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 subjects and in a healthy group of young subjects for comparison. Ten old subjects (mean age 75 +/- 1.15 years) and an equal number of healthy young volunteers (mean age 26 +/- 0.71 years) underwent three stimulation tests in random order. Galanin infusion for 60 minutes (10 micrograms/kg in 100 ml saline) failed to provoke an appreciable release of circulating GH in old subjects, while it induced a significant increase of plasma GH in the young adults; GHRH administration i.v. in bolus (100 micrograms in 1 ml saline) elicited a significant GH response in both groups; however, in the older group GH response was significantly (p < 0.05) lower than in the young adults. The administration of galanin (10 micrograms/kg in 100 ml saline as an i.v. infusion for 60 min) plus GHRH (100 micrograms in 1 ml saline i.v. in bolus), potentiated GH response in old and young subjects. The combined administration of two peptides was able to elicit a clear GH release even in the older subjects who were hyporesponsive/unresponsive to galanin and/or GHRH alone. In the elderly, plasma GH values observed after the combined stimuli overlapped with GH values observed after GHRH alone in the young adults. In conclusion, our study confirms that galanin has a synergic effect with GHRH on GH release both in younger and elderly subjects. Moreover, our data confirm an impaired responsivity to GHRH in the elderly and demonstrate that galanin is able to normalize response of somatotrophs to GHRH in old people.