The differential effects of galanin-(1-30) and -(3-30) on anterior pituitary hormone secretion in vivo in humans

Intravenous injection of galanin increases plasma growth hormone (GH) and p rolactin (PRL) concentrations. In the rat, the effects of galanin on GH app ear to be mediated via the hypothalamic galanin receptor GAL-R-1, at which galanin-(3-29) is inactive. In contrast, the effect of galanin on PRL is me diated via the pituitary-specific galanin receptor GAL-R-W, at which galani n-(3-29) is fully active. We investigated the effects of an intravenous inf usion of human galanin (hGAL)-(1-30) and -(3-30) on anterior pituitary horm one levels in healthy females. Subjects were infused with saline, hGAL-(1-3 0) (80 pmol . kg(-1) . min(-1)), and hGAL-(3-30) (600 pmol . kg(-1) . min(- 1)) and with boluses of gonadotropin-releasing hormone, thyrotropin-releasi ng hormone, and growth hormone-releasing hormone (GHRH). Both hGAL-(1-30) a nd -(3-30) potentiated the rise in GHRH-stimulated GH levels [area under th e curve (AUC), saline, 2,810 +/- 500 vs. hGAL-(1-30), 4,660 +/- 737, P < 0. 01; vs. hGAL-(3-30), 6,870 +/- 1,550 ng . min . ml(-1), P < 0.01]. In contr ast to hGAL-(1-30), hGAL-(3-30) had no effect on basal GH levels (AUC, sali ne, -110 +/- 88 vs. hGAL1-30, 960 +/- 280, P < 0.002; vs. hGAL-(3-30), 110 +/- 54 ng . min . ml(-1), P = not significant). These data suggest that the effects of galanin on basal and stimulated GH release are mediated via dif ferent receptor subtypes and that the human equivalent of GAL-R-W may exist .