Differential secretion of proLHRH fragments in response to [K +], prostaglandin E 2 and C kinase activation

Abstract

ProLHRH contains the luteinizing hormone-releasing hormone (LHRH) decapeptide and a 56 amino acid peptide designated gonadotropin-releasing hormone-associated peptide (GAP). We studied the effects of various known secretagogues of LHRH on the in vitro release of proLHRH fragments from the median eminence (ME) and subsequently characterized these immunoreactive products according to molecular weight (MW). GAP- and LHRH-like immunoreactive (LI) materials were secreted simultaneously into the media under basai conditions. Prostaglandin E 2 stimulated release of both peptides by approximately 2-fold. Both phorbol ester and [K + ] stimulated release of GAP-LI by 4-fold and LHRH-LI by 9-fold over baseline levels. When materials from [K +]-stimulated media were separated according to MW by high performance size-exclusion chromatography, a single peak eluted at 1300 MW in the same position as synthetic LHRH. Two GAP-LI peaks were observed. One eluted in the void volume, while the predominant peak co-eluted with synthetic rat GAP 1–56 at approximately 6500 MW. These results indicate that GAP and LHRH are co-secreted, that they are released as intact peptides, and that activation of different intracellular pathways may cause their differential secretion. These results emphasize the importance of using both in vitro and Chromatographie methodologies to evaluate the changes which may occur in LHRH prohormone processing and secretion.