摘要:

An increase in endogenous opiatergic tone has been suggested as a mechanism for suppression of gonadotropin release in hyperprolactinemia (hyperPRL). In an attempt to evaluate this possibility in hyperprolactinemic males, we have examined the effects of a specific opiate antagonist, naloxone, on plasma LH levels in adult male rats rendered hyperprolactinemic by transplanting two pituitary glands underneath the kidney capsule. Naloxone was adminstered intravenously (i.v.) at different dose levels (0.2, 2, or 20 mg/kg body weight) and blood samples were collected at intervals ranging from 15 to 60 min after naloxone administration. In all experiments, plasma LH levels in the sham-operated controls were significantly increased after naloxone administration, while those in the pituitary-grafted group remained unaltered. Injecting naloxone daily for 3 or for 10 days failed to alter plasma LH levels in both sham-operated and pituitary-grafted animals. Administration of LHRH induced a 7-fold increase in plasma LH levels in both the pituitary-grafted animals and the sham-operated controls. These studies demonstrate that hyperPRL interferes with the naloxone-induced rise in circulating LH levels in the male rat.

ISSN:0028-3835    

DOI:10.1159/000124145

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The effect of N-(6-aminohexyl)-5-chloro-naphthalene-l-sulfomide (W-7) and trifluoperazine (TFP) was examined on ACTH release from cultured rat anterior pituitary cells and pituitary halves. These drugs significantly inhibited the ACTH release induced by synthetic ovine corticotropin-releasing factor (CRF) in a dose-related manner. In pituitary halves, arginine vasopressin (AVP) at 10 and 100 ng/ml showed almost the same ACTH-releasing activity as CRF at the same concentrations. W-7 and TFP inhibited the CRF- and AVP-induced ACTH release from pituitary halves. The cyclic AMP levels in the pituitary halves were significantly increased by CRF, but not AVP. Although W-7 inhibited CRF-in-duced ACTH release, it did not have an effect in cyclic AMP accumulation. These results suggest that CRF exerts ACTH-releasing activity through both the calcium-calmodulin system and cyclic AMP system and that AVP stimulates ACTH release mainly through the calcium-calmodulin system.

ISSN:0028-3835    

DOI:10.1159/000124146

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

Passive immunization of rats with an antiserum raised against rat growth hormone-releasing factor (GRF) completely inhibited the growth hormone (GH) response to morphine and β-endorphin but did not alter the prolactin (PRL) response to those two stimuli. These results demonstrate that opiate and opioid peptide stimulation of pituitary GH secretion is mediated through hypothalamic GRF and presents an animal model in which the stimulated secretion of GH and PRL can be specifically dissociated

ISSN:0028-3835    

DOI:10.1159/000124147

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The role of ascending noradrenergic projections of medullary origin in regulating the activity of tuberoinfundibular neurons of the hypothalamic paraventricular nucleus (PVN) was examined in pentobarbital-anesthetized male Sprague-Dawley rats. Discrete electrical stimulation of either the Al or the A2 noradrenaline cell group areas of the caudal medulla enhanced the probability of firing in a substantial proportion of antidromically identified tuberoinfundibular PVN cells tested. Notably, no inhibitory effects were observed. Destruction of the PVN noradrenergic terminal plexus by local application of the neurotoxin 6-hydroxydopamine 1 day prior to electrophysiological experiments abolished the effects of both Al and A2 stimulation. These findings indicate that noradrenergic afferents can exert a facilitatory influence on the activity of a population of tuberoinfundibular PVN neurons, thus supporting earlier suggestions that central noradrenergic structures can enhance the release of certain anterior pituitary hormones.

ISSN:0028-3835    

DOI:10.1159/000124148

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

Immunoreactive thyroid-stimulating hormone (IR-TSH) has been detected in the hypothalamus and is released in vitro by a calcium-dependent mechanism when the tissue is depolarized. Recently, immunocytochemical studies have revealed that IR-TSH is present in thyrotropes in the pars tuberalis. Therefore, because these thyrotropes are associated with the median eminence, the area with the highest concentration of IR-TSH, it is of interest to determine if ‘hypothalamic’ IR-TSH is from neural or pituitary cells. We addressed this issue by studying the effects of hypophysectomy, thyroidectomy, or chronic administration of triiodothyronine (T3) or thyroxine (T4) on the distribution and in vitro release of IR-TSH in the hypothalamus. We reasoned that, if hypothalamic IR-TSH is dependent on the thyrotropes of the pars tuberalis, then changes in hypothalamic IR-TSH concentration and release should be parallel to those measured in pituitary extracts. IR-TSH was measured in tissue extracted in ice-cold 2% NaCl, with a final pH of 4.5. For the in vitro studies, tissues were incubated for 20-min periods in Krebs-Ringer bicarbonate buffer at 37 °C. In untreated rats, the concentration of IR-TSH is greater in the ventral than the dorsal portion of the hypothalamus (39.3 ± 8.2 vs. 4.0 ± 1.5 ng/mg wet wt). Upon finer dissection of the hypothalamus into median eminence and anterior, middle, and posterior portions of the remainder, IR-TSH was only detectable in the middle hypothalamus (5.3 ± 1.5 ng/mg), and the median eminence (149 ± 41 ng/mg). After thyroidectomy, pituitary IR-TSH content and the spontaneous in vitro release decreased, while the hypothalamic IR-TSH concentration and in vitro release were unaffected. Similarly, the hypothalamic IR-TSH concentration and release were not altered after hypothysectomy. Chronic treatment with T4 (5 µg/100 g/day) or T3 (1.25 µg/100 g/day) decreased pituitary IR-TSH content, while hypothalamic content was increased or unaffected, respectively. Spontaneous and stimulated IR-TSH release from the pituitary decreased after chronic treatment with T3 or T4, whereas the release of IR-TSH from hypothalamic tissue was unaffected. In addition, in vitro incubation of hypothalami with thyrotropin-releasing hormone (10–5M) failed to stimulate the release of IR-TSH from hypothalamic tissue. These data indicate that hypothalamic IR-TSH does not simply represent the concentration of IR-TSH in thyrotropes of the pars tuberalis, and that the factors which regulate the synthesis and release of hypothalamic IR-TSH are different from those which regulate the release of IR-TSH from t

ISSN:0028-3835    

DOI:10.1159/000124149

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

Chronic daily administration of melatonin (MT) can have potent effects on reproduction in the hamster. Various theories have been elaborated to explain these effects but little information has been available on circulating levels of MT following MT administration. We have examined the serum MT response in the male hamster to a single dose of 25 µg MT administered in the morning or in the afternoon – the same timing and dose used by others to produce reproductive effects. With both morning and afternoon administration, serum MT increased above 1,000 pg/ml and remained above the highest basal levels during most of the 24-hour cycle. These levels are clearly supraphysiologic ones. The decline in serum MT showed two distinct components following morning administration. Half-life of the initial component which probably represents rapid distribution into tissues was 17.3 min. A half-life of 25.1 h was calculated for the second component. We conclude that use of a 25-µg dose of melatonin to study pineal effects may be mislead

ISSN:0028-3835    

DOI:10.1159/000124150

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

Clonidine, a commonly used antihypertensive agent believed to act by stimulation of central α- adrenoceptors, produced a dose-related suppression of ejaculatory behavior in sexually vigorous male rats throughout the range of treatment (0.0125–0.5 mg/kg). Treatment with 0.25 mg/kg virtually eliminated ejaculatory behavior, without altering the number of animals mounting and intromitting. These effects were maintained for at least 4 h after treatment. Prazosin, another antihypertensive (but acting by blockade of α1-adrenoceptors), increased latencies to initiation of copulation, to ejaculation, and to reinstatement of copulation following ejaculation. Additionally, prazosin (1 mg/kg) pretreatment failed to attenuate or prevent the clonidine-induced suppression of ejaculation. In contrast, yohimbine, a drug which preferentially blocks α2-adrenoceptors (2 mg/kg, 20 min prior to mating tests), caused a facilitation of copulatory behavior as evidenced by drastic decreases in ejaculation latency and intercopulatory and postejaculatory intervals. Pretreatment with yohimbine completely prevented the clonidine-induced suppression of ejaculation, while clonidine attenuated the facilitatory effects of yohimbine, suggesting a competitive interaction. These data lead to the suggestion that increased excitatory adrenergic activity results in increased sexual arousal either by blockade of α2- or stimulation of α1-adrenocep-tors. Alternatively, stimulation of α2- or blockade of α1-adrenoceptors results in diminished sexual motivation. While the precise implications of this animal research for the clinic are as yet unclear, further research could lead to important developments in the pharmacological treatment of sexual dysf

ISSN:0028-3835    

DOI:10.1159/000124151

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The objective of the present study was to determine the participation of the locus ceruleus (LC) in the regulation of the estrous cycle and of luteinizing hormone (LH) release on the afternoon of proestrus and in ovariectomized rats. Lesions of the LC on the morning of proestrus blocked the preovulatory surge of LH in the afternoon of the same day. The estrous cycle became irregular and erratic after LC lesions and displayed a prolonged period of diestrus and estrus which persisted during the entire experimental period (50 days). After this period the level of LH in the afternoon of proestrus was lower in plasma and higher in the adenohypophysis. A decrease in ovarian, uterine, and adenohypophyseal weight was also observed. LC lesions in 7-day castrated rats induced a decrease in plasma LH levels 48 und 72 h later. When these lesions were made before bilateral ovariectomy, they delayed the normal increase in plasma LH levels. From the data obtained we can conclude that lesion of the LC interferes with the cyclic as well as tonic liberation of LH. A functional rearrangement of the central noradrenergic system may occur a long time after the lesion. These effects may be mediated by connections of the LC with: (1) areas whose neurons produce gonadotropin-releasing hormone; (2) areas which in some form are involved in the liberation of gonadotropins, and (3) the median eminence.

ISSN:0028-3835    

DOI:10.1159/000124152

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The effect of exogenous progesterone (P) on the corpus luteum function (in terms of the secretion of P and 20-α-dihydroprogesterone (DHP), on the secretion of prolactin (Prl) and on the pituitary responsiveness to LHRH was studied in pseudopregnant (PSP) rats kept in alternating and constant lighting conditions (LD-PSP and LL-PSP rats, respectively). Rats were rendered pseudopregnant by appropriately timed stimulation of the cervix uteri (LL rats first received an ovulatory dose of hCG). LH responses were induced by constant rate infusion of LHRH (104 ng/hfor 21 h). P was delivered by subcutaneously inserted Silastic implants; control rats received sham implants. In both LD- and LL-PSP rats the plasma P and DHP levels were high on day 8 of PSP. On day 12, however, the plasma P levels had fallen but the DHP levels had risen, demonstrating that between days 8 and 12 functional luteolysis had occurred and that neither the production of P and DHP, nor the timing of luteolysis are under the control of the lighting conditions. On day 12 of PSP the pituitary responsiveness to LHRH was much higher than on day 8. Moreover, on days 8/9 of PSP peaks of Prl were seen in all rats, but on days 11/12 such peaks were largely absent. In LD-PSP rats ‘nocturnal’ Prl peaks were seen on days 8/9 in all 9 experimental animals, but ‘diurnal’ peaks were seen in only 4 of these animals. Also, the diurnal peaks were on average much lower than the nocturnal peaks. In LL-PSP rats we saw on days 8/9 over 24 h 2–3 irregularly timed peaks of Prl, which were not as high as the nocturnal peaks but higher than the diurnal peaks of LD-PSP rats. After implantation of two Silastic P implants into LD- and LL-PSP rats on day 6 of PSP, i.e. before functional luteolysis, the peaks of Prl and a low pituitary LHRH responsiveness were still present on day 12. Also, on day 12 the plasma concentrations of DHP were not increased in P-implanted rats. P implants inserted on day 11 (i.e. after functional luteolysis) did not prevent cessation of the appearance of Prl peaks and the rise of DHP secretion in both LD- and LL-PSP rats. Also, in LL-PSP rats which were on day 6 of PSP both ovariectomized and implanted with P, peaks of Prl were still observed on days 11/12, but in animals with sham implants peaks were absent. It thus appears that P is the corpus luteum factor which provides a permissive environment for the neural signal which causes the secretion of peaks of Prl. It is concluded that (1) during PSP and until functional luteolysis the relatively high P levels play a role in the maintenance of the secretion of peaks of Prl, and that (2) maintenance of the corpus luteum function by exogenous P (and thereby the maintenance of the state of low LHRH responsiveness) is due to P postponement of

ISSN:0028-3835    

DOI:10.1159/000124153

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

We previously reported that saturable stereospecific binding of [3H]-naltrexone in rat brain homogenates prepared from castrated male rats was greater than the corresponding binding in intact animals. We now report that we have replicated these results and that the difficulty of other investigators in observing these differences is due to methodological factors. Specifically, when samples were filtered individually and rapidly, differences between castrated and intact rats were maintained. The increase in binding was also observed when tissues were washed to remove endogenous opioids prior to incubation, when [3H]-naloxone was used as the ligand, and when various antagonists were used as displacers in the radioreceptor assay.

ISSN:0028-3835    

DOI:10.1159/000124154

出版商:S. Karger AG    

年代:1985

数据来源: Karger