thyroidal endocytotic response to exposure to cold. Oxotremorine also markedly depressed the thyroidal response to cold. Since these drugs did not interfere with pituitary-thyroid responsiveness to exogenous thyrotropin-releasing hormone (TRH), it seems that the thyroidal endocytotic response to exposure to cold as a reflection of TSH secretion was directly influenced by alterations of brain biogenic amine concentrations or turnover rat

ISSN:0028-3835    

DOI:10.1159/000122468

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

Neurosecretory axo-axonic synapses were found in the median eminence of the turtle. Most of the presynaptic axons contain granules approximately 95 nm in diameter, and the postsynaptic elements have granules approximately 110 nm in diameter. The functional significance of axo-axonic synapses in the median eminence is discussed in relation to the discharge of releasing hormones from the axon terminals.

ISSN:0028-3835    

DOI:10.1159/000122469

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

The influence of the hippocampus upon pituitary release of adrenocorticotropic hormone (ACTH) was studied in male Sprague-Dawley rats which had concentric bipolar stainless steel electrodes chronically implanted in the dorsal and ventral hippocampus. Blood samples were withdrawn at half-hour intervals from a cannula in the right atrium. Plasma corticosterone levels reflected ACTH release. 30 min of 25 or 250-cps electrical stimulation of the hippocampus in the freely-behaving, non-stressed rat resulted in significant increases in basal plasma corticosterone levels evident at the end of stimulation. In afternoon experiments, after stimulation at either hippocampal site with 25 cps only, the increase was followed by a delayed inhibitory phase and temporary inhibition of the circadian rise in corticosterone levels. The inhibitory effect was more pronounced with ventral than with dorsal hippocampal stimulation. The basis for these differential effects is discussed in terms of the anatomical organization of the hippocampus.

ISSN:0028-3835    

DOI:10.1159/000122470

出版商:S. Karger AG    

年代:1976

数据来源: Karger

摘要:

Studies were made to test the responsiveness of dispersed pars intermedia (PI) cells to a number of secretagogues that are known to alter ACTH release from the pars distalis (PD) in vitro. In summary, (a) incubation in high [K+], which will increase ACTH release from the PD, did not alter ACTH release from the PI; (b) a crude extract of rat hypothalamus (HE) increased ACTH release from PD and PI; (c) the effect of HE was not due to its vasopressin content, since pretreatment of the extract with thioglycolic acid did not modify its ACTH-releasing activity and neither lysine nor arginine vasopressin stimulated ACTH release from the PI; and (d) a partially purified CRF preparation, which will stimulate ACTH release from the PD, did not alter ACTH release from the PI. We conclude that the hypothalamus contains a substance(s) that will stimulate ACTH release from the PI and that the ‘secretagogue’ is neither vasopressin nor the same CRF that will stimulate ACTH release from the

ISSN:0028-3835    

DOI:10.1159/000122471

出版商:S. Karger AG    

年代:1976

数据来源: Karger