Cell swelling induced by medium hyposmolarity or isosmolar urea stimulates gonadotropin-releasing hormone secretion from perifused rat median eminence

Abstract

Medium hyposmolarity between 10 and 50% and isotonic urea between 22.5 and 90 mM induced a dose-dependent burst of gonadotropin-releasing hormone (GnRH) secretion from perifused median eminence tissue which was maximal at 2–3 min and returned to near baseline by 5 min in spite of continued exposure to the stimulus. If Ca 2+-free medium was used, osmotic stimulation of secretion was increased or unchanged, but secretion induced by 30 mM K + was markedly reduced. Our data indicate that cell swelling induced by medium hyposmolarity or permeant molecules stimulates GnRH secretion from median eminence cells or cell processes as it does secretion from normal endocrine cells containing hormone stored in intracellular vesicles. In both, Ca 2+ influx is not required or has a negative modulating influence on cell swelling-induced secretion.