Corelease of Dynorphin-Like Immunoreactivity, Luteinizing Hormone, and Follicle-Stimulating Hormone from Rat Adenohypophysisin Vitro*

Abstract

Rat anterior pituitary quarters or actuely dispersed rat anterior pituitary cells were incubated in vitro, and the release of dynorphin A1-13-like immunoreactivity (Dyn A1-13-IR) into the incubation medium was studied. Addition of LHRH led to a concentration-dependent enhancement of the release of Dyn A1-13-IR with a maximum secretory rate which was about 4-fold higher than basal secretion. Dyn A1-13-IR was released by LHRH concomitantly with LH [luteinizing hormone] and FSH, and the concentration-response relationships as well as the time course were virually identical. Gel filtration and HPLC [high performance liquid chromatograph] revealed a single peak of Dyn A1-13-IR, with an apparent MW of about 6000. In addition to Dyn A1-13-IR, .alpha.-neo-endorphin-like immunoreactivity was released by LHRH. The LHRH-stimulated release of Dyn A1-13-IR was mimicked by the LHRH analog D-Ala6,des-Gly10-LHRH ethylamide and blocked in a competitive manner by the LHRH anatagonist D-p-Glu1,D-Phe2,D-Trp3,6-LHRH. Addition of TRH (5 .mu.M), rat corticotropin-releasing factor (100 nM), arginine vasopressin (1 .mu.M), or synthetic human pancreatic GH[growth hormone]-releasing hormone (10 nM) produced no effect on Dyn A1-13-IR release. An extract of the rat medial basal hypothalamus stimulated the release of Dyn A1-13-IR and .beta.-endorphin-like immunoreactivity, and the former, but not the latter, effect was blocked by the LHRH antagonist D-pGlu1,D-Phe2,D-Trp3,6-LHRH. Apparently, dynorphin-like materal and other proenkephalin B-derived peptides are released concomitantly with LH and FSH from rat adenohypophysis in vitro upon activation of LHRH receptors. Apparently, proenkephalin B-derived peptides coexist with LH- and/or FSH in at least some gonadotrophs of the normal rat anterior pituitary gland.