摘要:

In order to assess the possible involvement of central cholinergic mechanisms in the feedback actions of gonadal hormones, the activity of choline acetyltransferase (ChAT) and the concentration of acetylcholine (ACh) were measured in microdissected brain nuclei of male and female rats after castration and gonadal hormone replacement. Castration of male rats significantly elevated plasma levels of LH and also increased ChAT activity and ACh level in the medial preoptic nucleus. Castration also increased ChAT activity but not ACh concentration in the posteromedial amygdala. In the rostral part of the nucleus tractus diagonalis and in the ventral tegmental area. ACh concentrations were elevated by castration, but ChAT activity was unaffected. Daily administration of testosterone propionate (TP) to castrated males attenuated the postcastration rise of plasma LH and also partially prevented the increases of ACh in the medial preoptic and rostral tractus diagonalis nuclei and of ChAT in the posteromedial amygdala. In addition, TP treatment significantly decreased ChAT acivity in the rostral nucleus tractus diagonalis. Treatment of ovariectomized female rats with estradiol benzoate lowered plasma levels of LH, but did not affect cholinergic parameters. Administration of progesterone to estrogen-primed females produced a surge in plasma LH and decreased the activity of ChAT and the concentration of ACh in the periventricular nucleus. Such treatment also reduced ChAT activity in the caudal nucleus tractus diagonalis and decreased ACh levels in the ventral tegmental area. The combined estradiol/progesterone treatment elevated ChAT activity in the supraoptic nucleus. These results demonstrate that cholinergic activity in several discrete brain regions known to be targets for testicular and ovarian hormones is altered by gonadectomy and gonadal hormone treatment and suggest involvement of cholinergic systems in the feedback effects of estadiol, progesterone and testosterone.

ISSN:0028-3835    

DOI:10.1159/000123024

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

To determine the involvement of the midbrain in the control of the proestrous surge of gonadotropins and prolactin, various transections were acutely placed in proestrous rats. Half-dome shaped transections which interrupted the neural fibers in the ventromedial part of the midbrain (VMM transection), as well as lesions in the ventral tegmental area, blocked ovulation and the proestrous surges of gonadotropins and prolactin whereas sham transections or the other transections, either dorsal or lateral to VMM transections, had no effect on ovulation. VMM transections, however, affected neither the postcastration rise in serum gonadotropins in males nor the secondary rise in serum FSH in estrous females. These results suggest that in the ventromedial part of the midbrain there exists a common neural mechanism which controls the proestrous surges of gonadotropins and prolactin.

ISSN:0028-3835    

DOI:10.1159/000123025

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The existence of typical muscarinic receptors in membranes of sheep anterior pituitary was detected by binding of [3H]quinuclidinyl benzilate ([3H]QNB), a potent and specific muscarinic antagonist. [3H]QNB binding sites in anterior pituitary had an equilibrium dissociation constant of about 20–40 pM, a rate constant for association at 37 C of about 2 × 108M–1 min–1, a rate constant for dissociation at 37 C of about 4 × 10–3 min-1 and the expected specificities for a variety of choiinergic and other drugs. The concentration of [3H]QNB binding sites in anterior pituitary, about 4–6 pmol/g tissue, was at least twice that in posterior pituitary, but less than a quarter that in the hypothalamus. Since there is no established choiinergic or other innervation of the anterior pituitary, the presence there of typical muscarinic receptors, if we assume that they are functional, suggests that acetylcholine reaches the tissue through the hypophyseal portal circulation, and that it may thus have a role in the regulation of pituita

ISSN:0028-3835    

DOI:10.1159/000123026

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The neuraliy depressant amino acid taurine and related metabolites were tested for their ability to alter prolactin (PRL) secretion in conscious, unrestrained male rats. The intraventricular infusion oftaurine (0.2 and 2.0 μmol) elicited a significant increase in PRL secretion. Hypotaurine (0.2 and 2.0 μmol), cysteic acid (2.0 μmol), mannitol (2.0 μmol) and 0.9% saline were ineffective in altering PRL secretion. When infused directly into the pituitary of conscious, unrestrained male rats none of the substances tested stimulated PRL secretion. Taurine (50.0 μmol) was similarly ineffective in stimulating PRL secretion when an in vitro pituitary preparation was used. These studies indicate that taurine is capable of stimulating PRL secretion in the male rat. This effect appears to be mediated centrally, presumably at the hypothal

ISSN:0028-3835    

DOI:10.1159/000123027

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The effects of neutralized acid extracts of rat hypothalami (HE) on the release of bioactive and immunoactive rat growth hormone (GH) were investigated in 4 in vitro experiments. In 2 short-term incubations and in a 3-day organ culture, HE from hypophysectomized rats stimulated the release of biologically active GH from rat adenohypoph-yses, whereas the radioimmunoassay (RIA) recorded increased GH secretion by HE in only 2 of the experiments, and to a lesser degree. Addition of HE to secreted GH strongly inhibited the response of the bioassay animals to the GH, while it had no effect on the measurement of the hormone in the RIA, suggesting that the discrepancies between the amounts of bio- and immunoactive GH secreted as a result of HE were even greater than our assays recorded. The possibility that the inhibition of the measurement of GH in the bioassay was due to low molecular weight substances was tested in an additional short-term incubation experiment. HE from intact rats caused no stimulation of GH release as measured by either assay. Dialysis caused a loss of RIA-detectable GH by about 35% in both the control and HE-containing media, while it had no effect on bioactive GH in control medium. Dialysis did enhance the biological GH activity of the HE medium, however. Thus, a dialyzable material present in HE was interfering with the response of the bioassay animals to GH. These results support other evidence for the differential release of rat GH with varying immuno- and bioactivities and indicate that HE contains low molecular weight substance(s) that inhibit the tibial growth response in hypophysectomized rats to GH.

ISSN:0028-3835    

DOI:10.1159/000123028

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Repeated infusions of 6-hydroxydopamine (6-OHDA) into the third ventricle of the rabbit brain in dosages shown to depress hypothalamic norepinephrine (NE) by more than 80% failed to block the copulation-induced ovulatory surge of LH release from the adenohypophysis in estrogen-primed, multiparous New Zealand White does. Only when infusion of the neurotoxin produced a basal hypothalamic lesion did it intercept the coital stimulus and prevent LH release. In 5 rabbits the initial infusion of 6-OHDA stimulated an LH surge presumably by activating NE release from noradrenergic nerve endings. The failure of chronic depletion of hypothalamic NE to prevent coitally-induced LH release suggests that the transmitter may normally play only a modulatory role in hypothalamopituitary activation in the reflex ovulator, as has also been proposed for its function in cyclic ovulation in the rat. The results suggest that alternative systems may be brought into play to subserve reproductive mechanisms when hypothalamic NE is chronically depleted.

ISSN:0028-3835    

DOI:10.1159/000123035

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Ovariectomized female rats were implanted with estradiol containing silastic implants to induce constant circulating levels of the steroid, and sacrificed every 2 h in order to determine neuroendocrine rhythms. Under these conditions, we observed very marked circadian fluctuations in the hypothalamic concentrations of corticotropin-releasing factor (CRF). luteinizing hormone-releasing hormone (LHRH) and thyrotropin-releasing hormone (TRH), and in plasma levels of adrenocorticotropin (ACTH), corticosterone, luteinizing hormone (LH) and prolactin; the amplitude of the prolactin cycle was in particular much higher than in non-chronically estrogenized animals. The daily variation in CRF, ACTH and corticosterone showed significant rank correlations. Changes in hypothalamic content of LHRH and TRH were biphasic; the increase observed during the light period was abruptly interrupted by a depletion episode, coincident with the period of maximal LH and prolactin secretion, respectively. The initial phase of ACTH, LH and prolactin increments occurred between 11.00 and 15.00 h, and was relatively well synchronized. The steepest rise in ACTH and prolactin occurred at the same time, and preceded that of LH by a constant lag of about 2 h. After that initial period, secretion kinetics of the three hormones followed an independent pattern. The data suggest that increased secretion of several hormones results from activation of neural mechanisms occurring within a limited period of the 24-hour cycle.

ISSN:0028-3835    

DOI:10.1159/000123029

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

H-Pro-Leu-Gly-NH2 (PLG) was labeled with 3H-leucine by catalytic tritiation of H-Pro-methylallylglycyl-Gly-NH, and purified by ion-exchange chromatography. Metabolism of 3H-PLG in rat and human plasma was investigated by reversed phase-paired ion high-pressure liquid chromatography. All possible metabolites could be completely separated within 25 min. Half-lives, based on disappearance of intact 3H-PLG, for in vitro metabolism were 26.4 min (rat) and 5.6 days (human). The only significant metabolite was 3H-leucine. A rate-limiting, species-specific enzyme seems responsible for the initial breakdown of PLG. Disappearance of 3H-PLG from rat plasma, following i.v. administration, proceeded with half-lives of 1.03 min (distribution) and 9.8 min (elimination).

ISSN:0028-3835    

DOI:10.1159/000123030

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

A procedure is described for collection of blood from the confluens sinuum of the rat. Melatonin concentration, measured by RIA, in plasma of the confluens was found to be significantly higher than that in peripheral plasma. Melatonin levels in cerebrospinal fluid of the cisterna magna were always lower than those in plasma and exhibited no significant changes which paralleled those occurring in plasma with darkness. It is concluded that, in the rat, the major route of secretion of melatonin by the pineal gland is into the blood of the confluens sinuum.

ISSN:0028-3835    

DOI:10.1159/000123031

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Administration of the antiestrogen tamoxifen to normal Buffalo female rats caused a 45% reduction (p < 0.01) in 3H-prolactin synthesis and release in vitro. Radioimmunoassayable prolactin in incubated glands and medium also decreased significantly. Similar results were observed in Wistar-Furth animals except for in vitro radioimmunoassayable prolactin, which decreased less markedly (by 33%, p < 0.01). Serum prolactin concentration in treated rats was unchanged. Tamoxifen did not affect the extremely high serum prolactin concentration in rats bearing mammotropic tumors. It further reduced in vitro synthesis of radioactive prolactin but not of the radioimmunoassayable hormone. No interaction between antiestrogens and the dopamine agonist bromocriptine was observed. These observations suggest that the nonsteroidal antiestrogens decrease the synthesis of prolactin but have little effect on release of the hormone. Tamoxifen inhibits growth of transplantable mammotropic tumors MtTW15 and 7315a potently without altering tumor prolactin production. In vivo treatment of adult female rats with tamoxifen did not affect in vitro synthesis and release of radioactive growth hormone, but reversed the elevated growth hormone production of rats bearing 7315a tumors.

ISSN:0028-3835    

DOI:10.1159/000123032

出版商:S. Karger AG    

年代:1980

数据来源: Karger