Abstract
The effect of clonidine, a central α-adrenergic agonist, on the suppression of LH release induced by β-endorphin or FK33-824, an endogenous opioid peptide or its synthetic analog, was investigated in castrated male rats, with or without pretreatment with reserpine. Pulsatile LH secretion was inhibited by intravenous injection of FK33-824 (400μg/kg), or intraventricular injection of β-endorphin (5μg). Without pretreatment with reserpine, intraperitoneal administration of clonidine (1mg/kg) failed to reverse the inhibition of LH release induced by these peptides. However, with pretreatment with reserpine (10mg/kg), clonidine abolished the inhibitory effect on LH secretion induced by these peptides in castrated male rats. These data indicate that, unlike the results in ovariectomized, steroid-primed rats, pretreatment with reserpine allows the α-adrenergic system to act more peripherally than the opioid neuronal system in a neuronal network-regulating LH release in castrated male rats.
