Opiate receptors and anterior pituitary hormone secretion in man. Effect of naloxone infusion

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Abstract
The role of endogenous opioid receptors on anterior pituitary hormone secretion was evaluated by the administration of the opioid receptor antagonist naloxone. Naloxone infusion (8 mg i.v. followed by 4 mg/h for 3 h) did not alter basal growth hormone, prolactin and thyrotropin secretion but produced a significant rise in cortisol and gonadotropins in normal man. The infusion of the opiate antagonist appeared to increase the rate and amplitude of luteinizing hormone pulsatility. Naloxone pre-medication (10 mg i.v. 30 min before testing) did not alter the pituitary response to thyrotropin releasing hormone and luteinizing hormone releasing hormone-stimulation. Naloxone can modify basal anterior pituitary hormone secretion. This strongly suggests an endogenous opioid modulation of some of these hormones.