Mechanism of Action of Dopamine on the in Vitro Release of Gonadotropin-Releasing Hormone

Controversy exists on whether dopamine (DA) stimulates or inhibits GnRH secretion and whether its effects are mediated via α-adrenergic receptors or dopaminergic receptors. As a means to examine this conflict, we have utilized an in vitro superfusion system to study the effects of DA, norepinephrine (NE), phentolamine (μ-antagonist), pimozide (DA antagonist), and two DA agonists (apomorphine and bromocryptine) on GnRH release from isolated mediobasal hypothalami from adult male rats. In this dynamic system, graded concentrations of both NE and DA (2.0 nm to 2.0 μm) led to a dose-dependent increase in GnRH output during the 10 min interval that followed each pulse dose of NE (P < 0.02). or DA (P < 0.05). The DA-induced GnRH release was reproducible, consistent, and significant over five successive pulses (20 μm) at 30-min intervals (P < 0.02). Coinfusion of phentolamine (20 nM) prevented the DA (20 MM) induced release of GnRH (P < 0.03), but pimozide (20 nM) had no significant effect on DA-induced GnRH rel...