摘要:

Dietary restriction reduces circulating gonadotropin and testosterone levels in male rats, an effect thought to be mediated through reduced gonadotropin-releasing hormone (GnRH) secretion; however, the cellular mechanisms subserving this response are still unknown. We reasoned that if dietary restriction reduces GnRH secretion, this would be reflected by a decrease in GnRH synthesis and likewise cellular GnRH mRNA levels. We tested this hypothesis by comparing cellular levels of GnRH mRNA between ad libitum fed (n = 4) and starved (n = 4) adult male rats. Five days of starvation resulted in a 21% decrease in body weight and an 85% decline in serum testosterone levels (fed: 13.9 ± 2.00 vs. starved: 2.1 ± 0.70 nmol/l; p < 0.01). In situ hybridization and image analysis demonstrated that short-term starvation influenced neither GnRH cell number (fed: 148 ± 16 vs. starved: 157 ± 13 cells) nor cellular GnRH mRNA signal level (fed: 177 ± 5 vs. starved: 160 ± 7 grains/ cell) in any region of the basal forebrain. Endogenous opioid peptides are known to exert an inhibitory effect on GnRH secretion and have been implicated in having a role in the starvation-induced effects on the reproductive system. We therefore also tested the hypothesis that alterations in pro-opiomelanocortin (POMC) gene expression are involved in the neuroendocrine response to starvation, by comparing cellular POMC mRNA levels in individual neurons (≈160 neurons/animal) of the arcuate and periarcuate nuclei between fed control (n = 4) and starved (n = 4) adult male rats. In contrast to the lack of effect on GnRH mRNA, starvation induced a 24% decline in cellular POMC mRNA signal levels (fed: 108 ± 6 vs. starved: 82 ± 5 grains/cell; p < 0.05), which was most pronounced in the anterior aspect of both the arcuate and periarcuate nuclei. Based on these results we conclude that (1) alterations in GnRH gene expression do not play a significant role in the suppression of gonadotropin secretion during food restriction, and (2) starvation causes a reduction in brain POMC gene expression, an effect possibly mediated by reduced circulating testostero

ISSN:0028-3835    

DOI:10.1159/000126324

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The effect of estrogen on the responsiveness of the luteinizing hormone-releasing hormone (LHRH) neurosecretory system to neuropeptide Y (NPY) stimulation was examined using a push-pull perfusion method in conscious monkeys. NPY, at doses of 10–6 to 10–12M, was infused into the stalk-median eminence (S-ME) of ovariectomized monkeys with or without estrogen, while perfusates were continuously collected. LHRH in perfusates was measured by RIA. The results indicate that in both estrogen-primed and unprimed monkeys, NPY infusion into the S-ME elicited LHRH release in a dose-dependent manner (p < 0.01). Moreover, estrogen priming enhanced the responsiveness of LHRH release to NPY infusion: (1) the minimum NPY dose necessary to elicit a significant LHRH response was reduced, (2) the peak LHRH response to NPY at a dose of 10–6 to 10–10M was increased, and (3) the total release of LHRH in response to NPY at doses of 10–6 to 10–12M was increased. These results suggest that NPY stimulates LHRH release in the S-ME in the presence or absence of estrogen and that estrogen enhances the responsiveness of the LHRH neurosecretory system to NPY stimulation in the rh

ISSN:0028-3835    

DOI:10.1159/000126325

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

The levels of specific soluble aspartyl aminopeptidase activity were assayed in retina, occipital cortex, anterior pituitary, posterior pituitary, pineal gland and serum of adult male rats, using Asp-2-naphthylamide as substrate, in a 12:12 h light:dark cycle (7–19 h light). Significant diurnal variations appeared in retina, pineal gland, occipital cortex and serum. In addition, different patterns of diurnal variation of the enzymatic activity were observed in the tissues analyzed. A regular increase of the activity was noticed at the end of the dark period in all the tissues as a common feature, except in serum, in which the enzymatic activity reached a peak in the middle of the light period, decreasing progessively during the dark hours. After the last hours of darkness, the pattern of variation in the activity differed in each tissue. These diurnal variations in aspartyl aminopeptidase activity could reflect the functional status of its putative endogenous substrates, such as angiotensin II, and it may also suggest the existence of differential regulatory mechanisms associated with each locatio

ISSN:0028-3835    

DOI:10.1159/000126326

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

To examine the role of neuropeptide Y (NPY) in the regulation of puberty, the effects of various doses of NPY or saline injected into the 3rd ventricle of peripubertal female rats were determined. A single injection of NPY at a dose range of 10-20 µg into the 3rd ventricle of 30-day-old female rats advanced the time of vaginal opening (VO) and first ovulation by 4 days, as compared to saline-treated controls. Ova number and ovarian, adrenal and uterine weights at first estrous were similar in all animals regardless of treatment. The NPY-treated precocious animals showed lower body weight than did the VO-matched controls, but showed similar body weight as that of age-matched controls. Determination of plasma luteinizing hormone (LH) levels in the peripubertal female rats revealed that plasma LH was increased transiently immediately after NPY administration. Also, NPY-treated rats which had precocious puberty showed elevated pituitary and plasma LH levels on the day of VO. These results suggest that NPY can activate the hypothalamic-pituitary-gonadal axis to precociously initiate puberty

ISSN:0028-3835    

DOI:10.1159/000126327

出版商:S. Karger AG    

年代:1992

数据来源: Karger

摘要:

Recently, it was demonstrated that intracerebroventricular (icv) injection of interleukin-1 (IL-1) stimulated circulating interleukin-6 (IL-6) to a greater degree than intravenous (iv) injection of IL-1. The goal of this study was to compare the efficacy of lipopolysaccharide (LPS), injected both icv and iv, on circulating concentrations of IL-1 and IL-6. Both iv and icv injection of LPS stimulated plasma levels of IL-1 to a similar degree. However, iv injection of LPS was significantly more efficacious than icv injection of LPS in elevating circulating IL-6. These results demonstrate that like iv injection of LPS, icv injection of LPS stimulates plasma levels of IL-1 and IL-6. Increases in circulating cytokines during infectious diseases which are limited to the central nervous system may serve to activate peripheral functions of an acute phase response.

ISSN:0028-3835    

DOI:10.1159/000126328

出版商:S. Karger AG    

年代:1992

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000126329

出版商:S. Karger AG    

年代:1992

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000126330

出版商:S. Karger AG    

年代:1992

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000126331

出版商:S. Karger AG    

年代:1992

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000126305

出版商:S. Karger AG    

年代:1992

数据来源: Karger