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 micrograms/kg of 17 beta-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(-10) to 10(-6) M) but had no effect on aminergic transmitter release. The biologically inactive alpha-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.
King
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Department of Cellular and Structural Biology, University of Texas Health Science Center, San Antonio 78284.
Kang
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Javors
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Schenken
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D000818:Animals; D003042:Cocaine / Q000494:pharmacology*; D004298:Dopamine / Q000032:analysis; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D066298:In Vitro Techniques; D009638:Norepinephrine / Q000032:analysis; D010052:Ovariectomy; D010053:Ovary / Q000502:physiology*; D010703:Phorbol Esters / Q000494:pharmacology*; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000032:analysis; D013779:Tetrodotoxin / Q000494:pharmacology
D010703:Phorbol Esters; D012701:Serotonin; D007987:Gonadotropin-Releasing Hormone; D013779:Tetrodotoxin; D004958:Estradiol; D003042:Cocaine; D004298:Dopamine; D009638:Norepinephrine