Intracerebroventricular growth-hormone-releasing peptide-6 stimulates eating without affecting plasma growth hormone responses in rats

The purpose of this study was to determine the effect of intracerebroventricular (icv) injections of a synthetic, opioid-related hexapeptide, growth-hormone-releasing peptide-6 (GHRP-6), on stimulation of eating by rats and to correlate this aspect of feeding behavior with the peripheral plasma growth hormone (GH) response to the administered peptide. GHRP-6 dissolved in 5 μL of saline was injected into the lateral ventricles of sated, adult, male, Sprague-Dawley rats in doses from 0 pmol (saline only) to 1000 pmol. For 1 hour after injection, the occurrence of eating was noted, and specimens of arterial blood were collected at 0, 15, 30, and 60 minutes. The plasma was assayed for GH. A nearly linear, statistically significant (p < 0.01) dose-response relationship between the dose of GHRP-6 and the incidence of eating was noted. The mean change from baseline of plasma GH during the 60 minutes after injection was not dose-related (p > 0.2, p > 0.1, and p > 0.1 at 15, 30, and 60 minutes, respectively). We conclude that GHRP-6 given intracerebroventricularly to sated, adult, male, Sprague-Dawley rats stimulates eating and suggest that it does so by some mechanism that is independent of its GH-releasing property.