PHARMACOLOGICAL STUDIES ON THE MECHANISM OF MELATONIN-INDUCED VASORELAXATION IN RAT AORTA

The influence of several classes of drugs on the melatonin-induced vas orelaxation of isolated rat aorta were examined. Melatonin caused a do se-dependent relaxation of precontracted (30 mM KCl) aorta. This relax ant response was blocked by preincubating vessels with antagonists of vasoactive intestinal peptide. Substance P antagonists did not alter t he response to melatonin. Pretreatment of vessels with 6-hydroxydopami ne, Iidocaine, or tetrodotoxin antagonized the relaxant response to me latonin. On the other hand, pretreatment with atropine + propranolol d id not alter the response to melatonin. These experiments suggest that melatonin may exert part of its vasoactive actions by an interaction with perivascular nerve terminals.