PHYSIOLOGICAL-ROLE OF GALANIN IN THE REGULATION OF ANTERIOR-PITUITARY FUNCTION IN HUMANS

The aim of our study was to elucidate the physiological role of the neuropeptide galanin in the regulation of anterior pituitary function in human subjects. Six healthy men (age range 26-35 yr, body mass index range 20-24 kg/m(2)) underwent in random order 1) an intravenous bolus injection of growth hormone-releasing hormone (GHRH)-(1-29)-NH2 (100 mu g) + thyrotropin-releasing hormone (TRH, 200 mu g) + luteinizing hormone-releasing hormone (LHRH, 100 mu g) + corticotropin-releasing hormone (CRH, 100 mu g), and 2) intravenous saline (100 ml) at time 0 plus either human galanin (500 mu g) in saline (100 mo or saline (100 mi) from -15 to +30 min. Human galanin determined a significant increase in serum GH (GH peak: 11.3 +/- 2.2 mu g/l) from both baseline and placebo levels. No significant differences were observed between GH values after galanin and those after GHRH alone (24.3 +/- 5.2 mu g/l). Human galanin significantly enhanced the GH response to GHRH (peak 49.5 +/- 10 mu g/l) with respect to either GHRH or galanin alone. Human galanin caused a slight decrease in baseline serum adrenocorticotropic hormone (ACTH; 16.3 +/- 2.4 pg/ml) and cortisol levels (8 +/- 1.5 mu g/dl). Galanin also determined a slight reduction in both the ACTH (peak 27 +/- 8 pg/ml) and cortisol (peak 13.8 +/- 1.3 mu g/dl) responses to CRH. Baseline and releasing hormone-stimulated secretions of prolactin, thyroid-stimulating hormone, LK, and follicle-stimulating hormone were not altered by galanin. Our data suggest a physiological role for the neuropeptide galanin in the regulation of GH secretion in humans. A minor inhibitory role seems to be played by galanin in regulating ACTH and cortisol levels.