MINIMAL EFFECTS OF NITRIC-OXIDE ON SPATIAL BLOOD-FLOW HETEROGENEITY OF THE DOG HEART

Eleven Beagle dogs were studied to elucidate the possible role of L-ar ginine-derived nitric oxide on local blood flow distribution in left a nd right ventricular myocardium. Local blood flow was determined in 25 6 samples from the left and 64 samples from the right ventricle per he art using the tracer microsphere technique (mean sample mass 319 +/- 1 31 mg). Nitric oxide production was effectively inhibited by intraveno us infusion of 20 mg/kg nitro-l-arginine methylester (L-NAME) as evide nced by a shift of the dose/response curve for the effect of intracoro nary administration of bradykinin (0.004-4.0 nmol/min) on coronary blo od flow. L-NAME enhanced left and right ventricular systolic pressures from 132 +/- 18 to 155 +/- 15 mm Hg and from 26 +/- 3 to 29 +/- 3 mm Hg respectively (both P = 0.043). Mean left ventricular blood flow was 1.14 +/- 0.38 before and 0.99 +/-:0.28 mi min(-1) g(-1) after L-NAME (P = 0.068), while right ventricular blood flow fell from 0.72 +/- 0.2 8 to 0.53 +/- 0.20 mi min(-1) g(-1) (P = 0.043). Coronary conductance of left and right Ventricular myocardium fell by 31 and 43% respective ly (both P = 0.043). The coefficient of variation of left ventricular blood flow was 0.26 +/- 0.07 before and 0.29 +/- 0.07 after L-NAME (P = 0.068), that of right ventricular blood flow was 0.27 before and aft er L-NAME. Skewness (0.51) and kurtosis (4.23) of left ventricular blo od flow distribution were unchanged after L-NAME, while in the right v entricle skewness decreased from 0.54 to 0.09 (P = 0.043) and kurtosis (3.68) tended to decrease after L-NAME (P = 0.080). The fractal dimen sion (D = 1.20-1.27) and the corresponding nearest-neighbor correlatio n coefficient (r(n) = 0.37-0.53) of left and right ventricular myocard ium remained unchanged after infusion of L-NAME. From these results it is concluded that firstly, local nitric oxide release does not explai n the higher perfusion of physiological high flow samples and secondly , that spatial myocardial blood flow coordination is not dependent on nitric oxide.