摘要:

In this study we evaluated the quantitative influence of GRF and TRH on the rate of hormone secretion from single cells in cultures of male pituitaries. To accomplish this, we dispersed pituitaries from male rats with trypsin and cultured them for 24 or 48 h. Reverse hemolytic plaque assays for GH and prolactin were then performed on retrypsinized cultures to identify individual cells that secreted these hormones. Mammotropes and somatotropes were found to comprise 31.4 ± 1.8 and 32.2 ± 0.9% (mean ± SE, n = 3 experiments), respectively, of all cells in 24-hour cultures. Immunocytochemical staining of different batches of cells from the same dispersions corroborated the proportions of these two cell types. Differences in the rate of basal hormone secretion were observed within each of these cell populations as evidenced by the gradual appearance of prolactin and GH plaques over a 4-hour period when incubations were conducted in the absence of stimulatory secretagogues. Addition of increasing concentrations of GRF (1 × 10–10–1 × 10–7M) orTRH (1 × 10–9–1 × 10–6M) to these incubations resulted in dose-related increases in the rate of GH and prolactin plaque formation, respectively. Maximal plaque development by somatotropes could be induced within 30 min of administering large doses of GRF, indicating that most, if not all somatotropes are responsive to this secretagogue. In contrast, approximately one third of all mammotropes could not be stimulated to form plaques acutely when subjected to similar treatment with TRH. This observation suggests that mammotropes are heterogeneous with respect to TRH responsiveness. Finally, treatment with these secretagogues did not increase over the control value the percentage of all cultured cells that formed plaques, demonstrating that the hypothalamic factors tested did not recruit additional cells into the secretory pool. These results provide evidence to indicate that: (1) mammotropes may account for a greater proportion of pituitary cells in males than previously believed; (2) mammotrope and somatotrope populations in male rats are each heterogeneous with respect to basal hormone secretion, and that mammotropes differ in responsiveness to TRH, and (3) the rate of plaque formation provides a reliable index of the rate of hormone secretion. Thus, the reverse hemolytic plaque assay provides a semiquantitative tool for studying hormone release by individual pituitar

ISSN:0028-3835    

DOI:10.1159/000124250

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

No immunoreactive axons were detected with an antiserum against tyrosine hydroxylase in the rabbit intermediate lobe (IL), which thus appears to be devoid of dopaminergic (DA) innervation. Dopamine and its agonists, which classically inhibit α-MSH release have no inhibitory effects on rabbit IL superfused in vitro but, paradoxically, stimulate α-MSH release. D2 type DA receptors, known to mediate inhibitory control of dopamine on melanotropic cells, and detectable by their affinity for (3H)-spiroperidol, were as previously reported absent from the rabbit IL. The absence of (3H)-spiroperidol binding sites in the IL was further confirmed on rabbit pituitary sections by radioautography. The mechanism of DA stimulation is still not clear, but might be tentatively explained by interference with other receptors involved in the stimulation of the gland. The lack of DA inhibitory control over the rabbit IL is an exception among the species so far studie

ISSN:0028-3835    

DOI:10.1159/000124251

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

The effects of bremazocine and U-50,488, two selective opioid Kreceptor agonists, and the preferential µ receptor agonist morphine on the secretion of PRL and GH were compared in conscious male rats bearing permanent right atrial cannulae for serial blood sampling and drug delivery. All three opioids stimulated PRL secretion in a dose-related manner, but the Kagonists differed from morphine in several respects. They were considerably more potent than morphine in triggering a PRL response, but were unable to elevate PRL levels to more than 100 ng/ml, whereas morphine, at the highest dose (4.5 mg/kg), induced an almost twice larger response. Also their PRL-releasing effect was inhibited more strongly by the preferential Kreceptor antagonist Mr-2266 than by naloxone, whereas Mr-2266 and naloxone, which are equipotent as antagonists of the µ receptors, were equipotent in suppressing the PRL-stimulating effect of morphine, a µ agonist. In a complete contrast to morphine, which effectively stimulated GH secretion, the Kagonists had no effect on GH release at lower doses and suppressed it at higher doses. It is concluded that the PRL-releasing effect of the Kagonists is mediated by the Kreceptors which may participate with the µ receptors in regulation of PRL secretion by opioids. The GH-inhibiting effect of the Kagonists requires further clarificat

ISSN:0028-3835    

DOI:10.1159/000124252

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

An analysis of the GH release-inhibiting action of the opioid Kreceptor agonists bremazocine and U-50,488, established earlier, was attempted by testing the agonists against activation of GH secretion by morphine or clonidine in male rats bearing right atrial cannulae for serial blood sampling and drug delivery. Both ĸ agonists inhibited the effect of subsequent administration of clonidine in a dose-related manner. Bremazocine was approximately ten times more potent than U-50,488, a ratio corresponding to the known affinities of the two compounds for the ĸ receptors. The inhibiting action of bremazocine was more strongly reversed by the preferential ĸ receptor antagonist Mr-2266 than by naloxone, neither of which interfered with the GH-stimulating effect of clonidine. Bremazocine, however, did not alter the activation of GH secretion by exogenous growth hormone releasing factor. Thus, the inhibiting effect of bremazocine and probably U-50,488 seems to be derived from stimulation of the ĸ receptors which in turn activates a GH release inhibiting mechanism of unknown identity which, however, does not involve release of somatostatin. Both Kagonists also inhibited the effect of morphine, but in this case U-50,488 was approximately hundred times less effective than bremazocine. Since bremazocine and U-50,488 are antagonists of the ĸ receptors, which seem to mediate the GH-releasing effect to morphine, their inhibiting effect in this instance may be related to this property rather than to an action on the ĸ receptors. Bremazocine, but not U-50,488, was also highly effective in inhibiting stimulation of PRL secretion by morphine. Stimulation of PRL by morphine is mediated by the µi type of opioid receptors, and the inhibiting effect of bremazocine may reflect its antagonist action on these receptors not shared by U-50,488. In conclusion, our data indicate that the ĸ receptors may participate in the regulation of GH secretion conveying an inhibitory influence. They also demonstrate the complexity of actions of the Kreceptor agonists derived from their multiple and varied interactions with the different recepto

ISSN:0028-3835    

DOI:10.1159/000124253

出版商:S. Karger AG    

年代:1986

数据来源: Karger

摘要:

Colchicine treatment reveals a population of vasoactive intestinal polypeptide (VIP) positive cell bodies in the hypothalamic paraventricular nucleus (PVN) of the vasopressin-deficient Brattleboro rat. These immunoreactive perikarya in the PVN cannot be detected in colchicine-treated Long-Evans animals. When Brattleboro rats are administered vasopressin, there is a significant decrease in the number of VIP-immunopositive cell bodies in the PVN. Evidently, an alteration in the synthesis and/or release of VIP occurs in the absence of the antidiuretic hormone.

ISSN:0028-3835    

DOI:10.1159/000124254

出版商:S. Karger AG    

年代:1986

数据来源: Karger

ISSN:0028-3835    

DOI:10.1159/000124255

出版商:S. Karger AG    

年代:1986

数据来源: Karger