NOCTURNAL MELATONIN AND LUTEINIZING-HORMONE RHYTHMS IN WOMEN WITH HYPERPROLACTINEMIC AMENORRHEA

To examine the role of melatonin in pathological hyperprolactinemia we compared untreated young females (N = 5) with hyperprolactinemic amen orrhea owing to pituitary microadenoma to healthy female controls (N = 6). Serum samples for melatonin, prolactin, and luteinizing hormone ( LH) concentrations were obtained every 15 min from 1900 hr to 0700 hr in a controlled light-dark environment with simultaneous sleep recordi ngs. The mean (+/- SD) light-time period, dark-time period, and the in tegrated nocturnal melatonin secretion values (area under the curve, o r AUG) in patients (51 +/- 11 pmol/L, 157 +/- 33 pmol/L, and 102 +/- 1 9 pmol/min . L x 10(3), respectively) were similar to the values obtai ned in controls (79 +/- 39, 165 +/- 44, 111 +/- 31, respectively). The onset of the nocturnal melatonin rise, peak level, and peak time were similar in the two groups. A significant nocturnal prolactin rise was observed in patients (112 +/- 9 vs. 65 +/- 11 mu g/L, P < 0.006) and controls (19 +/- 2 vs. 10 +/- 3 mu g/L, P < 0.006). The time of prolac tin peak was similar in patients and controls (0424 +/- 3:35 vs. 0350 +/- 2:21) and paralleled that of melatonin (0354 +/- 1:46 vs. 0337 +/- 1:30). The mean +/- SD light-time period, dark-time period, and the A UC values of LH were similar in patients and controls. The number of L H pulses in patients (7.2 +/- 1.9 per 12 hr) were not different from t hose in controls (7.7 +/- 2.1). The LH pulse interval was 100 +/- 22 m in in patients compared with 94 +/- 23 min in controls. The mean (+/- SD) nocturnal estradiol (E2) levels were significantly lower in patien ts (84 +/- 15 pmol/L) than in controls (224 +/- 77) (P < 0.005). Analy sis of LH and melatonin secretory profiles revealed significant pulses for both hormones. No significant relationship was observed between t he LH and melatonin pulses. However, a negative correlation between LH pulse amplitude and the number of melatonin pulses (P < 0.04) and a p ositive correlation between LH amplitude and duration of melatonin pul ses (P < 0.04) were observed. Taken together, these data suggest that the suppression of normal ovarian cycles in women with hyperprolactine mic amenorrhea owing to pituitary microadenoma may be mediated by bloc king of gonadotropin action by prolactin at the ovarian level; yet it remains possible that chronically elevated prolactin might prevent the LH surge and thus lead to amenorrhea. Pulsatile melatonin secretion i s unaltered in these patients, and the frequent occurrence of amenorrh ea in this population is not mediated by melatonin.