Gonadotropin-Releasing Hormone Release from the Rat Hypothalamus: Dependence on Membrane Depolarization and Calcium Influx*

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Abstract
Release of gonadotropin-releasing hormone (GnRH) was studied by incubating individual rat hypothalami for 60 min, after a 30-min preincubation period, and measuring GnRH in the medium by immunoassay. During the 1 h of incubation, endogenous GnRH release was linear and exogenous GnRH was not destroyed. Membrane depolarization produced by increasing the medium potassium concentration to 60 mM increased GnRH release to 200–500% of control. Membrane depolarization produced by adding 10-5 or 10-4 M ouabain increased GnRH release to 200% of control. Melatonin (10-7 M) and prostaglandin E2 (4 × 10-4 M) also stimulated GnRH release to 200% and 170% of control, respectively. Inhibition of calcium influx by omission of medium calcium and addition of 0.05 M EDTA reduced GnRH release to 50% of control. Both no calcium-EDTA medium and verapamil (10-5 M) prevented the stimulation of GnRH release by 60 mM potassium, 10-3 M melatonin, and 4 × 10-4 M prostaglandin E2. We conclude that hypothalamic GnRH release depends on membrane depolarization and calcium influx, as does the secretion of hormones from other endocrine tissues.