摘要:

Administration of αMT to inhibit catecholamine synthesis or dopamine (DA) receptor blockade with spiroperidol had no effect on the hypothalamic concentration of 5HT or 5HIAA. Fluoxetine to block serotonin uptake had no influence on the elevation of serum prolactin levels induced by αMT or DA receptor blockers and conversely «MT did not influence the prolactin-releasing action of 5HTP alone or in combination with fluoxetine. Depletion of brain serotonin stores with p-chlorophenylalanine did not affect the prolactin-releasing action of «MT or DA receptor blockers. In contrast, the serotonin blocker methysergide, but not cyproheptadine, inhibited the prolactin-releasing effect of αMT or α-flupentixol, a DA receptor blocker, but not of spiroperidol, another DA receptor blocker. The intensity of the inhibition induced by methysergide paralleled the intensity of inhibition induced by apomorphine. Methysergide conspicuously lowered serum prolactin in animals with electrolytic destruction of the median eminence, whereas cyproheptadine had only a slight effect. The prolactin-inhibiting effect of methysergide could be prevented by pretreatment of the lesioned rats with spiroperidol. It is concluded that elimination of the influence of the DA system does not activate the central serotoninergic system; that activity of the serotoninergic system has no role in the activation of prolactin secretion induced by suppression of the inhibitory dopaminergic influence, and that the inhibiting action of methysergide on the prolactin-releasing effect of αMT or α-flupentixol is due to its dopamine receptor agonist activity rather than to blockade of serotonin re

ISSN:0028-3835    

DOI:10.1159/000122988

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

A heterologous radioimmunoassay for canine prolactin was developed and used to study the role of catecholamines and indoleamines in the regulation of prolactin secretion in dogs. Female dogs were found to have a higher plasma prolactin concentration than male dogs. Thyrotropin-releasing hormone (TRH) increased plasma prolactin in male and female trained conscious dogs. L-Dopa blocked the increase produced by TRH, but this effect could be reversed by pretreatment with carbidopa, an inhibitor of the conversion of L-dopa to catecholamines outside the blood-brain barrier. The intravenous administration of the immediate precursor of serotonin, L-5-hydroxytryptophan (5HTP), caused an increase in plasma prolactin and growth hormone. The administration of the serotonin receptor blocker, metergoline, 18 and 3 h before 5HTP, significantly augmented the growth hormone response to 5HTP. In contrast, metergoline diminished the prolactin response to 5HTP. Pretreatment with carbidopa did not change the prolactin or growth hormone responses to 5HTP. These observations indicate that the dog is similar to other mammals in that females have greater plasma prolactin concentrations than males and TRH increases plasma prolactin. L-Dopa appears to act at a site outside the blood-brain barrier to prevent the prolactin response to TRH. The data suggest that 5HTP increases plasma prolactin via a serotonergic mechanism, whereas it increases plasma growth hormone via a different, nonserotonergic mechanism.

ISSN:0028-3835    

DOI:10.1159/000122989

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Female Wistar rats treated with a single subcutaneous injection of 2 mg estradiol valerate (EV) develop gradually progressive, multifocal lesions of the arcuate nucleus. They also exhibit persistent vaginal estrus and endocrine profiles characteristic of animals sustaining anterior hypothalamic deafferentation. In this study, EV-treated females with the arcuate lesions released significantly less LH 1 h following electrochemical stimulation of the medial preoptic area (MPOA) than did normally cycling controls in proestrus. FSH release in response to MPOA stimulation was the same for both groups. As plasma LH concentrations were not significantly different between EV-treated and control animals 1 h after the injection of a potent LHRH analog, the reduced LH response to MPOA stimulation appears to reflect a primarily hypothalamic defect. However, the EV treatment also affected pituitary responsiveness to long-term stimulation as evidenced by reduced LH responses to the LHRH analog after 2 and 3 h. No such differences were seen in the FSH response.

ISSN:0028-3835    

DOI:10.1159/000122990

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The paraventricular nucleus of the rat hypothalamus has been shown to project to the medulla and spinal cord. The proportion of oxytocin-neurophysin (OTNP) axons to vasopressin-neurophysin (VPNP) axons in these structures is unknown. A major difficulty in resolving this problem in previous immunocytochemical studies was the lack of a specific antiserum to each rat neurophysin. In this study two approaches have been used: (1) comparison of immunostaining for neurophysin in normal versus homozygous Brattleboro rats with diabetes insipidus (HODI) which lack VPNP, and (2) application of an antiserum to both rat neurophysins absorbed with HODI rat hypothalamic-pituitary extracts which contain only OTNP. The latter would result in an antiserum specific for VPNP. Our results indicate that the axons which constitute the caudal projections from the paraventricular nucleus are predominately oxytocinergic, the vasopressinergic innervation being limited to the nucleus tractus solitarius, the dorsal motor nucleus of vagus, and the substantia gelatinosa. A similar number of reactive fibers were seen in the medulla and spinal cord of normal and HODI rats. No positive perikarya were observed caudal to the hypothalamus. Fibers in the medulla appeared to terminate in the nucleus of the solitary tract and in the dorsal motor nucleus of the vagus nerve. Positive fibers throughout the cord were present in the substantia gelatinosa and in the intermediolateral grey. The possible role(s) of these projections in integrating autonomic functions and afferent information with neuroendocrine regulation is discussed.

ISSN:0028-3835    

DOI:10.1159/000122991

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Pseudopregnancy inhibited plasma i corticosterone response to stress. The production of corticosterone by adrenal slices in vitro was also decreased; no changes in adrenal 5α-reductase activity were observed. Secretion of corticosterone in the adrenal venous blood was decreased as well, without changes in dehydrocorticosterone or tetrahydrocorticosterone secretion rates. Treatment with ACTH increased the secretion rates of corticosterone to the range observed in control rats. Steady state secretion and metabolism of corticosterone were unchanged. The data indicate that the diminished responses in plasma concentrations, in vitro production, and secretion rates of corticosterone obtained in pseudopregnant rats after stress, are secondary to changes on the release of ACTH from the pituitary gland rather than to adrenal steroid secretion per se or handling of corticosterone by the liver. The expected rise in plasma prolactin observed in cycling rats after stress was absent in pseudopregnant rats. The data suggest that an inhibition of the prolactin release mechanisms similar to that observed with the release of ACTH may have occurred after stress. The dynamics involved in the changes affecting the release of pituitary hormones in pseudopregnant rats are still unclear

ISSN:0028-3835    

DOI:10.1159/000122992

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Incubated pituitary halves from ovariectomized, estrogen-implanted female rats were shown to be much more sensitive to LHRH than pituitaries from castrated, nontreated animals. LHRH in a concentration of 1,885 pg/ml increased the release of LH and FSH from 7.3 ± 0.9 and 0.91 ± 0.13 ng/h/hemipituitary respectively to 21.4 ± 1.9 and 1.97 ± 0.18 ng/h in animals implanted with the steroid. In contrast, 5,000 pg/ml of LHRH increased LH secretion from 3.4 ± 0.3 to 8.4 ± 0.4 ng/h in ovariectomized, nontreated animals. In pituitaries from both steroid and nontreated animals a highly significant dose response for LH and FSH secretion to the actual concentration of LHRH measured in each incubation tube by radioimmunoassay was observed. When expressed as percent of the corresponding control release, maximal stimulation of LH and FSH was comparable. Pituitaries from implanted animals provided a very sensitive bioassay for LHRH, in which amounts of the peptide lower than 100 pg/ml were detected. The apparent responsiveness to LHRH of pituitaries from estradiol-treated rats was found to be over 20 times greater than that of pituitaries from nontreated cast

ISSN:0028-3835    

DOI:10.1159/000122993

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

23-day-old male rats were left intact, rendered blind and anosmic, pinealectomized together with blinding and anosmia, or subcutaneously implanted with graded doses of melatonin in beeswax immediately following surgical blinding and anosmia. 5 weeks later, blind, anosmic animals were found to have significantly depressed anterior pituitary, testicular, and accessory sex organ weights. Both pituitary and plasma prolactin and luteinizing hormone (LH) concentrations were also significantly suppressed. Pinealectomy of blind, anosmic animals completely restored testicular and accessory organ weights. Likewise, pituitary LH and prolactin and plasma LH levels were also restored to intact control levels by pineal removal. Only the highest dose of melatonin (1 mg) restored the testicular and accessory sex organ weights to those of the intact controls. As little as 1 μg melatonin restored plasma and pituitary LH concentrations to the levels of the intact controls. However, none of the dosages of melatonin reversed plasma prolactin concentrations to those of the untreated animals. The decrease in pituitary prolactin induced by blinding and anosmia was reversed by pinealectomy or by the lower doses (1, 50 or 100 μg) of melatonin. These results indicate that melatonin implants can reverse the antigonadotrophic effects of blinding and anosmia in male rats. The minimal dose of melatonin required to restore testicular and accessory sex organ weights in blind, anosmic rats is 1 mg implanted subcutaneously in beeswa

ISSN:0028-3835    

DOI:10.1159/000122994

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The effects of subcutaneous injections of vasopressin on the passive avoidance behavior of rats were investigated in an extensive study. 200 male Wistar rats were tested in a step-through passive avoidance task. The animals were assigned randomly to 1 of 20 experimental groups consisting of five vasopressin injection and four shock level conditions. Each animal was trained to enter a dark compartment, then subjected to 0.25, 0.10, 0.05 mA or no foot shock for 2 sec. 60 min prior to a retention test administered 24 h after the foot shock, each animal was given a single injection of 0.30, 0.12, 0.06, or 0.03 IU of vasopressin or of saline. Time to reenter the shock compartment was tested 24 and 48 h after the foot shock. Latencies in both retention tests indicated that, although there was a significant effect of shock level on latency scores, there was no effect of vasopressin with any dose level tested. The inability to find an effect of vasopressin in this study is contrary to results of other studies. Several factors, including general reactivity of the animals or the distribution system for vasopressin in the brain, might provide the underlying reason for these dramatic differences.

ISSN:0028-3835    

DOI:10.1159/000122995

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Incubation of anterior pituitary (AP) fragments of rats was used to determine the specific role played by vasopressin (VP) in the overall effect of crude hypothalamic median eminence (HME) extract on ACTH release. Using the property of an AVP antiserum (AS) to completely abolish the CRF-like effect of hypothalamic VP without apparently affecting the effect of CRF, we show that under specific incubation conditions, the effect of the two secretagogues are additive at the pituitary level. ACTH secretion of pituitaries was enhanced when incubation was carried out in the presence of VP together with a maximum effective dose of VP-free HME extract (from Brattleboro rats). These observations favor the hypothesis that VP and CRF have different receptor sites in the anterior pituitary.

ISSN:0028-3835    

DOI:10.1159/000122996

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

In male rats, serum testosterone (T) and progesterone (P) levels fluctuate with daily periodicities that appear to be inversely related. To further investigate this interrelationship between serum T and P levels, we studied the effects of exogenous P on serum androgen levels. At 6–8 h after administration of P, serum T and DHT levels were consistently increased without any alterations in the serum LH and FSH levels. Following disruption of the hypothalamo-pituitary-adrenal axis either by adrenalectomy or by anterior hypothalamic deafferentation, procedures known to abolish serum T and P periodicities, P was again effective in raising serum T concentrations without altering the serum gonadotropin values. These results show that P may directly enhance testicular secretion, and thus support the possibility that the observed adrenal influence on daily testicular T secretion pattern may be hormonally mediated via P secretio

ISSN:0028-3835    

DOI:10.1159/000122997

出版商:S. Karger AG    

年代:1980

数据来源: Karger