Cortistatin-14 (CST-14) is an endogenous neuropeptide with notable structural similarities to native somatostatin-14 (SS-14), but different physiological functions. Differences in the physiology of the two peptides do not provide conclusive evidence for a specific receptor for CST. To date, the effects of CST-14 on anterior pituitary hormones have never been reported. Aim of this study was to investigate the in vivo effects of CST-14 on GH secretion in comparison to SS-14. Our results demonstrate that CST-14 was very effective in reducing GH secretion in normal male anaesthetized rats. Its activity was similar to that of SS-14 and had a rapid onset and a slightly longer duration of action. In conclusion, we have reported for the first time that CST is a potent and effective inhibitor of GH release in rats and that its action may be mediated by the interaction with one or different SS receptor subtypes.