COMPARISON OF CUMULATIVE AND NON-CUMULATIVE ADMINISTRATION OF VASOACTIVE AGENTS IN ARTERIAL SMOOTH-MUSCLE RESPONSES IN-VITRO

Two methods of determining concentration-response curves were compared in isolated endothelium-intact mesenteric arterial rings from Wistar rats: arterial contractile and relaxation responses were elicited by a dding compounds cumulatively or introducing a single concentration at a time (non-cumulative method). The contractile responses induced by h igh concentrations of K+ (20-125 mM) were comparable between the two m ethods, whether or not the responses were elicited in the presence of phentolamine (10 muM) and atenolol (10 muM). Noradrenaline (1 nM - 10 muM) likewise induced similar contractions regardless of method of adm inistration, the only exception being the highest concentration (100 m uM) which produced lower contractile force when added directly upon re sting tension than after cumulative administration. This difference wa s abolished by atenolol (10 muM). Arterial smooth muscle relaxations i nduced by endothelium-dependent (acetylcholine 1 nM - 10 muM) and -ind ependent agents (nitroprusside 1 nM - 1 muM, isoprenaline 10 nM - 100 muM) were similar whether the relaxants were added in a cumulative fas hion or in a single concentration introduced upon each precontraction. Thus, cumulative and non-cumulative administration of contractile and relaxing agents give quite comparable results. We conclude that the c umulative method is a reliable and time-saving way of studying vascula r smooth muscle responses in vitro.