Properties of LHRH release from a hypothalamic synaptosomal fraction of estrogen-primed ovariectomized rats.

The release of luteinizing hormone-releasing hormone (LHRH) from mitochondrial-synaptosomal fractions (P2) of basomedial hypothalamus was examined under various conditions. Less than 3% of the LHRH in P2 suspensions was released under control conditions while the addition of 60 mM KCl or NaCl effected an 8-fold increase in LHRH as measured by radioimmunoassay. Equiosmolar sucrose effected only a 1.8-fold increase in LHRH release. The stimulatory effects of both Na+ and K+ were significantly inhibited by Mn2+ or La3+. Two forms of released LHRH were observed, one soluble and the other particulate. Soluble LHRH release was effected by hypertonic sucrose or 60 mM KCl and was not inhibited by Ca2+ antagonists. The release of particulate LHRH was unaffected by hpertonic sucrose, was stimulated 10-fold by 60 mM KCl, and was abolished with Ca2+ antagonists. These results suggest that the released soluble LHRH results from nonspecific leakage while the release of particulate LHRH reflects a Ca2+-dependent secretory process.