Endothelial function and myogenic reactivity in small mesenteric arteries of hyperlipidemic pregnant rats

Supraphysiological increases in serum triglycerides and cholesterol often occur during pregnancy, but their effects on vascular function are poorly understood. Intraperitoneal injection of the nontoxic surfactant poloxamer 407 (P-407) results in sustained elevation of triglycerides and cholesterol. We asked if P-407-induced hyperlipidemia during late pregnancy adversely affects mesenteric resistance artery vasodilator function. On days 13-15 of pregnancy, rats were given a single intraperitoneal injection of P-407, sterile water vehicle, or non-lipid-altering pluronic F-88 (P-88). Four days postinjection, serum triglycerides, cholesterol, free fatty acids, and the lipid peroxidation product malondialdehyde were significantly increased in P-407-treated rats. Mesenteric arteries from P-407-treated rats displayed significant increases in myogenic reactivity (constrictor responses to step increases in intraluminal pressure). The nitric oxide (NO) blocker N(alpha)-methyl-L-arginine increased the myogenic response in control but not in P-407 arteries, normalizing group differences. Endothelial removal increased myogenic reactivity beyond that of prior NO synthase inhibition in controls and potentiated myogenic reactivity in P-407 arteries such that responses again converged. Relaxation responses to the endothelium-dependent vasodilator methacholine did not differ. We conclude that that P-407-induced hyperlipidemia during pregnancy increases myogenic reactivity due to selective attenuation of an NO-mediated vasodilator component of the myogenic response.