MELATONIN CONCENTRATION BEFORE AND DURING TESTOSTERONE REPLACEMENT INPRIMARY HYPOGONADIC MEN

Objective: To study circadian levels of melatonin in primary hypogonad ic adult men before and after testosterone treatment, Design and metho ds: Circadian serum melatonin profiles were studied in sh men with pri mary hypogonadism before and during testosterone substitution and comp ared with an age-matched control group (n=6). Results: Hypogonadal pat ients had higher plasma melatonin concentrations than the control grou p during day time (34.2+/-8.8 compared with 5.4+/-0.5 ng/l, means+/-S. D.; P<0.005) and night-time (74.8+/-34.5 compared with 30.8+/-3.2 ng/l ). A 3 months course of testosterone replacement treatment in the hypo gonadal group was followed by a diminution of the amplified melatonin circadian rhythm, with lower mean values both during the day (34.2.8+/ -8 compared with 12.7+/-2.45 ng/l. P<0.001) and at night (74.8+/-34.5 compared with 41.5+/-13.5 ng/l, P<0.01), and a decrease in the total a rea tinder the curve (958+/-318 compared with 475.5+/-222.9, P=0.046). There was a significant negative correlation between melatonin (r=-0. 69) and testosterone concentrations. Conclusions: These data indicate that diminished testosterone in male primary hypogonadism is associate d with enhanced plasma levels of melatonin, and that testosterone subs titution treatment induces a deamplification of the circadian rhythm o f melatonin values in humans.