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

Abstract

Arachidonic acid (AA) metabolites from the 15-lipoxygenase-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^ω-nitro-l-arginine methyl ester (l-NAME) and indomethacin (Indo), maximum responses in 1 (−54.7 ± 7.4 and −37.9 ± 3.9%)- and 4 (−48.8 ± 2.4 and −35.5 ± 7.8%)-wk-old rabbits were higher than 8 (−30.0 ± 2.8 and −26.6 ± 4.4%)- and 16 (−36.7 ± 3.5 and −27.3 ± 10%)-wk-old rabbits. A lipoxygenase inhibitor, BW755C, reduced THETA and HEETA synthesis in mesenteric arteries. In the presence of Indo and N^ω-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 ± 0.9%, by apamin alone to −19.5 ± 1.4%, and by BW755C to −18.8 ± 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.