Melatonin concentration before and during testosterone replacement in primary hypogonadic men

Objective: To study circadian levels of melatonin in primary hypogonadic adult men before and after testosterone treatment. Design and methods: Circadian serum melatonin profiles were studied in six men with primary hypogonadism before and during testosterone substitution and compared with an age-matched control group (n=6). Results: Hypogonadal patients had higher plasma melatonin concentrations than the control group 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 hypogonadal 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 area under 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 associated with enhanced plasma levels of melatonin, and that testosterone substitution treatment induces a deamplification of the circadian rhythm of melatonin values in humans.