Release of dynorphin-like immunoreactivity from rat anterior pituitary gland in vitro

Rat anterior pituitary quarters were incubated in vitro and the release of dynorphin A_1-13-like immunoreactivity (Dyn A_1-13-IR) into the incubation medium was studied. An elevation of the potassium concentration of the incubation medium to 40 mmol/l increased the release of Dyn A_1-13-IR in a calcium-dependent manner. Addition of luteinizing hormone-releasing hormone (LHRH) stimulated the release of Dyn A_1-13-IR in a dose-dependent manner. The LHRH-induced release of Dyn A_1-13-IR was almost completely prevented by omission of calcium ions from the incubation medium or by addition of the LHRH-antagonist d-pGlu¹, d-Phe², d-Trp^3,6-LHRH. This is the first demonstration that dynorphin-like immunoreactivity can be released from the rat adenohypophysis through calcium-dependent mechanisms by both high potassium concentration and receptor-mediated stimulation.