摘要:

We have previously demonstrated that, in the rabbit, both LH and FSH secretions are controlled by shortloop feedback regulatory systems which are highly specific and sensitive. FSH secretion is suppressed by FSH; LH secretion is suppressed by LH and hCG. We have now evaluated the possible role of α- and β-subunits of hCG in the control of LH secretion in rabbits. Experiments were performed in unanesthetized castrated female rabbits bearing chronically implanted silastic catheters to permit repeated blood sampling without anesthesia. Intravenous injections of purified α- and β-chain of hCG were administered in dose levels from 10 to 300 μg, and blood samples were taken from -30 to 240 min before and after the bolus injections. Peripheral levels of rabbit FSH and LH were determined by RIA systems, which do not cross-react with intact hCG or its α- and β-subunits. By analysis of variance, no significant suppression of LH and FSH occurred in response to these doses of the subunits. Intact hCG, in doses of 1 μg, produced a sharp decrease in rabbit LH levels within 10 min. These in vivo studies demonstrate that there is no intrinsic activity of the dissociated purified α- and β-hCG sub-units on the shortloop feedback control of gonadotropins in t

ISSN:0028-3835    

DOI:10.1159/000123241

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

A single injection of the opiate antagonist, naloxone (NAL), resulted in a fourfold increase in serum luteinizing hormone (LH) concentration 20 min after injection. To determine whether noradrenergic neurons were involved, male Sprague-Dawley rats were treated with α-methyl-p-tyrosine (α-MPT), phenoxybenzamine hydrochloride (PBH), or diethyl-dithiocarbamate (DDC), all anti-noradrenergic drugs. Reduction of hypothalamic norepinephrine synthesis by α-MPT or DDC, or blockade of the α-receptors by PBH, resulted in complete suppression of NAL-induced LH release. These results suggest that the NAL-induced increase in LH release is mediated in part via a hypothalamic noradrenergic mechan

ISSN:0028-3835    

DOI:10.1159/000123242

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Serum levels of luteinizing hormone (LH), follicle stimulating hormone (FSH), prolactin, estradiol-17β and testosterone were determined in adult rats that were treated in the neonatal period with monosodium L-glutamate (MSG) which has previously been shown to reliably produce destruction of arcuate nucleus perikarya. MSG-treated males had significantly smaller accessory sexual organs (seminal vesicles and ventral prostate) and testes and had significantly lower serum concentrations of FSH and testosterone than sex-matched controls. MSG-treated females had significantly lower serum concentrations of LH, FSH and estradiol-17β. Prolactin levels in MSG-treated rats were no different than sex-matched controls. This marked reduction in gonadal steroid levels (168%) and inappropriately low gonadotropin levels further characterizes the deficit of feedback regulation in the hypothalamic-pituitary-gonadal axis in MSG-treated rat

ISSN:0028-3835    

DOI:10.1159/000123243

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The effect of the pineal gland on prolactin (PRL) synthesis, storage and release was tested in female rats. To do this, we incubated in vitro hemi-anterior pituitaries from 80-day-old female rats that had been rendered, 8 weeks previously, either blind-anosmic, blind-anosmic and pinealectomized or left intact. Reproductive organ weights, pituitary weights and pituitary DNA content were decreased in animals rendered both blind and anosmic. These effects were reversed by removal of the pineal gland. Additionally, the serum levels of PRL were diminished in blind-anosmic rats from that of intact controls. The synthesis of PRL in vitro was dramatically reduced in the pituitaries of blind-anosmic rats as evidenced by a 63% decrease in [3H]leucine incorporation into PRL from that observed in the intact group. Likewise, the total amount (medium + pituitaries) of radioimmunoassayable PRL in vitro was depressed by 26% in the blind-anosmic group as compared with intact controls. Pinealectomy reversed the reductions in de novo synthesized and total immunoreactive PRL in vitro. From these studies we conclude that in the blind-anosmic female rat the pineal chronically inhibits PRL synthesis and storage in the pituitary and, possibly, its release into the blood. These pineal-induced effects could be accounted for by a reduction in the pituitary mammotroph population as might be indicated by the decrease in pituitary DNA content observed in dual-sensory deprived rats.

ISSN:0028-3835    

DOI:10.1159/000123244

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Variations in serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), prolactin (PRL), growth hormone (GH), and corticosterone in the states of arousal, slow wave sleep and paradoxical sleep were studied as a function of time from the onset of arousal and sleep which were determined polygraphically in 27- to 30-day-old female rats. Markedly high LH values occurred more frequently during slow wave sleep than during other stages, resulting in a tendency to greater mean LH levels in the state of slow wave sleep. Variations in PRL values at various states of the sleep-waking cycle were not very large, but a statistically significant peak occurred shortly after the sleep onset. The mean PRL values obtained after 5 min of paradoxical sleep were lower than those obtained during slow wave sleep. Mean GH values were higher during sleep than arousal state, and the mean during paradoxical sleep was highest. GH levels peaked at 30 min after sleep onset. Corticosterone values were highest in the arousal state, and decreased abruptly after 20 min of sleep. There were no significant variations in FSH and TSH levels in serum during various sleep-waking states. These secretory patterns of anterior pituitary hormones during a sleep-waking cycle are quite similar to those in man.

ISSN:0028-3835    

DOI:10.1159/000123245

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Release of α-MSH from rat hypothalamic slices was characterized with respect to ionic requirements and possible diurnal variations using a sensitive radioimmunoassay. Addition of 47 mM KCl to the superfusion medium resulted in a twofold increase in α-MSH release compared to spontaneous release. Removal of calcium from the superfusion medium abolished the potassium-evoked release of α-MSH. This supports the concept that α-MSH functions as a neurotransmitter or neuromodulator in the hypothalamus. Both spontaneous and potassium-induced α-MSH release were related to diurnal variation. Marked release from the slices was observed at 10.10 h, corresponding to a peak in the α-MSH concentration in the hypothalamus [18] and to a low level of α-MSH in the blood. Contrarily, no significant release from the hypothalamus was obtained at 17.00 h when hypothalamic α-MSH content was low, but blood levels exhibited a peak. These findings suggest that there are differences in the regulation of the α-MSH from the pituitary and that in the hypo

ISSN:0028-3835    

DOI:10.1159/000123246

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

In order to characterize plasma prolactin (Prl) patterns during the estrous cycle and pseudopregnancy (PSP), I collected sequential blood samples between 8.00 and 19.00 h at 1-hour, 1.5-min or 1-min intervals from conscious, unrestrained female rats. During the afternoon of proestrus and estrus a single Prl surge was observed, while during PSP two daily Prl surges occurred, one nocturnal and one diurnal. During PSP the secretion of Prl occurred occasionally in substantial bursts from baseline levels. This contrasted with the proestrus afternoon surge when plasma Prl levels were constantly elevated due to a more or less continuous release of fluctuating amounts of Prl. The differences in timing and secretion patterns of the three surges suggest a separate neural regulation. The diurnal surge on day 0 of PSP may be composed of two different surges which also may have a separate neural regulation: one peak occurs at 14.00–16.00 h, and is comparable in timing to the Prl surge during the afternoon of estrus; a second surge starts at 17.00 h, and is comparable in time of onset to the diurnal surge on the other days of PSP. Plasma Prl always appeared to increase in an unpredictable manner, discontinuously by means of several bursts, with maximum increments of about 600 ng/ml/min. The shortest half-time values, as calculated from the disappearance of Prl from the circulation, were about 2.2 min. The individual patterns show that Prl release must be the consequence of a very dynamic neural regulatory proces

ISSN:0028-3835    

DOI:10.1159/000123247

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

Single rat neurohypophyses were impaled on a platinum electrode, perifused with isotonic medium and fractions of perifusate collected each minute. Arginine vasopressin content of the fractions was measured by radioimmunoassay. The basal release of arginine vasopressin varied from 50 to 350 pg (0.02–0.14 mU/min) between individual neurohypophyses. Recordings previously obtained from rat supraoptic neurones provided the patterns for electrical stimulation. 8-min segments of a phasically and a continuously firing neurone were selected such that each was firing at a mean rate of 6 spikes/s and possessed very similar overall distributions of interspike intervals. In 15 experiments individual neurohypophyses were stimulated with the phasic pattern, followed by the continuous pattern, or vice versa, separated by an 8-min unstimulated period. In either case, significantly more hormone was released during phasic stimulation than during continuous stimulation. It is concluded that the phasic firing pattern typical of vasopressin neurones is highly efficient for the release of vasopressin from the neurohypophysis, but that its effectiveness does not lie in an increased preponderance of short interspike interval

ISSN:0028-3835    

DOI:10.1159/000123248

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

The effect on plasma prolactin (PRL) of two indirectly acting DA agonists (IADA), i.e., methylphenidate and amineptine was studied in normo- and hyperprolactinemic subjects. PRL responses to methylphenidate and amineptine were compared to those previously obtained with the use of another IADA, namely, nomifensine. In normoprolactinemic women methylphenidate (20 mg, orally) or amineptine (200 mg, orally) induced a significant decrease in baseline PRL (maximal change from baseline 50% at 90 min), a pattern reminiscent of that induced by nomifensine (maximal change from baseline 35% at 120 min). Likewise, in puerperal women (postpartum day 2) methylphenidate and amineptine induced a clear-cut lowering of baseline PRL (40% inhibition at 90 min and 180 min, respectively); nomifensine induced 60% inhibition of resting PRL levels at 150 min. In subjects with pathological hyperprolactinemia (proven or highly probable PRL-secreting tumor or uncertain etiology), previously shown to be unresponsive to the PRL-lowering effect of nomifensine, methylphenidate or amineptine did not significantly lower baseline PRL (maximal change from baseline 8% at 150 min and 3% at 90 min, respectively). In few of these subjects methylphenidate and amineptine failed to lower plasma PRL levels also at doses of 30 and 300 mg, orally, respectively. These data indicate that (1) two other IADA, i.e., methylphenidate and amineptine, are effective PRL-lowering agents in both normoprolactinemic and puerperal subjects, whereas they are unable to lower plasma PRL in patients with proven or probable PRL-secreting tumors; (2) the ability of the different drugs to inhibit plasma PRL in puerperal versus pathological hyperprolactinemia emphasizes the different tuberoinfundibular DA (TIDA) neurotransmission present in the two clinical conditions; (3) in view of the mechanism of action of the IADA, there is a defect in TIDA metabolism or transport in patients harboring a prolactinoma.

ISSN:0028-3835    

DOI:10.1159/000123249

出版商:S. Karger AG    

年代:1981

数据来源: Karger

摘要:

This study was aimed at determining the α-MSH and ACTH contents of the neurointermediate lobe (NIL) of the mouse hypophysis during ontogenesis, as well as the ability of the gland, incubated in a perfusion system, to respond to dopamine (DA) and high potassium (K+). We showed that: (1) the NIL content of α-MSH exhibited a biphasic pattern of evolution, characterized by a dramatic increase appearing between postnatal days 3 and 5. By contrast, NIL ACTH content followed a completely different pattern of evolution; (2) both DA and high K+ reversibly inhibited MSH release from superfused NIL, the latter effect being more pronounced with the use of pituitaries from 7-day-old than from 1-day-old mice; (3) the inhibitory influence of high K+ was impaired by haloperidol pretreatment. From these data, as well as from morphological observations, it appears that functional DA receptors seem to be present on melanotrophs of the developing hypophysis in mice and that the increase in α-MSH in IL cells observed shortly after birth may result from the onset of inhibitory influence exerted by dopaminergic innervation on hormonal secretion. This view, however, does not preclude possible effects of other hypothalamic releasing and/or inhibiting facto

ISSN:0028-3835    

DOI:10.1159/000123250

出版商:S. Karger AG    

年代:1981

数据来源: Karger