Abstract
The effect of bradykinin (BK) on the release of β-endorphin-like immunoreactivity (β-END-LI) in rats was studied in in vivo and in vitro. Intraperitoneal injection of BK at 5 μg/ 100 g body weight resulted in a significant increase in the plasma β-END-LI level after 15 min. BK at concentrations of 10-12 - 10-7M also caused dose-dependent stimulation of β-END-LI release from the dispersed cells of the anterior pituitary of rats. On gel chromatography, the β-END-LI released by incubation of the cells with 10-7M BK separated into two components; one eluted in the same positions as human β-lipotropin and the other as human β-endorphin. BK did not stimulate β-END-LI release in Ca++-free medium. Addition of 10-3M verapamil, 10-6M dexamethason or 10-7M somatostatin to the incubation medium inhibited BK-induced β-END-LI release from the cells. Ouabain (10-5M) also stimulated β- END-LI release, but its effect was not additive with that of BK. These results indicate that BK stimulates β-END-LI release and that calcium ion is involved in the mechanism of this effect.
