Alcohol effects on TRH-induced prolactin response in lactating rats: In vivo and in vitro studies

Abstract

The site of action of alcohol in inhibiting suckling-induced prolactin release in lactating rats was examined by in vivo and in vitro studies. In vivo, sulpiride- and thyrotropin-releasing hormone (TRH)-induced prolactin release was studied in lactating rats separated from their litter. On day 7, dams were implanted with an atrial catheter. On day 10, pups were removed from dams at 0800 h and, after 5 h, an extension was attached to the catheter. An hour later, a baseline blood sample was removed and was followed by sulpiride (40 μg/kg) administration. Additional blood samples were withdrawn over 1 h. After the 60-min sample, sulpiride-administered rats were infused with 0.0, 1.0, or 2.0 g/kg b.wt. alcohol. Following alcohol, a postinfusion blood sample was removed, TRH (4.0 μg/kg) was administered, and subsequent blood samples were obtained 5, 10, 20, and 30 min after TRH. For in vitro studies, cells from lactating rats in midlactation were enzymatically dissociated, plated, and on culture day 5 were exposed to 0 or 10 mM TRH. Each set of cells were additionally exposed to 0, 100, or 300 mg% alcohol and media harvested after 4 h. In a subsequent study, plated cells were exposed to increasing doses of TRH in the presence of 0, 100, or 300 mg% alcohol and media harvested as above. Prolactin in plasma (in vivo studies) and medium (in vitro studies) was measured by RIA. The results indicated that, in vivo, acute alcohol infusion failed to alter TRH-induced prolactin release in lactating rats pretreated with sulpiride. In vitro, both the basal and TRH-stimulated prolactin release was not reduced by alcohol. From these results, we conclude that anterior pituitary is probably not the site where alcohol acts to inhibit suckling-induced prolactin release in the rat.