Effects of sex and age on the growth hormone response to galanin in healthy human subjects.

The aim of our study was to analyze the effects of sex and age on the GH response to galanin infusion in healthy subjects. We have studied 12 young (age, < 40 yr) nonobese healthy volunteers [6 females: age, 31.0 +/- 2.5 yr; body mass index (BMI), 21.6 +/- 0.9 kg/m2; 6 males: age, 29.2 +/- 1.4 yr; BMI, 23.3 +/- 0.4 kg/m2] and 11 old (age, > 65 yr) healthy subjects (5 females: age, 83.8 +/- 3.8 yr; BMI, 23.4 +/- 1.4 kg/m2; 6 males: age, 79.7 +/- 4.6 yr; BMI, 23.3 +/- 0.2 kg/m2). All subjects received an infusion of synthetic porcine galanin (500 micrograms, iv) in 100 mL saline from 0-45 min. Blood samples for GH measurement were drawn at -15, 0, 15, 30, 45, 60, 90, and 120 min. The GH peaks after galanin treatment in young females (11.9 +/- 2.9 micrograms/L) were significantly (P < 0.05) higher than those in the young males (5.1 +/- 1.8 micrograms/L). Old males showed significantly higher peak GH levels after galanin treatment (8.6 +/- 3.1 micrograms/L) than old females (2.4 +/- 0.6 micrograms/L). The GH peaks and areas under the curve after galanin treatment were significantly (P < 0.05) higher in young than in old females. On the contrary, no significant differences were observed after galanin treatment in young and old males. The magnitude of galanin-induced GH secretion significantly correlated with estradiol levels in young women. Our data seem to suggest that circulating estrogen levels play a crucial permissive role in galanin-induced GH secretion in humans.