Dose-response curve showing the relaxation elicited by guanidinosuccinic acid in the rat aorta preparation. The NO-synthase inhibitor L-NMMA reverses the effect of guanidinosuccinic acid in the rat aorta. GSA, guanidinosuccinic acid. L-NMMA, N-monomethyl-L-arginine. (Modified and reprinted with permission from Thomas and Ramwell.62)