- Endogenous opioid peptides are involved in feeding regulation, and alterations in opioidergic regulation have been implicated in the pathophysiology of eating disorders. To investigate further this hypothesis, we conducted a placebo-controlled study of the effect of the opiate alkaloid morphine on cortisol and prolactin secretion in six patients with anorexia nervosa and six age-matched healthy volunteers, and compared the results with those obtained in nine depressed patients. Basal cortisol but not basal prolactin levels were elevated in patients with anorexia nervosa and patients with depression. Following the administration of morphine plasma concentrations of cortisol levels declined progressively and at a similar rate in all three groups. The prolactin response to morphine was attenuated significantly in patients with depression. Neither the cortisol and prolactin response to morphine in the anorectic patients nor the cortisol response in the depressed patients we observed in this study suggests altered opiate receptor sensitivity. However, the decreased prolactin response to morphine in depressed patients remains compatible with this hypothesis.