[In vivo and in vitro effects of histamine on the release of beta-endorphin-like immunoreactivity].

The effect of histamine on the release of beta-endorphin-like immunoreactivity (beta-END LI) in rats was studied in vivo and in vitro experiments. Intravenous injection of 100 micrograms/100g BW of histamine resulted in a significant increase in the plasma beta-END-LI level 5, 15 minutes after the injection. Histamine at concentrations of 10(-12) to 10(-9)M also caused dose-dependent stimulation of release of beta-END-LI from the dispersed cells of the anterior pituitary of rats. On gel-chromatography, the beta-END-LI released by incubating the cells with 10(-9)M histamine consisted of two components, which eluted in the same positions as human beta-lipotropin and human endorphin, respectively. Addition of 2mM CoCl2 to the incubation medium inhibited histamine-induced beta-END LI release from the cells. Histamine H1 receptor antagonist (10(-6)M) inhibited histamine-induced beta-END-LI release from the cells. Histamine H2 receptor antagonist (10(-6)M), however, did not inhibit histamine-induced beta-END-LI release. These results indicate that histamine acts directly on the anterior pituitary cells to stimulate beta-END-LI release and that calcium ion is involved in the mechanism of this effect.