Interferon-gamma inhibits stimulated adrenocorticotropin, prolactin, and growth hormone secretion in normal rat anterior pituitary cell cultures

Preincubation of rat anterior pituitary (AP) cells with homologous interferon-gamma (IFN-gamma) caused a dose-dependent inhibition of ACTH secretion stimulated by CRF. The effect was seen in both monolayer and aggregate AP cell cultures and was not due to cytotoxicity. In monolayer cultures IFN-gamma also inhibited PRL and GH release stimulated by various hypothalamic releasing factors. IFN-gamma did not affect the time kinetics of the ACTH response to CRF. The dose needed for half-maximal inhibition amounted to approximately 1 (antiviral) U/ml. The effect of IFN-gamma was abrogated by an IFN-gamma-neutralizing monoclonal antibody. Furthermore, ACTH secretion by the AP cells was not affected by the anti-IFN-gamma antibody added alone, indicating that in the culture system no endogenous IFN-gamma is operational in regulating the ACTH response studied. Of the other cytokines tested [interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and interferon-alpha/beta (IFN-alpha/beta)] only TNF-alpha and IL-6 were found to inhibit CRF-stimulated ACTH release, although this inhibition was less pronounced than that caused by IFN-gamma. Lipopolysaccharide, even at high doses, did not significantly inhibit the ACTH response to CRF. These results identify IFN-gamma as one of the inflammatory cytokines that, like IL-1, TNF-alpha, and IL-6, have the potential to regulate pituitary function.     

Biphasic action of forskolin on growth hormone and prolactin secretion by rat anterior pituitary cells in vitro.

To assess the role of cAMP-mediated signal transduction processes in mediation of secretagogue-stimulated GH release, we examined the dose-related effects of the diterpene adenylate cyclase activator forskolin (FSK) in primary monolayer cultures of rat adenohypophyseal cells. In cell cultures prepared from both immature (12 days old) and adult (6 weeks to 4 months old) male or female rats, the dose-related stimulation of GH release by FSK was biphasic. With increasing FSK concentrations from 0.03-3.16 microM, GH release increased progressively to maximal values of 442 +/- 19% and 303 +/- 10% of basal release in cells from immature and adult rats, respectively. FSK concentrations above 3.16 microM induced progressively diminished GH responses, with net inhibition to below basal release evident at 100 microM FSK. FSK stimulated PRL release to a lesser degree than it did GH release; the PRL response to FSK was also biphasic. When maximal stimulatory concentrations (Emax) of FSK and GH-releasing factor (GRF; 10 nM) were added in combination, the GH response was significantly less than the individual response to either secretagogue alone. In response to FSK alone, GRF alone, and FSK plus GRF, GH release was 478 +/- 7%, 583 +/- 11%, and 244 +/- 5%; 278 +/- 4%, 283 +/- 3%, and 175 +/- 2%; and 299 +/- 12%, 351 +/- 5%, and 191 +/- 17% of basal release in cells from 12-day-old, adult male, and adult female rats, respectively (P less than 0.01 for all responses to combined addition vs. the individual responses). Submaximal stimulatory concentrations of GRF added in combination with submaximal FSK elicited partially additive GH responses; the GH response to Emax GRF, on the other hand, was inhibited in a dose-related manner by all concentrations of FSK that by themselves were stimulatory. The GH responses were also suppressed when Emax FSK was added to cultured cells of 12-day-old rats in combination with Emax cholera toxin (2.5 ng/ml) or prostaglandin E2 (10 microM), agents whose actions, like that of GRF, involve adenylate cyclase activation. In contrast, FSK did not suppress but in most cases augmented the maximal GH responses to secretagogues whose action is independent of adenylate cyclase activation: (Bu)2cAMP (0.5 mM), TRH (100 nM), phorbol myristate acetate (50 nM), the Ca2+ ionophore A23187 (250 microM), and the dihydropyridine Ca2+ channel agonist BAY K8644 (10 microM). Indeed, combined addition of FSK with the latter two agents resulted in synergistic stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of environmental osmolality on release of prolactin,growth hormone and ACTH from the tilapia pituitary

Prolactin (PRL) plays a central role in freshwater (FW) adaptation in teleost fish. Evidence now suggests that growth hormone (GH) acts in the seawater (SW) adaptation in at least some euryhaline fish. Reflecting its important role in FW adaptation, plasma levels of PRL(188) and PRL(177) are higher in tilapia (Oreochromis mossambicus) adapted to FW than in those adapted to SW. A transient but significant increase in plasma GH was observed 6h after transfer from FW to SW. Elevated plasma PRL levels were seen in association with reductions in plasma osmolality after blood withdrawal in FW fish whereas no significant change was seen in plasma GH levels. When pituitaries from FW tilapia were incubated for 7 days, secretion of both PRLs was significantly greater in hyposmotic medium than in hyperosmotic medium for the first 24h. Secretion of GH from the same pituitary was relatively low during this period compared with PRL secretion. No consistent effect of medium osmolality on GH release was seen for the first day, but its cumulative release was increased significantly in hyperosmotic medium after 2 days and thereafter. On the other hand, ACTH release was extremely low compared with the secretion of PRLs and GH and there was no consistent effect of medium osmolality. These results indicate that PRL release from the tilapia pituitary is stimulated both in vivo and in vitro as extracellular osmolality is reduced, whereas the secretion of GH increases temporarily when osmolality is increased. ACTH seems to be relatively insensitive to the changes in environmental osmolality.     

Purinergic regulation of bradykinin-induced plasma extravasation and adjuvant-induced arthritis in the rat.

We assessed the contribution of ATP and adenosine (i) to a major sign of acute inflammation, plasma extravasation (PE), in the rat knee joint and (ii) to the severity of joint injury in adjuvant-induced experimental arthritis, a chronic inflammatory disease. PE induced by local infusion of bradykinin, which we have previously shown to depend on the sympathetic postganglionic neuron terminal, was markedly enhanced by coinfusion of either ATP or the adenosine A2-receptor agonist 2-[4-(2-carboxyethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenos ine. Bradykinin-induced PE was inhibited by coinfusion of the ATP receptor antagonist adenosine 5'-[alpha,beta-methylene]triphosphate, the A2-receptor antagonist 3-(5H-thiozolo[2,3b]quinazolin-3-yl)phenol monohydrochloride, or the adenosine A1-receptor agonist N6-cyclopentyladenosine. The joint injury associated with experimental arthritis, which is reduced in severity in sympathectomized rats, was also markedly attenuated by daily administration of either ATP (40% reduction) or adenosine (55% reduction). These results demonstrate that the purines ATP and adenosine (acting at the A2 receptor), cotransmitters in the sympathetic postganglionic neuron terminal, enhance bradykinin-induced sympathetic postganglionic neuron terminal-dependent PE but inhibit the joint injury of arthritis. These opposing purinergic effects on PE and joint injury suggest that enhanced PE protects against joint injury.     

Effect of long-term corticosteroid administration on rat pituitary growth hormone and prolactin

In vitro corticosteroids stimulate GH synthesis by pituitary cells, while in vivo they suppress stimulated plasma GH levels. In this study we investigated in rats the effect of hydrocortisone administration for 2-4 weeks on pituitary GH content. Hydrocortisone added to the drinking water (100 mg/l) resulted in a marked stimulation of pituitary GH content after 3 and 4 weeks of treatment. No significant stimulation, however, was observed on basal GH release by the pituitary gland incubated in vitro. Further, we found that both Prl content and release were inhibited by hydrocortisone administration.     

Differential effects of ketoconazole on prolactin and growth hormone release by normal and tumoral rat anterior pituitary cells in vitro

The imidazole derivative ketoconazole (1-100 microM) was shown to stimulate the release of prolactin (PRL) from rat anterior pituitary cells in vitro. In contrast, this drug did not affect growth hormone (GH) release from the same cells. In addition, ketoconazole was found to have no effect on PRL or GH release from a tumoral pituitary cell clone (GH3). Treatment of normal pituitary cells with ketoconazole (10 microM) for more than 20 min abolished TRH-induced hormone release. TRH-stimulated release was both attenuated and delayed in the ketoconazole-treated tumoral cells. Ketoconazole (10 microM) did not affect the basal electrophysiological properties of GH3 cell membranes, although it did affect the TRH-induced response. The action of ketoconazole of the spontaneous release of PRL by normal cells and the TRH-stimulated release of PRL and GH is consistent with an interference with arachidonic acid metabolism.     

Immunoreactive alpha-MSH and ACTH levels in rat plasma and pituitary.

A radioimmunoassay is described for the measurement of alpha-melanocyte-stimulating hormone (alpha-MSH). The antibody was produced in rabbits by immunization with alpha-MSH coupled to bovine serum albumin with carbodiimide. The antibody did not react significantly with ACTH, beta-MSH, or 6 fragments of ACTH. The sensitivity and reliability of the assay were improved by employing a simple plasma extraction procedure. When applied to a 2 ml plasma sample, the detection limit of the radioimmunoassay was 6 pg/ml. ACTH was measured with a sensitive and specific radioimmunoassay previously described for humans and adapted for the rat. The anti-ACTH serum cross-reacted with the biologically active portion of alpha-p ACTH and not with alpha-MSH, beta-MSH or the alpha-p 17-39 and alpha-p 25-39 fragments of ACTH. The detection limit was 20 pg/ml. Plasma and pituitary alpha-MSH and ACTH had the same immunoreactivity as synthetic alpha-MSH and ACTH. alpha-MSH and ACTH contents of the rat neurointermediate lobe were 1398 +/- 360 (SE) ng and 28.2 +/- 2.9 ng, respectively, while in the anterior lobe they were 102 +/- 31 ng and 551 +/- 36 ng, respectively. The plasma alpha-MSH concentration at 8 AM in male rats was 64 +/- 8 pg/ml when the plasma ACTH concentration was 92 +/- 15 pg/ml. Over a 24-hour period two peaks of plasma alpha-MSH were observed, one at 4 AM (142 +/- 35 pg/ml) and the other at 4 PM (139 +/- 26 pg/ml). Plasma ACTH was higher at noon (151 +/- 43 pg/ml) and 4 PM (130 +/- 48 pg/ml). Short-term exposure to ether induced a transient increase in alpha-MSH level 5 min later and a rapid return to normal levels. Plasma ACTH increased significantly 2.5 min after the onset of ether stress and remained high for 30 min. Two hours' exposure to ether did not change plasma alpha-MSH, although a 3-fold increase in plasma ACTH was observed. Haloperidol injection was followed by a large increase in plasma alpha-MSH, whereas ACTH levels increased similarly after saline and Haloperidol injection. Corticoid administration reduced ACTH, but not alpha-MSH. Three weeks after adrenalectomy, alpha-MSH levels had not changed but ACTH levels had increased ten-fold. These data indicate that alpha-MSH is secreted in the rat, and that the regulation of its secretion is different from that of ACTH.     

Cytological changes in prolactin, ACTH, and growth hormone cells of the pituitary gland of Pungitius pungitius L. in response to increased environmental salinities.

Adult, nine-spined sticklebacks, Pungitius pungitius, were gradually transferred from fresh water to dilute and full strength seawater for periods of 10 hr, 3, 6, 9, and 21 days. Light microscopy studies of the pituitary gland revealed unusual and marked changes in the prolactin, ACTH, and GH cells of the adenohypophysis. In at least some animals from all experimental groups there were intercellular cysts among the prolactin cells. These became so large in the 21-day group as virtually to obliterate the RPD. In view of the enormous size of some cysts and the great diminution in prolactin cell numbers, they were presumed to be signs of decreased secretory activity. Transfer of animals from fresh water to dilute and full strength seawater was generally associated with decreased nuclear diameters in prolactin, ACTH, and GH cells. The GH cells were markedly degranulated in all animals from the 21-day seawater group. Evidently the euryhaline members of the Gasterosteidae show widely differing pituitary responses to altered ambient salinities.