Evidence for hypothalamic noradrenergic involvement in naloxone-induced stimulation of luteinizing hormone release

A single injection of the opiate antagonist, naloxone (NAL), resulted in a fourfold increase in serum luteinizing hormone (LH) concentration 20 min after injection. To determine whether noradrenergic neurons were involved, male Sprague-Dawley rats were treated with alpha-methyl-p-tyrosine (alpha-MPT), phenoxybenzamine hydrochloride (PBH), or diethyldithiocarbamate (DDC), all anti-noradrenergic drugs. Reduction of hypothalamic norepinephrine synthesis by alpha-MPT or DDC, or blockade of the alpha-receptors by PBH, resulted in complete suppression of NAL-induced LH release. These results suggest that the NAL-induced increase in LH release is mediated in part via a hypothalamic noradrenergic mechanism.