DAYTIME PLASMA MELATONIN LEVELS IN MALE HYPOGONADISM

It has previously been shown that increased nocturnal melatonin (MT) s ecretion exists in male patients with hypogonadotropic hypogonadism. H owever, little is known about the effects of gonadotropin and testoste rone (T) treatment on early morning plasma MT levels in male hypogonad ism. Also, the impact of gonadal steroids on plasma MT levels is an op en question. We, therefore, determined early morning plasma NPT levels at the same hour before and 3 months after treatment in 21 patients w ith idiopathic hypogonadotropic hypogonadism (IHH), 10 patients with p rimary hypogonadism, and 11 male controls. Plasma FSH, LH, PRL, T, and estradiol levels were also determined before and 3 months after treat ment. Patients with IHH were treated with hCG/human menopausal gonadot ropin, whereas patients with primary hypogonadism received T treatment . Short term treatments did not achieve normal T levels, although sign ificant increases in T were observed in both groups. Plasma MT levels were measured by a RIA with a sensitivity of 10.7 pmol/L. Mean plasma MT levels before treatment were significantly higher in MH (41.8 +/- 2 4.4 pmol/L) compared with those in the controls (21.7 +/- 10.8 pmol/L; P < 0.05). However, a slight, but not significant, increase in MT(34. 2 +/- 21.1 pmol/L) was found in primary hypogonadism. Mean MT levels d id not change significantly 3 months after the initiation of gonadotro pin (41.7 +/- 22.8 pmol/L) or T (28.4 +/- 12.6 pmol/L) treatment in ei ther IHH or primary hypogonadism, although a tendency for MT to decrea se was observed in both groups. No correlation was found between MT an d circulating FSH, LH, PRL, and gonadal steroids either before or afte r therapy. We conclude that male patients with IHH have increased earl y morning MT levels, although the pathophysiological mechanism is not clear. Furthermore, our study demonstrated that mean plasma MT levels are not influenced by short term gonadotropin or T treatment in male h ypogonadism, although a longer time effect of gonadotropins or T treat ment may not be excluded. The lack of correlation between plasma MT an d circulating gonadal steroids before and after treatment suggests tha t there is no classic feedback regulation between the pineal gland and the testes.