Trypsin-like activity of rat anterior pituitary in relation to secretory activity

Effects of Org OD 14 on pituitary and peripheral beta-endorphin in castrated rats and post-menopausal women

The aim of the first part of this study was to evaluate the effects of a new synthetic steroid (7 alpha,17 alpha)-17-hydroxy-7-methyl-19-norpregn-5(10)-en-20-yn-3-one (Org OD 14), on anterior pituitary (AP) and neurointermediate pituitary lobe (NIL) contents and on circulating levels of beta-endorphin (beta-EP) in rats. Three weeks after ovariectomy, groups of 9 rats were treated with either Org OD 14 (2 or 10 micrograms/day/rat for 14 days) or a placebo. In addition, 2 groups of ovariectomized rats were also treated with oestradiol benzoate (EB) (2 or 10 micrograms/day/rat for 14 days) to compare the effectiveness of the new steroid with that of a classical oestrogenic substance. beta-Ep concentrations were measured in plasma and in AP and NIL extracts by means of double-antibody radioimmunoassay (RIA), employing a specific anti-camel beta-EP (C-terminal fragment). Both doses of Org OD 14 induced a significant dose-related increase in plasma and pituitary lobe beta-EP concentrations as compared with the results on placebo treatment. By comparison, EB was active only at a dose of 10 micrograms/day. Despite the common stimulatory effects of EB and Org OD 14 on pituitary beta-EP, these findings suggest that the two steroids have different modes of action. The second part of the study investigated the changes in beta-EP and beta-lipotrophin (beta-LPH) plasma levels in a group of post-menopausal women treated for 6 months with Org OD 14 (2.5 mg/day) in comparison with the levels in a placebo-treated group. The clinical efficacy of Org OD 14 treatment in post-menopausal symptoms was confirmed, as well as its lack of or only transient effect on plasma lipids and lipoproteins. beta-EP and beta-LPH plasma levels were significantly higher in the Org OD 14-treated group than in the placebo group as from the second month until the end of the observation period.

Anterior pituitary glandular kallikrein: trypsin activation and estrogen regulation

Discrepant reports exist regarding the presence of glandular kallikrein or other trypsin-like serine proteases in the pituitary. The existence of pituitary kallikreins in latent forms could explain these discrepancies. I report that trypsin treatment of rat anterior pituitary homogenates activates two serine proteases which generate kinins from kininogen and selectively cleave chromogenic substrates for kallikreins. One protease (enzymatically and immunologically resembling glandular kallikrein) and activated 5-fold by trypsin and was 20 times more abundant in female than in male lobes due to hormonal regulation by ovarian estrogens. The second kallikrein (activated 20-fold by trypsin) was unaffected by estrogens. The results demonstrate that rat anterior pituitary kallikreins predominantly exist in latent forms requiring activation for detection. Additionally, glandular kallikrein is a major estrogen-induced protein in the rat anterior pituitary. No other member of this large protease family is known to be regulated by estrogens.

Various proteinase inhibitors decrease prolactin and growth hormone release by anterior pituitary cells

Proteinase inhibitors were tested for their ability to inhibit prolactin (PRL) and growth hormone (GH) release by cultured anterior pituitary cells of the rat. Inhibitors of microbial origin (chymostatin, elastatinal, leupeptin) had either no or a moderate effect on hormone release while some tripeptide aldehydes, especially those with lysine at their C terminus, inhibited markedly PRL and to a lesser extent GH release. Boc-DPhe-Phe-lysinal was the most effective on lactotrophs inhibiting PRL release more than 50% at 10(-4) M. The site(s) of action of tripeptide aldehydes remain to be elucidated.

Loss of sensitivity to morphine induced by prolonged ACTH treatment

The effect of long term ACTH treatment on some actions of morphine were studied. The effect of ACTH administration was compared to that induced by acute dexamethasone injection. ACTH caused a delayed inhibition of the morphine induced increase in growth hormone secretion demonstrable 24 hr after the last hormone injection. The morphine induced increase of striatal DOPAC (3,4-dihydroxyphenylacetic acid) content was also inhibited by ACTH treatment, however, neither the analgesia, nor the hypermotility caused by morphine were affected. Dexamethasone did not alter significantly the responsiveness to morphine. It is concluded that the prolonged exposure to ACTH presumably causes a corticosterone-mediated loss of responsiveness of functionally restricted opiate sensitive mechanisms in the central nervous system.

A serine-proteinase inhibitor (Boc-D-Phe-Pro-Arg-H) inhibits the secretion of adrenocorticotropin- and beta-endorphin-immunoreactive peptides in vitro

The effects of a potent serine protease inhibitor, Boc-D-Phe-Pro-Arg-H, on the secretion and content of ACTH and beta-endorphin-like immunoreactivities of cultured rat anterior pituitary cells were studied. Basal release of the hormones was not affected by the drug but secretion in response to stalk-median eminence extracts was inhibited. The inhibitor did not effect the amount of ACTH or beta-endorphin in the medium plus the cells, nor did it change the ratio of the lipotropin and beta-endorphin-like immunoreactivities. Thus the compound seems to affect the release of ACTH and beta-endorphin, but not the processing of lipotropin to beta-endorphin.