The effect of clonidine on hormone release mediated through activation of opiate receptors

To elucidate the mechanism of clonidine's effect on hormone release, serum growth hormone (GH), luteinizing hormone (LH), cortisol, and plasma beta-endorphin concentrations were determined after clonidine, naloxone, or the combined therapy of clonidine plus naloxone in six healthy women investigated in the luteal phase of their menstrual cycles. The clonidine injection increased GH levels. Naloxone (0.05, 0.1, and 0.2 mg/kg) decreased serum GH concentrations. Naloxone also increased serum LH, whereas clonidine decreased LH levels. Only the maximal dose of naloxone significantly increased serum cortisol concentrations. Clonidine had opposite effects on cortisol levels. These results demonstrate that combined therapy with clonidine plus naloxone leads to inhibition of the response of GH, LH, and cortisol to clonidine injection.