Phorbol esters stimulate in vitro gnrh release from the hypothalamus of the estrogen- primed, ovariectomized rat: Inhibitory effects of cocaine

The purpose of this study was (1) to characterize more fully the effects of phorbol esters to stimulate GnRH release in vitro and (2) to determine whether cocaine (which disrupts estrous cyclicity in rats) affected phorbol ester stimulation of GnRH release in vitro. Hypothalami were collected from ovariectomized rats injected subcutaneously with 50 pg/kg of 17(3-estradiol benzoate the two previous mornings. Sagittal sections of this block of CNS tissue comprising the preoptic area/anterior hypothalamus and mediobasal hypothalamus/median eminence were perfused at a rate of 6.2 ml/h with a modified Krebs-Ringer buffer (pH 7.4) using a programmable perfusion system. Perfusion results showed that 10-min pulses of phorbol 12-myristate 13-acetate or phorbol 12,13-dibutyrate (PDBu) increased GnRH release in dose-dependent fashion (10_1° to 10"6 M) but had no effect on aminergic transmitter release. The biologically inactive a-phorbol was without effect on GnRH release. PDBu-stimulated GnRH release was blocked by both tetrodotoxin and cocaine, known inhibitors of Na+ influx. These results suggest a role for protein kinase C in regulating the release of GnRH. Our results that cocaine and tetrodotoxin attenuated phorbol ester stimulation of GnRH, presumably through inhibition of Na+ influx, suggest a direct biochemical mechanism for cocaine disruption of hypothalamic GnRH secretion and, consequently, cyclic reproductive function.