Flow-induced constriction in arterioles of hyperhomocysteinemic rats is due to impaired nitric oxide and enhanced thromboxane A(2) mediation

Hyperhomocysteinemia (HHcy) is thought to promote arteriosclerosis and peri pheral arterial disease, in part by impairing the function of endothelium. Because flow-induced dilation is mediated by the endothelium, we hypothesiz ed that HHcy alters this response by interfering with the synthesis/action of NO and prostaglandins. Thus, changes in the diameter of isolated, pressu rized (at 80 mm Hg) gracilis skeletal muscle arterioles (diameter approxima te to 170 mum) from control and methionine diet-induced HHcy rats were inve stigated with videomicroscopy. Increases in intraluminal flow (from 0 to 25 muL/min) resulted in dilations of control arterioles (maximum, 34 +/-4 mum ). In contrast, increases in flow elicited constrictions of HHcy arterioles (-36 +/-3 mum). In control arterioles, the NO synthase inhibitor N-omega-n itro-L-arginine-methyl ester significantly attenuated (approximate to 50%) dilation, whereas the additional administration of indomethacin, an inhibit or of cyclooxygenase, eliminated flow-induced dilation. In the arterioles o f III-icy rats, flow-induced constriction was not affected by N-omega-nitro -L-arginine-methyl ester, whereas it was abolished by indomethacin or the p rostaglandin H-2/thromboxane A(2) (TXA(2)) receptor antagonist SQ 29,548 or the TXA(2) synthase inhibitor CGS 13,080. Thus, in HHcy, increases in intr aluminal flow elicit constrictions of skeletal muscle arterioles due to the impaired NO and enhanced TXA(2) mediation of the response, alterations tha t likely contribute to the development of peripheral arterial disease.