Effects of naloxone and coffee on anterior pituitary hormones

Both naloxone, a specific opiate antagonist, and caffeine and other components of coffee powders show influences on opiate receptors and on the secretion of some pituitary hormones. In order to study the possible effect of naloxone and coffee on the secretion pattern of hypophyseal hormones in man, experiments were performed in normal volunteers using either naloxone or coffee alone or both substances. Five healthy normal males, aged 25-30 years, received on three separate occasions and in random order: (i) coffee (4 cups of Italian style "espresso" coffee); or (ii) naloxone 12 micrograms/kg i.v.; or (iii) coffee plus naloxone simultaneously. The results show that naloxone given alone did not modify basal plasma PRL, GH, TSH, FSH or cortisol levels but significantly increased basal LH concentrations. On the other hand, the absorption of four cups of coffee did not modify the values of any of the hormones studied. The combination of the two drugs (coffee + naloxone) did not alter the response of the hormones studied to naloxone alone. It was concluded that coffee drinking, at least in these experimental conditions, does not appear to have any influence on anterior pituitary hormone secretion. Naloxone, on the other hand, is able to stimulate LH secretion even at very low doses.