15-Lipoxygenase metabolites contribute to age-related reduction in acetylcholine-induced hypotension in rabbits

Arachidonic acid (AA) metabolites from the 15-1ipoxygenase-1 (15-LO-1) pathway, trihydroxyeicosatrienoic acids (THETAs) and hydroxy-epoxyeicosatrienoic acids (HEETAs), are endothelium-derived hyperpolarizing factors (EDHFs) and relax rabbit arteries. Rabbit vascular 15-LO-1 expression, THETA and HEETA synthesis, and nitric oxide and prostaglandin-independent relaxations to acetylcholine (ACh) and AA decreased with age (neonates to 16-wk-old). We characterized age-dependent ACh-hypotensive responses in vivo in 1-, 4-, 8-, and 16-wk-old rabbits and the contribution of THETAs and HEETAs to these responses. In anesthetized rabbits, blood pressure responses to ACh (4-4,000 ng/kg) were determined in the presence of vehicle or various inhibitors. ACh responses decreased with age (P > 0.001). In the absence or presence of [N.sup.[omega]]-nitro-L-arginine methyl ester (L-NAME) and indomethacin (Indo), maximum responses in 1 (-54.7 [+ or -] 7.4 and -37.9 [+ or -] 3.9%)- and 4 (-48.8 [+ or -] 2.4 and -35.5 [+ or -] 7.8%)-wk-old rabbits were higher than 8 (-30.0 [+ or -] 2.8 and -26.6 [+ or -] 4.4%)-and 16 (-36.7 [+ or -] 3.5 and -27.3 [+ or -] 10%)-wk-old rabbits. A lipoxygenase inhibitor, BW755C, reduced THETA and HEETA synthesis in mesenteric arteries. In the presence of Indo and [N.sup.[omega]]-nitro-L-arginine, ACh relaxations were reduced by BW755C to a greater extent in the mesenteric arteries from the younger rabbits. In 4-wk-old rabbits treated with L-NAME and Indo, the maximum ACh hypotension was reduced by the potassium channel inhibitors apamin and charybdotoxin to -6.9 [+ or -] 0.9%, by apamin alone to -19.5 [+ or -] 1.4%, and by BW755C to -18.8 [+ or -] 3.5%. The present study indicates that the age-related decrease in ACh-induced hypotension is mediated by the decreased synthesis of the 15-LO-1 metabolites THETAs and HEETAs. endothelium-derived hyperpolarizing factor; arachidonic acid; vasodilation; mean arterial pressure