Roles of calcium and arachidonic acid metabolism in endothelium-dependent dilatation of coronary arteries

j Mol Cell Cardiol 18 (Supplement 1) (1986) 1 9 5 1 N S U L I N INHIBITS C O E N Z Y ~ A DEGRADATION IN THE DIABETIC RAT HEART. G.D. Lopaschuk and J.R. Neely, Dept. of Physiology, Hershey Medical Center, Hershey, PA, USA Coenzyme A(CoA) degradation was studied in isolated working hearts from acutely diabetic rats (48 hr). Hearts from diabetic rats had elevated levels o f CoA (752 + 15 nmol/g dry) compared to control hearts (537 + 14 nmol/g dry. If diabetic hearts were perfused for 5 minutes with 5 m M pyruvate no change in CoA levels was observed (final CoA concentration was 735 + 17 nmol/g dry). Perfusion with 1.2 ram palmitate resulted in a rapid drop in CoA levels to 672 + 19 nmol/g dry. A similar perfusion condition in control hearts had no effect on CoA levels. Addition of insulin (25 mU/ ml) to the buffer prevented the decrease in CoA levels fr~n occurring in diabetic hearts perfused with palmitate (final CoA content was 743 + 36 nmol/g dry). The level of long chain acyl CoA in diabetic hearts perfused w~th pyruvate was 105 + ll without and 117 + 14 nmol/g dry with insulin present. Perfusion of diabetic hearts with palmitate r~sulted in an increase in tb~ levels of long chain acyl CoA from 76 _+ 16 to 149 + 13 nmol/g dry. A similar effect of fatty acids to increase acyl CoA levels and accelerate CoA degradation was observed in hearts whose whole tissue CoA levels were increased by in vitro perfusion with no exogenous energy substrate. If insulin was present in the perfusate of diabetic hearts long chain acyl CoA levels increased further s 192 + 18 rm~i/g dry. These data indicate that rapid degradation of CoA can occur in-the dYabetio myocardi~n, and is inhibited by insulin. This degradative pathway may metabolize long chain acyl CoA. S~oported by HL13028.

196ROLES

OF CALCIUM AND ARACHIDONIC ACID METABOLISM IN ENDOTNELIUM-DEPENDENT DILATATION OF CORONARY ARTERIES. P.S. MacDonald, G.J. Dusting, Department of Physiology, University of Melbourne, Parkville, Victoria 3052.

The release of endothelium-derived relaxing factor (EDRF) induced by acetylcholine and the calcium ionophore (A23187) has been previously found to depend on entry of extraeellular calcium ion. We have studied endothelium-dependent relaxation of bovine coronary artery rings precontracted with the thromboxane-mlmetic U46619. Arachidonic acid (0.01-I00 pM) produced concentration-dependent relaxation of these rings that was endothelium'dependent and was identical in normal Krebs solution (2.5 mM Ca 2+) and in calcium-free solution. The marked relaxation produced by A23187 (0.i-i ~M) in normal Krebs solution was abolished in calcium-free solution. Since this suggested that arachidonic acid could be bypassing an initial calcium dependent step in release of EDRF, we studied the effect of inhibitors of arachidonate metabolism in calciumfree solution. Relaxation produced by arachidonic acid was not altered by indomethacin (3 ~M) but was abolished by SKF-525A (I raM). Relaxation induced by glyceryl trinitrate is not dependent on the presence of endothelium and was not inhibited by SKF-525A. It is suggested that arachidonic acid could be acting as a precursor of an EDRF, and the data is consistent with a cytochrome P-450 mono-oxygenase pathway being involved in synthesis or release of EDRF.

197

XANTHINE CKIDASE-I)ER~"~)FREE RADICAI~. A.S. Manning, The Rayne Institute, St Thomas' hbspital, London SEI, U.K. We have suggested previously that oxygen-derived free radicals produced by xanthine oxidase may be an important trigger mechani~n for the genesis of reperfusion-ir~uoed arrhyt~mLias. We have further assessed this theory by (i)ex~anining in an ~aesthetized rat preparation the effects of xanthine (x(idase inhibitors, folic acid solution and soybean trypsin inhibitor and (ii) in an isolated rat heart preparation investigating the ability of the. free radical generating systen, xanthine oxidase a n d hypoxanthine, to increase reperfusion-induced arrhytbmias and then studying whether the addition of free radical scavengers can reduce this. Administrationof folic acid solution (10mg/kg orally 24h prior to experimentation and 10mg/kg i.v. 10 ~Rn prior to coronary artery occlusion - CAO) significantly reduced the incidence of reperfusion-inducedventric~lar fibrillation (RVF) after a 5 rain period of CAO from 67% to 17% (P 0.02). The incidenoes of reperfusion ventricular tachycardia (R~T) and mortality were similarly reduced. Administrationof soybean trypsin inhibitor (4mg/kg i.p., 4h prior to experimentation) also reduced significantlythe ineider~e of RVF, RVT and mortality. In an isolated perfused rat heart preparation (n=15 in each group), addition of 10 uM hypoxanthine and 1 unit/litre xanthine oxidase, increased the ir~idence of RVF and ]~T. Further addition of the 02"scavenger, anparoxide dismutase (0.1 unit/litre) reduned the incidence of reperfusion-indueed Ventricular arrhythmias caused by the addition of xanthine oxidase/hypoxanthine, and increased the total duration of normal sinus rhythm. We suggest this is evidence s~pporting a role for free radicals produced by x~nthine oxidase in the genesis of reperfusion-inducedarrhythmias. R~I~SION-INDUEED A ~ A ~ M I A S : A POSSIBLE I~0LE ~