INTERACTION OF SALBUTAMOL AND GALANIN ON BOTH BASAL AND GROWTH-HORMONE RELEASING HORMONE-STIMULATED GROWTH-HORMONE SECRETION IN HUMANS

Beta adrenergic receptors mediate the inhibitory influence of catecholamines on GH secretion in man, likely via stimulation of hypothalamic somatostatin release. To further clarify the role of beta adrenergic receptors in the neural control of GH secretion, in 7 normal females (age 21-27 yr) we studied the interaction of salbutamol (SAL 0.08 mg/kg orally), a beta 2-adrenergic agonist, with GHRH (1 mu g/kg iv) and/or galanin (GAL 15 mu g/kg iv), a neuropeptide endowed with a GH-releasing effect which is likely mediated by concomitant stimulation of GHRH- and inhibition of somatostatin-secreting neurons. SAL inhibited the GH response to GHRH (AUC: 282.6 +/- 102.7 vs 1083.6 +/- 176.5 mu g/l/h, p< 0.05) and, although not significantly, that to GAL (263.9 +/- 103.7 vs 418.4 +/- 70.4 mu g/l/h). GAL enhanced the GHRH-induced GH rise (2129.5 +/- 362.2 mu g/l/h, p< 0.05) but SAL pretreatment inhibited this effect (1249.8 +/- 257.1 mu g/l/h, p< 0.02) so that the GH response to the combined administration of GHRH, GAL and SAL overlapped with that to the neurohormone alone. In conclusion, our results show that the inhibitory influence of beta adrenergic activation on GH secretion overrides the stimulatory one of galanin. They strenghten the view that in man beta-adrenergic receptors and galanin modulate GH secretion having opposite influences aimed to balance the function of the GH-IGF-I axis.