EFFECTS OF CARDIAC SYMPATHETIC-NERVE STIMULATION ON THE LEFT-VENTRICULAR END-SYSTOLIC PRESSURE-VOLUME RELATIONSHIP AND PLASMA NOREPINEPHRINE DYNAMICS IN DOGS

The effects of cardiac sympathetic nerve (CSN) stimulation on the left ventricular end-systolic pressure-volume relationship (ESPVR) and pla sma norepinephrine (NE) concentration in arterial blood were studied i n dogs. In 12 anesthetized and open-chest dogs, left ventricular press ure and volume were measured simultaneously with a microtip catheter a nd a conductance catheter, respectively. The ESPVR values were constru cted from pressure-volume loops during a brief occlusion of the inferi or vena cava before and after a 40-sec train of electrical CSN stimula tion. The slope (E-max) of the ESPVR line was significantly greater af ter CSN stimulation than before CSN stimulation (p < 0.05) for both ri ght and left CSN stimulation. The increased E-max values after right a nd left CSN stimulation were not significantly different from each oth er. In 5 dogs, time courses of E-max, left ventricular systolic pressu re, heart rate, and plasma NE concentration after CSN stimulation were studied. Left ventricular systolic pressure and heart rate returned t o the baseline more rapidly than E-max and arterial plasma NE concentr ation. There was a positive, linear correlation between E-max(y) and a rterial plasma NE concentration (x), shown as y 3.3 X 10(-3)X + 3.1 (n = 30, r = 0.86, p < 0.05). These results imply that cardiac contracti le enhancement is reflected in arterial plasma NE concentration in con ditions in which CSN is activated.