Effect of nicotine on in vivo secretion of melanocorticotropic hormones in the rat

Corticosterone, ACTH, β-endorphin and α-MSH were measured in rat plasma by radioimmunoassay before and 2,5,15,30 minutes after an intraperitoneal injection of nicotine (500 μg/Kg b.w.). Nicotine induced an increase of plasma corticosterone (p < 0.05 at t + 15 min), ACTH and β-endorphin (p < 0.01 at t + 5 min) and a decrease of α-MSH (p < 0.005 at t + 15 min). Dose response experiments showed an increase of corticosterone, ACTH, β-endorphin 15 min after 250 μg/Kg b.w. nicotine I.P., no effect being observed after injection of 100 μg/Kg b.w. The decrease of α-MSH was observed 15 min after 100, 250 or 500 μg/Kg b.w. nicotine I.P. Our results suggest that the increase of corticosterone is mediated through ACTH release.