Effect of the combined administration of galanin and clonidine on serum growth hormone levels in normal subjects and in patients under chronic glucocorticoid treatment.

Abstract

Aim of our study was to investigate the effect of clonidine and galanin (alone or in combination) on growth hormone (GH) secretion in normal subjects and in adult patients with increased somatostatin tone due to chronic daily immunosuppressive glucocorticoid treatment. We studied 7 adult patients undergoing long-term (no less than 6 months) immunosuppressive glucocorticoid treatment for non endocrine diseases (4F, 3M; age 49.7 +/- 6.3 years). Six normal adult nonobese subjects (3F, 3M; age 34 +/- 2.7 years) served as controls. All subjects underwent the following three tests in random order: 1) iv infusion of clonidine, 150 micrograms in 10 mL of saline, from time 0 to 10 min; 2) iv infusion of synthetic porcine galanin, 500 micrograms in 100 mL of saline from -15 to 30 min; 3) iv infusion of clonidine from 0 to 10 min combined with synthetic porcine galanin iv infusion from -15 to 30 min. Blood samples for GH assay were taken at -15, 0, 15, 30, 45, 60, 90, 120 min. No significant differences in GH absolute values were observed at any time between the three different tests within each group of subjects. Normal subjects showed significantly (p < 0.05) higher GH peaks and GH absolute values from 15 to 90 min after galanin alone, clonidine alone and clonidine+galanin with respect to the glucocorticoid-treated patients. The absence of any either synergistic or at least additive effect on GH secretion of galanin and clonidine in conditions of both normal and increased somatostatin tone suggests that also in man, as well as in the rat, the action of galanin on the GH axis may be mediated through alpha-adrenergic pathways.