POTENTIATING EFFECT OF GALANIN ON GHRH-INDUCED GH RELEASE - COMPARISON BETWEEN OLD AND YOUNG SUBJECTS

The aim of our study was to investigate the effect of galanin on basal and GHRH-stimulated GH secretion in a healthy group of elderly subjec ts and in a healthy group of young subjects for comparison. Ten old su bjects (mean age 75 +/- 1.15 years) and an equal number of healthy you ng volunteers (mean age 26 +/- 0.71 years) underwent three stimulation tests in random order. Galanin infusion for 60 minutes (10 mu g/kg in 100 mi saline) failed to provoke an appreciable release of circulatin g GH in old subjects, while it induced a significant increase of plasm a CH in the young adults; GHRH administration i.v. in bolus (100 mu g in 1 ml saline) elicited a significant CH response in both groups; how ever, in the older group GH response was significantly (p < 0.05) lowe r than in the young adults. The administration of galanin (10 mu g/kg in 100 ml saline as an i.v. infusion for 60 min) plus GHRH (100 mu g i n 1 ml saline i.v. in bolus), potentiated GH response in old and young subjects. The combined administration of two peptides was able to eli cit a clear GH release even in the older subjects who were hyporespons ive/unresponsive to galanin and/or GHRH alone. In the elderly, plasma GH values observed after the combined stimuli overlapped with GH value s observed after GHRH alone in the young adults. In conclusion, our st udy confirms that galanin has a synergic effect with GHRH on GH releas e both in younger and elderly subjects. Moreover, our data confirm an impaired responsivity to GHRH in the elderly and demonstrate that gala nin is able to normalize response of somatotrophs to GHRH in old peopl e.