摘要:

This study examined the possible involvement of dopamine (DA) and/or serotonin (5-HT) in regulating basal pulsatile LH release, and in mediating perisuprachiasmatic (peri-SCN)-induced suppression of pulsatile LH secretion in ovariectomized rats. Unanesthetized animals were bled continuously through jugular vein cannulae for a 1½-h prestimulation period, 1½ h of stimulation, and up to 3/4 h after stimulation. Control rats were untreated or given d-butaclamol, the inactive stereoisomer of d-butaclamol. Other groups were pretreated either with pimozide or d-butaclamol to block DA receptors, parachlorophenylalanine (PCPA) or metergoline to inhibit 5-HT synthesis or block 5-HT receptors, respectively, or PCPA + pimozide to affect both 5-HT and DA systems. Prior to stimulation, regardless of whether DA and/or 5-HT systems were interfered with, no significant differences existed in mean blood LH levels, LH interpulse intervals, or the magnitude or rate of increase in blood LH levels for individual LH episodes. This suggests that DA and/or 5-HT may not be essential parts of the neurotransmitter systems regulating basal pulsatile LH secretion. During peri-SCN stimulation significant decreases in mean blood LH levels occurred in all groups. This was due entirely to a lengthening in the interval between LH pulses, since no group showed a decrease in the magnitude or rate of increase in blood LH levels for those LH pulses that did occur during stimulation. These results indicate that peri-SCN-induced suppression of pulsatile LH release is not mediated by known DA and/or 5-HT neuronal inputs to this region, and suggest that the peri-SCN area may be one brain region that influences, in a suppressive manner, only the periodicity of the pulsatile LH release process in the ra

ISSN:0028-3835    

DOI:10.1159/000123068

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Regeneration of rat adrenals was studied after bilateral enucleation to determine whether there is a neural component mediating this process as there is in compensatory adrenal growth after unilateral adrenalectomy. Regeneration was approximately 50% complete (based on criteria of wet weight and DNA content) by 10 days after enucleation; at this time circulating ACTH levels were twice as high in enucleates as in sham-operated controls, but corticosterone levels were normal. Regeneration was apparently complete at sometime between 3 and 6 weeks and circulating ACTH and corticosterone levels were normal at these times compared to controls. Unilateral adrenal enucleation resulted in compensatory growth of the opposite gland, not regeneration of the enucleated gland. Unilateral hypothalamic hemi-islands made with a Halász knife resulted in bilateral augmentation of adrenal regeneration at 10 days and 6 weeks. From these results we conclude that adrenal regeneration after bilateral enucleation occurs by different afferent and efferent mechanisms than compensatory adrenal growth after unilateral adrenalectomy. Additional studies were performed in rats 3 and 6 weeks after adrenal enucleation to test whether the adrenal medulla participates either in compensatory adrenal growth or in the augmented ACTH response to ether vapors observed in unilaterally adrenalectomized rats. Normal compensatory adrenal growth occurred 3 days after unilateral adrenalectomy in rats bilaterally enucleated 6 weeks earlier. Prior enucleation did not inhibit the increased ACTH response of unilaterally adrenalectomized rats to ether. Therefore, the adrenal medulla does not mediate compensatory adrenal growth or the augmented ACTH response of unilaterally adrenalectomized rats to ACTH-releasing stimuli

ISSN:0028-3835    

DOI:10.1159/000123069

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The present study was undertaken to determine the effects of androgen implants in the preoptic area-suprachiasmatic nucleus (POA-SCN) on catecholamine turnover in the POA-SCN and the medial basal hypothalamus (MBH) in orchidectomized rats. Bilateral implants of testosterone (T) or dihydrotestosterone (DHT) in the POA-SCN of orchidectomized rats did not affect serum concentrations of LH and FSH or the turnover of dopamine (DA) and norepinephrine (NE) in the MBH. In the area surrounding the implants in the POA-SCN, T and DHT decreased dopamine turnover by 67 and 37%, respectively, without influencing the POA-SCN norepinephrine turnover. These results indicate (i) that T implants in the POA-SCN selectively depress POA-SCN dopamine turnover, (ii) that this effect of T may occur following its conversion to DHT, and (iii) that these androgen effects probably do not mediate the negative feedback action of T on gonadotropin secretion.

ISSN:0028-3835    

DOI:10.1159/000123070

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Angiotensin II (AII) was infused into the lateral cerebral ventricle of rats given water, isotonic saline, or hypertonic saline ad libitum, or 40 ml water/day. Fluid intake, change in body weight, plasma [Na+], and plasma and pituitary arginine vasopressin (AVP) levels were measured. Isotonic saline or All (1 µg/µl saline) was infused at 1 µl/h for 5 days using osmotic minipumps. All increased fluid intake of rats given isotonic saline to drink; they consumed an average of 269 ± 25 ml/day on day 5. All infusions in rats given water or isotonic saline to drink decreased plasma [Na+] with no changes in plasma or pituitary AVP. However, in rats given hypertonic saline, plasma [Na+] remained at control levels while plasma AVP increased. In water-restricted rats, the effects of AII were intermediate: a small decrease in plasma [Na+] and a small increase in plasma AVP. From these results, it is suggested that although acute All administration elicits AVP release, this effect diminishes during chronic ATI infusion, coincident with reduced plasma [Na+

ISSN:0028-3835    

DOI:10.1159/000123071

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Compared to heterozygous Brattleboro animals, homozygous (diabetes insipidus) rats exhibited higher steady-state levels of serotonin in the mesencephalon, septum and striatum. These differences disappeared upon the administration of pargyline, suggesting a decreased accumulation of serotonin. The norepinephrine level was higher in the mesencephalon, while the disappearance rate (α-methyl-p-tyrosine) was accelerated in the septum and decreased in the hypothalamus. The lower striatal dopamine level was associated with a decreased disappearance rate. The data suggest that the altered monoamine metabolism might be associated with the known endocrine and behavioral disturbances of the homozygous rats

ISSN:0028-3835    

DOI:10.1159/000123072

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

We attempted to determine whether release of endogenous somatostatin (SS) in rats might mediate the apparent inhibition of growth hormone (GH) secretion produced by metergoline or yohimbine injection. Plasma GH levels in adult male rats bearing chronic right-atrial cannulae were measured at 15-min intervals during a 4-hour period around the onset of the daily dark period. Plasma GH levels in control rats (vehicle-injected) rose rapidly from low levels (300 ng/ml) around the onset of the dark period, then declined to low values within 2 h. Injection of the serotonin receptor antagonist metergoline (5 mg/kg) or the adrenergic blocker yohimbine (10 mg/kg) 2.25 h before darkness significantly suppressed the subsequent rise in plasma GH levels. The effect of metergoline, but not yohimbine, on plasma GH was markedly reversed when animals were injected intravenously with anti-SS serum (0.5 ml) 1 h after drug administration. These data suggest that circulating SS may mediate the GH inhibition produced by injection of a serotonin receptor blocker; however, other factors are apparently involved in the suppression of GH secretion by yohimbine.

ISSN:0028-3835    

DOI:10.1159/000123073

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

VIP stimulated prolactin secretion from incubated rat hemipituitaries. Under the same conditions, the secretion of GH, LH, FSH was not affected. The stimulation of prolactin was dose-dependent, with an apparent affinity of VIP of 10.9 ± 3.1 nM and a maximal stimulation of 57.7 ± 4.2%. Secretin, a structurally related peptide, was also active at higher concentrations whereas another partial analogue, glucagon, was ineffective. The effect of VIP was not blocked by α-flupentixol, a potent dopaminergic antagonist, at concentrations which antagonized the dopamine inhibition of prolactin secretion. Stimulation by VIP and TRH was additive. Neither Metenkephalin nor naloxone interfered with the response to VIP. It thus seems that specific VIP receptors are present on pituitary prolactin cells. VIP, present in the mediobasal hypothalamus and detected in the hypothalamo-hypophyseal portal blood therefore is a good candidate as a physiological P

ISSN:0028-3835    

DOI:10.1159/000123074

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Exposure to short day lengths for 9 weeks renders the hypothalamic-pituitary axis of the castrate hamster extremely responsive to the negative feedback effect of exogenous testosterone. The systemic and/or local conversion of testosterone to 5α-dihydrotestosterone (5α-DHT) or 17β-estradiol (E2) is considered to be an important step in its action on target tissues. The present study was designed to determine if the photoperiod can induce changes in the sensitivity of the hypothalamic-pituitary axis to the inhibitory effects of 5α-DHT or E2. 5α-DHT-filled Silastic capsules that were 2, 4, or 8 mm long greatly reduced serum LH and FSH levels in castrates that were exposed to a nonstimulatory LD 8:16 light cycle, but not in animals exposed to a stimulatory LD 14:10 light cycle. E2 capsules that were 1, 2, 4, or 8 mm long greatly reduced serum LH and FSH levels in castrates exposed to LD 8:16, but not in animals exposed to LD 14:10. Serum gonadotropin levels were reduced in all of the animals receiving the larger 5α-DHT (20 or 50 mm long) or E2 (20 mm long) capsules, irrespective of photoperiod. Thus, the photoperiod can alter the sensitivity of the gonadotropin control center to the negative feedback effect of both the 5α-reduced derivative of testosterone, 5α-DHT, and the aromatized metabolite of testosterone, E2. These results suggest that testicular secretions besides testosterone and/or extratesticular conversion of testosterone to its metabolites may be involved in the photoperiodic inhibition of the hamster reproductive

ISSN:0028-3835    

DOI:10.1159/000123075

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

The influence of the anterior pituitary on tissue CRF was investigated in two sets of experiments using lesioned, hypophysectomized, adrenalectomized donor rats. Donors were injected with 1 or 0.5 anterior pituitary equivalents 3 h before transfer of plasma to recipient animals. Injection of 1 pituitary equivalent significantly reduced levels of corticosterone in recipient rats compared to saline injection at 3 different time intervals following the transfer. In a second series of experiments donor animals received replacement with saline, ACTH, TSH, or PRL at 0, 2 and 4 h following adrenalectomy; transfer of plasma to recipient animals was at 5 h. Of the three hormones injected only ACTH significantly reduced tissue CRF activity in donor animals. Recipients of these donors showed suppressed levels of corticosterone compared to recipient animals whose donors were injected with saline, TSH or PRL. The ACTH dose-response curve indicates that the effective dose for suppression of tissue CRF in donor animals is in the range of 1–10 mU/ml. Results of these experiments clearly show that tissue CRF is inhibited by the anterior pituitary hormone ACTH rather than by elevated levels of corticosterone. These experiments suggest that feedback regulation of tissue CRF release by ACTH may occur in response to prolonged physical stres

ISSN:0028-3835    

DOI:10.1159/000123076

出版商:S. Karger AG    

年代:1980

数据来源: Karger

摘要:

Two anterior pituitary homografts were inserted under the left kidney capsule of adult male Sprague-Dawley rats (experimental rats). Sham-treated rats were exposed to identical surgical manipulations, but no tissue was inserted under the kidney capsule. The concentrations of dopamine (DA) and noradrenaline (NA) were determined in the median eminence, intermedioposterior pituitary and telencephalon by a radioisotope-enzyme technique. The decline in DA or NA 2 h after treatment with α-methyl-β-tyrosine provided a measure of DA and NA turnover, respectively. A marked increase in DA turnover was observed in the median eminence of the experimental compared to the sham-treated rats at 1, 3 and 6 days following surgery. The concentrations of DA and of NA were significantly reduced in the median eminence of the experimental rats compared to sham-treated rats at both 3 and 6 days following surgery. No statistically significant increases in DA or NA turnover were observed in either the intermedioposterior lobe of the pituitary or the telencephalon of the experimental animals compared to sham-treated animals at any time investigated. Serum prolactin (PRL) levels were significantly elevated in the experimental animals compared to the sham-treated animals by 3 days following surgery. The results of these studies clearly show that the turnover of DA in the terminals of the tuberoinfundibular neurons is increased by 1 day following the transplantation of anterior pituitary homografts under the kidney capsule. Future studies will be required to determine if this response is due exclusively to an early increase in serum PRL level

ISSN:0028-3835    

DOI:10.1159/000123077

出版商:S. Karger AG    

年代:1980

数据来源: Karger