CIRCADIAN AND ULTRADIAN VARIATIONS OF PITUITARY AND PINEAL HORMONES IN NORMAL MEN - EVIDENCE FOR A LINK BETWEEN MELATONIN, GONADOTROPIN, AND PROLACTIN SECRETION

The study was performed to investigate the physiological relationship between the pineal hormone melatonin and pituitary functions in normal men. Series of blood samples were obtained at 10-min intervals for 24 -hr periods from 10 male volunteers (age 19-25 years). Samplings were repeated after 2 weeks and 3 months. Serum levels of melatonin, follic le-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL ), and testosterone (T) were estimated by immunoassay methods (LH, PRL , every sample; melatonin, every 30 min; T, every 4 hrs; FSH once for each session). Diurnal characteristics of PRL and melatonin profiles w ere estimated by complex cosinor analysis, while short-term pulsatilit y of LH and PRL secretion was analyzed by the PULSAR algorithm. Data w ere correlated by linear regression analysis. The combined information of all three sampling sessions revealed significant negative correlat ions between the following parameters (N = 10): Amplitude (Ampl) melat onin and Ampl PRL: r = -0.727, P < 0.02; Ampl melatonin and maximal (M ax) PRL values: r = -0.73, P < 0.02; Max melatonin and Max PRL: r = -0 .725, P < 0.02; area under the curve (AUG) melatonin and Ampl PRL: r = -0.637, P < 0.05; AUC melatonin and Max PRL: r = -0.640; P < 0.05; du ration (Dur) of melatonin synthesis and Ampl PRL: r = -0.685, P < 0.03 ; Dur melatonin and Max PRL: r = -0.676, P < 0.04; Dur melatonin and F SH levels: r = -0.663, P < 0.04; AUC melatonin and LH mean concentrati on: r = -0.732, P < 0.02; Max melatonin and LH mean concentration: r = -0.657, P < 0.04. These correlations varied considerably between the three sessions, mainly due to intra-individual variabilities of secret ory patterns of PRL and LH, while the melatonin profiles were comparab ly stable. The results indicate that melatonin production and pituitar y functions may be related in normal men. Because of the substantial i ntra- and inter-individual variations in hormone secretory patterns, l arge numbers of volunteers and/or repeated measurements are essential for studies addressing the pineal-pituitary connection in normal human s.