Inhibition of cyclic AMP- and cyclic GMP-mediated dilations in isolated arteries by oxidized low density lipoproteins.

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Abstract
We studied the effects of native (N) and oxidized (Ox) low density lipoproteins (LDLs) on adenosine 3',5'-cyclic monophosphate (cAMP)-mediated and on guanosine 3',5'-cyclic monophosphate (cGMP)-mediated dilator mechanisms in isolated, perfused human mammary and rabbit femoral arteries. Dilations were induced in preconstricted, deendothelialized segments by either forskolin (Fo) or sodium nitroprusside (SNP) (intraluminal or adventitial application). Lipoproteins (0.5 mg/ml) were administered to the segments from the intraluminal side. N-LDL had no effect on Fo-induced dilation and caused a weak attenuation of SNP-induced dilation only when SNP was also administered into the intraluminal perfusate. In contrast, Ox-LDL inhibited both Fo- and SNP-induced dilation, independent of the route of dilator application. The effects of Ox-LDL were specific for dilation mediated by cyclic nucleotides. Dilation elicited by the Ca2+ antagonist nitrendipine was inhibited neither by N-LDL nor by Ox-LDL. Determination of basal and stimulated (SNP, Fo) cGMP and cAMP content in rabbit femoral segments after preincubation with N-LDL and Ox-LDL revealed a significant decrease of stimulated vascular cGMP and cAMP content by Ox-LDL, whereas N-LDL had no effect. These data indicate that Ox-LDL selectively inhibits vascular smooth muscle relaxation elicited by increases in cyclic nucleotides. This inhibition might contribute to the attenuation of vasodilation in hypercholesterolemia and atherosclerosis.

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