ELEVATED BASAL ADRENOCORTICOTROPIN AND EVIDENCE FOR INCREASED CENTRALOPIOID TONE IN HIGHLY TRAINED MALE-ATHLETES

Basal cortisol and ACTH levels have previously been shown to be elevat ed in highly trained athletes, whereas the AGTH response to ovine CRH has been reported to be diminished compared to that in nonathletic con trols. Naloxone, a nonselective opioid receptor antagonist, is known t o stimulate ACTH and cortisol secretion. The mechanism of this respons e is thought to be via increased hypothalamic CRH secretion. The aim o f this study was to examine basal and naloxone-stimulated levels of hy pothalamic-pituitary-adrenal axis hormones in male athletes. Ten highl y trained male athletes and 10 nonathletic controls took part in the s tudy. Peripheral venous blood was sampled for cortisol, ACTH, CRH, and arginine vasopressin (AVP) for 2 h before the administration of 20 mg naloxone, iv, and 15, 30, 45, 60, 90, and 120 min after naloxone trea tment. Body mass index was significantly lower in the athletes (P < 0. 001). Basal (prenaloxone) ACTH levels were higher in the athletes (P < 0.05), whereas levels of cortisol, CRH, and AVP were similar in both groups. After naloxone treatment, there was a significantly greater ri se in ACTH in the athletes (P < 0.02). There was also a trend for the cortisol response to be greater, which was not statistically significa nt (P < 0.07). Although in both groups, peripheral CRH rose after nalo xone treatment (P < 0.005), a rise of similar magnitude occurred over the 2-h period before naloxone (P < 0.0001). Plasma AVP did not change significantly after naloxone treatment. Neither the plasma cortisol l evel at baseline nor the body mass index correlated significantly with the ACTH or cortisol response to naloxone. The presence of an enhance d ACTH response to naloxone is evidence that central opioid tone may b e increased in highly trained athletes. However, there is no associate d suppression of the hypothalamic-pituitary-adrenal axis, and basal AC TH levels are raised, without any detectable change in peripheral plas ma CRH or AVP. An additional factor (other than CRH) that stimulates A CTH secretion may be released after naloxone administration.