The Role of Endogenous Opiates in the Mechanism of Inhibited Luteinizing Hormone (LH) Secretion in Women with Anorexia Nervosa: The Effect of Naloxone on LH, Follicle-Stimulating Hormone, Prolactin, and β-Endorphin Secretion*

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Abstract
The aim of this study was to evaluate the role of endogenous opiates in the mechanism of decreased LH secretion in women with anorexia nervosa. For this purpose the effect of opiate receptor blockade with naloxone on LH, FSH, PRL, and β-endorphins secretion was studied in 24 women with anorexia nervosa and 7 normal women. Serum LH, FSH, PRL, β-endorphin-like substance, ACTH, and cortisol concentrations were measured before and after opiate receptor blockade after a single iv dose of 0.2 mg/kg naloxone or saline. Mean serum LH and FSH concentrations increased significantly after naloxone in the normal women. Eleven patients had a significant increase in serum LH concentrations in response to naloxone and 13 did not respond to naloxone with an increase in LH concentration. In the first group the basal LH values were higher than those in the second group. In the majority of patients in the first group amenorrhea preceded the wt loss, whereas in most patients in the second group amenorrhea appeared during the phase of wt loss. Naloxone did not alter pulsatile LH secretion in 6 women. No effect of naloxone on serum FSH and PRL concentrations was found. A significant increase in β-endorphin-like substance levels after naloxone administration occurred in patients with anorexia nervosa. However, serum ACTH and cortisol concentrations were not altered in response to naloxone. In conclusion, the increase in LH release after opiate receptor blockade by naloxone suggests that endogenous opiates may play a role in the mechanism of inhibited LH secretion at least, in the majority of those women with anorexia nervosa in whom amenorrhea preceded wt loss. The results also point to a different mechanism of ACTH and j8-endorphin secretion in patients with anorexia nervosa.