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, follicle-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 were estimated by complex cosinor analysis, while short-term pulsatility of LH and PRL secretion was analyzed by the PULSAR algorithm. Data were correlated by linear regression analysis. The combined information of all three sampling sessions revealed significant negative correlations between the following parameters (N = 10): Amplitude (Ampl) melatonin and Ampl PRL: r = -0.727, P < 0.02; Ampl melatonin and maximal (Max) 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; duration (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 FSH levels: r = -0.663, P < 0.04; AUC melatonin and LH mean concentration: 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 secretory patterns of PRL and LH, while the melatonin profiles were comparably stable. The results indicate that melatonin production and pituitary functions may be related in normal men. Because of the substantial intra- and inter-individual variations in hormone secretory patterns, large numbers of volunteers and/or repeated measurements are essential for studies addressing the pineal-pituitary connection in normal humans.