Elevation of D-glucose impairs coronary artery autoregulation after slight reduction of coronary flow

Diabetes mellitus is thought to increase the susceptibility of tissue to hypoxic injury through D-glucose-induced alterations of intracellular metabolism. Therefore the effects of hyperglycaemia on coronary artery autoregulation under slight reduction of coronary flow were investigated in isolated perfused guinea-pig hearts. Under normal (10 mM) D-glucose concentrations coronary autoregulation was intact in response to a slight reduction of coronary flow (from 6 to 4.5 mL min-1) when L-arginine as a precursor of the endothelium-derived relaxing factor (EDRF/NO) was available and formation of prostaglandines was intact. Under high (44 mM) D-glucose concentrations on the other hand, a sustained vasodilatation dependent on the availability of L-arginine was observed, when formation of prostaglandins was blocked. This effect was partially reduced in the presence of prostaglandin synthesis. Furthermore, the effect of L-arginine under both conditions could be antagonized by the L-arginine-analogue NG-nitro-L-arginine-methyl-ester (100 microM). Our results suggest that hyperglycaemia impairs coronary artery autoregulation by reducing the threshold for hypoxic vasodilatation in an EDRF/NO-dependent manner. Concomitantly a shift from the formation of vasodilatatory to vasoconstrictive prostaglandines was observed. These results might be of particular interest in patients with diabetes mellitus and ischaemic heart disease.