摘要:

Somatomedin C (SMC; insulin-like growth factor I) is thought to mediate the effects of growth hormone (GH) mainly on skeletal growth. SMC is produced in the liver but its production by various other fetal tissues including the brain, suggests a local regulatory role rather than a general one. A substance cross-reacting with recombinant human SMC (rSMC) was localized in the central nervous system (CNS) of the normal control and Snell dwarf mice by the unlabeled antibody peroxidase-antiperoxidase technique. rSMC-immunoreactive substance (rSMC-IRS) was found in the neuronal cells of forebrain structures. These included the caudate nucleus/putamen, hippocampus, thalamus, hypothalamus, globus pallidus and amygdala. No positive cells were found in the cerebral cortex. Investigation of the dwarf brain showed rSMC-IRS distributed in identical areas of the brain, although the intensity of the staining of rSMC-IRS was found to be weaker than that of the positive cells in the normal brain. Moreover, the number of positive cells was found to be less than in the normal brain. After treatment with bovine GH for 3 days the reduced number of positive cells and weaker staining in the cerebral sections of the dwarf mice did not change. Thus, rSMC may represent another peptide which is common to both the endocrine and the nervous system, with a potential neurotransmitter/neuromodulator function in the CNS.

ISSN:0028-3835    

DOI:10.1159/000124833

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The studies reported in this paper were undertaken to investigate the effect of chronic (10 day) alcohol consumption on female pituitary-gonadal function. The immature female rat model treated with pregnant mare serum gonadotropin (PMSG) was used since it results in a highly reproducible luteinizing hormone (LH) surge and ovulation. Twenty-day-old female rats were placed on diets that were either (1) unrestricted (ad libitum); (2) contained 5% ethanol in a liquid diet, or (3) isocalorically pair-fed with the liquid diet to the ethanol group. After 10 days on their respective diets, the groups were subdivided and given either 8 IU of PMSG in 0.1 ml saline or 0.1 ml saline s.c. between 10.00 and 11.00 h. The animals were sacrificed by decapitation at 24, 48, 52, 54, 56, 58, 60 and 62 h after injection. Trunk blood was obtained for serum measurements of LH. The uteri were weighed and prepared for the histological study. In all dietary groups, serum LH levels were significantly higher in the PMSG-treated animals when compared to the saline controls at all time intervals with the exception of the alcohol 58-hour group. In the ad libitum animals, plasma LH concentrations were highest at 52 h following hormone administration. The serum LH concentrations were highest at 56 h after hormone administration in the pair-fed group and were significantly less than the ad libitum group at 52, 54, 56, and 58 h after PMSG stimulation. No significant plasma LH surge was observed in the alcohol group and the LH concentrations were significantly less than the pair-fed rats at 56 and 58 h after PMSG treatment. In contrast to the alterations in LH levels, the PMSG-induced increase in uterine weights and histological evidence of estrogenization were not as dramatically changed by any of the dietary modifications. Thus, chronic alcohol consumption appears to have a greater effect on pituitary gonadotropin secretion than on the gonadal aspects of reproductive function. These studies further suggest that caloric restriction in both the alcohol and pair-fed animals significantly decreased PMSG-induced LH release. Nonetheless, chronic alcohol consumption causes an additional impairment which may be manifest throughout the hypothalamic-pituitary-gonadal axis.

ISSN:0028-3835    

DOI:10.1159/000124834

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The N-terminal acetylation of melanophore-stimulating hormone (MSH) increases the melanotropic potency of the peptide. This modification may be important in amphibians, where MSH causes skin darkening during adaptation to black background. This study examines the acetylation status of the peptide in the toad Xenopus laevis under different conditions of background adaptation. Acetylated and nonacetylated α-MSH were analyzed by high-performance liquid chromatography and quantified by radioimmunoassay. The acetylation status of α-MSH was analyzed in tissue, in plasma and in media obtained from in vitro incubation of neurointermediate lobe tissue. Nonacetylated MSH is the major form of α-MSH in tissue from both black- and white-background-adapted animals. In plasma of black-adapted animals only acetylated α-MSH could be detected. Plasma MSH levels of white-adapted animals were barely detectable. Analysis of peptides secreted during in vitro incubations of neurointermediate lobe tissue from black-adapted animals showed that the relative contribution of α-MSH to the immunoreactive profile was considerably enhanced, which supports the concept that acetylation of MSH in Xenopus is associated with the secretory process. Acetylation capacity of tissue from white-adapted animals was much lower and only after several days on black background was full capacity acquired. It is suggested that de novo biosynthesis of acetylation enzymes may be necessary for the acquisition of the acetylation capacity. Transfer of black animals to white background caused a rapid decrease in acetylation capacity, which suggests that factors involved in the rapid inhibition of secretion might also regulate acetylation. This finds support in the observation that dopamine was effective in partially inhibiting the acetylation capacity of this tissue. It is concluded that the acetylation of MSH in the pars intermedia of X. laevis is a regulated process related to physiological parameters concerning background c

ISSN:0028-3835    

DOI:10.1159/000124835

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The effects of castration and testosterone (T) replacement on levels of substance P (SP) and luteinizing hormone-releasing hormone (LHRH) were assessed in discrete areas of the male hamster brain. The animals were either castrated, castrated and given a chronically low or high dose of T by Silastic implant, or sham-operated. Brain tissues and trunk blood were collected 3 weeks after surgery. Plasma T levels were maintained within the normal range by the implants but at significantly lower or higher levels than the mean for sham-operated males. Levels of SP and LHRH were quantified in the olfactory bulbs, rostral basal forebrain, anterior hypothalamic and preoptic area, medial basal hypothalamic area and median eminence, and brain stem. In general, castration and T replacement effected opposite changes in levels of SP and LHRH. In the medial basal hypothalamic area and median eminence SP levels were found to be inversely related to the chronic T levels, whereas the LHRH levels were directly correlated. In the anterior hypothalamic and preoptic area, castration reduced levels of SP. Conversely, castration elevated levels of LHRH in this area. This inverse dynamic relationship between changing peptide levels was also observed in the rostral basal forebrain but not in the olfactory bulbs. In most of these forebrain regions, the dose-response curves for the experimental groups could not incorporate the peptide levels in the sham-operated control group. SP levels in the brain stem showed a monotonic inverse relationship to circulating T levels which did include the control group values. The results are consistent with hypotheses that LHRH expression and release in the basal forebrain and diencephalon may be partially regulated by SP-containing neuronal systems, and that variations in circulating T levels associated with episodic gonadotropin secretion are important for maintaining normal LHRH and SP levels in the forebrain.

ISSN:0028-3835    

DOI:10.1159/000124836

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The effects of acetylcholine and of the muscarinic receptor agonist carbachol on inositol phosphate production were studied in cultured rat anterior pituitary cells. In the presence of the cholinesterase inhibitor physostigmine, acetylcholine significantly (p < 0.05–p < 0.01) stimulated inositol phosphate formation in a concentration-related fashion; carbachol, but not oxotremorine, produced similar effects. The increase in the amount of inositol phosphates (primarily inositol trisphosphate and inositol bisphosphate) was very rapid, an effect potently antagonized by the muscarinic receptor antagonist atropine. This agent significantly attenuated the stimulatory effect of carbachol on growth hormone (GH) release. These results indicate that the effects exerted by acetylcholine on anterior pituitary function (i.e. GH release) may be mediated, at least in part, by receptor-activated polyphosphoinositide hydrolysis. In addition, acetylcholine and car-bachol’s relation with other intracellular pathways and with hormone release is discus

ISSN:0028-3835    

DOI:10.1159/000124837

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Regulation of the pituitary-thyroid axis in rats with hypothalamic knife cuts has been studied. Complete hypothalamic deafferentation, either limited to the median eminence and the arcuate nucleus, or including parts of the dorsomedial nucleus and the whole ventromedial nucleus caused an increase in thyrotopin (TSH)-releasing hormone (TRH)-induced TSH secretion. Using an immunocytochemical procedure, a few TRH-positive fibers were observed within the median eminence of the larger island, while almost no fibers were identified in the smaller island. The exaggerated TSH response to TRH appeared within 3 days after the surgery and lasted for at least 1 week, when blood thyroxine (T4) level was significantly lowered. Exogenously injected T4 could inhibit such responses of TSH in the deafferented rats in a dose-related manner. These results support the hypothesis that the increase in the TSH response to TRH following hypothalamic deafferentation is due, at least in part, to the lowered thyroid hormone level in the blood.

ISSN:0028-3835    

DOI:10.1159/000124838

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Previous studies have shown that prepubertal olfactory bulbectomy will prevent the testicular regression associated with short photoperiod in golden hamsters. The gonadal regression which normally occurs in hamsters on short photoperiod is known to be due in part to an increased responsiveness of the reproductive neuroendocrine system to the negative feedback actions of testosterone on LH and FSH secretion. The present study tested whether the olfactory bulbs influence the feedback effects of testosterone on gonadotropin secretion. Twenty-four- to 26-day-old male golden hamsters were either olfactory-bulbectomized (BX) or sham-olfactory-bulbectomized. Eight weeks later, all hamsters were castrated, and one half of each group was placed in LD 10:14 (this was called week -8 of the study), while the other half was returned to long photoperiod (LD 14:10). Eight weeks following castration (week 0 of the study), all animals were implanted with silastic capsules containing 0, 4, 8 or 16 mm of testosterone. All hamsters were bled by cardiac puncture at -8, -4, 0, +2, +4, +6 and + 8 weeks. The concentration of LH and FSH in these samples was then determined by RIA. BX completely prevented the negative feedback of testosterone on gonadotropin secretion in hamsters on either long or short photoperiod at all levels of testosterone tested in this study. In addition, there were seemingly steroid-independent effects of BX on gonadotropin levels in the castrated hamsters prior to testosterone replacement at weeks -4 and 0. These results are the first indication that the olfactory bulbs have an important role in regulating the responsiveness of the reproductive neuroendocrine axis to the feedback of testosterone on LH and FSH secretion. The data indicate that the ability of BX to prevent short-photoperiod-induced testicular regression may be one part of a much larger effect of the olfactory bulbs, and that the olfactory bulbs have an important influence on gonadotropin secretion in hamsters maintained on long or short photoperiod.

ISSN:0028-3835    

DOI:10.1159/000124839

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Selectively bred long-sleep (LS) and short-sleep (SS) mice differ markedly in ethanol-induced adrenocortical response. Intracerebroventricular injections of saline elicited a ‘stress-induced’ adrenocortical response in both lines of mice, and intracerebroventricular infusions of noradrenergic and cholinergic compounds modulated ethanol-induced and stress-induced adrenocortical responses differentially in these mice. Clonidine, an α2-adrenergic agonist, blocked ethanol-induced elevations in plasma corticosterone in a dose-dependent manner (1 and 10 µg) in LS mice; however, only the 10-µg dose of clonidine effectively antagonized this response in SS mice. Clonidine was less effective in blocking adrenocortical activity induced by stress than that induced by ethanol. Yohimbine, an α2-adrenergic antagonist, induced a marked elevation in plasma corticosterone in LS mice but not in SS mice; however, this compound did not alter ethanol-induced adrenocortical responses in either line of mice. Yohimbine reversed the inhibitory effect of clonidine in ethanol-treated LS and SS mice. Phentolamine, a nonspecific α-adrenergic antagonist, and propranolol, a β-adrenergic antagonist at high doses (10 µg), produced slight increases in plasma corticosterone in LS mice only. Neither these compounds nor methoxamine, a nonspecific α-adrenergic agonist, altered the effect of ethanol on adrenocortical activity in LS or SS mice. Carbachol, a mixed muscarinic/nicotinic agonist, significantly increased adrenocortical response in both LS and SS mice and potentiated ethanol-induced elevation in plasma corticosterone in both lines of mice. However, atropine, a nonspecific muscarinic antagonist, or hexamethonium, a nicotinic antagonist, did not modify ethanol-induced elevations in plasma corticosterone in LS and SS mice. These results suggest that adrenocortical activation produced by ethanol may be mediated primarily through central noradrenergic systems and that differences in these systems may account for the differential ethanol-induced elevation in plasma corticosterone exhibited by LS

ISSN:0028-3835    

DOI:10.1159/000124840

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

The use of intercavernous sinus phlebography for the diagnosis and neurosurgical treatment of pituitary adenomas has enabled the collection of selective venous samplings of the inferior petrosal sinuses (IPSs), where prolactin (PRL) levels can be measured before the hormone becomes excessively diluted in the systemic circulation. In the present study, plasma PRL levels were studied in the right and/or left IPS and, simultaneously, in the peripheral circulation of: (1) normoprolactinemic patients affected with various pituitary disorders which required phlebographic procedures; (2) hyperprolactinemic patients with negative radiological and computed tomographic(CT) signs of pituitary adenomas and (3) adenomatous hyperprolactinemic patients. In the 17 normoprolactinemic patients, the plasma PRL concentration in the IPSs was significantly higher (3.5 times; p < 0.01) than in the peripheral circulation. In the 11 hyperprolactinemic patients with negative radiological and CT signs of pituitary adenomas, the central gradient for PRL was significantly higher (2.8 times; p < 0.05) than in the peripheral circulation. No significant difference was detected between PRL concentrations in the left and right IPSs. In the 11 adenomatous hyperprolactinemic patients, there was a significant (p < 0.01) central gradient for PRL 3.8 times higher than in the peripheral circulation on the ipsilateral side of the tumor. Furthermore, the plasma PRL concentration in the ipsilateral IPS was significantly higher (3.4 times; p < 0.05) than that in the contralateral sinus. In conclusion, the present study shows that a clear-cut concentration gradient exists between plasma PRL levels in the IPSs and in the peripheral circulation of normoprolactinemic and hyperprolactinemic patients with negative radiological and CT signs of pituitary adenomas. This gradient was also observed in adenomatous patients when blood was drawn from the ipsilateral IPS. Therefore, this finding demonstrated that in PRL-secreting adenomas there is a lateral gradient of PRL levels coinciding with the tumor side.

ISSN:0028-3835    

DOI:10.1159/000124841

出版商:S. Karger AG    

年代:1987

数据来源: Karger

摘要:

Female hamsters received horizontal knife cuts to investigate the role of hypothalamic connections in the photoperiodic control of female reproductive functions. Knife cuts placed ventral to or through the paraventricular nucleus (PVN), but dorsal to the suprachiasmatic nucleus (SCN), prevented photoperiod-induced acyclicity and uterine regression in animals maintained under a nonstimulatory photoperiod for 10 weeks. The animals were then ovariectomized and tested for lordosis behavior following subcutaneous injections of ovarian hormones to investigate the photoperiodic modulation of female sexual behavior. Animals exposed to a nonstimulatory photoperiod were less behaviorally sensitive to treatment with estradiol benzoate (EB) alone, but did not differ from animals maintained under a stimulatory photoperiod when EB was combined with progesterone. The effect of photoperiod on behavioral sensitivity to hormone replacement was independent of the surgical condition. The results are consistent with the hypothesis that dorsal projections from the SCN to the PVN mediate gonadal responses to short photoperiods. They also indicate that photoperiod-induced changes in behavioral sensitivity to gonadal steroids may be mediated by neural pathways distinct from those that mediate the gonadal changes.

ISSN:0028-3835    

DOI:10.1159/000124842

出版商:S. Karger AG    

年代:1987

数据来源: Karger