Stress susceptibility as a determinant of endothelium-dependent vascular reactivity in rat mesenteric arteries

In order to investigate the consequences of stress susceptibility on vascular function, the authors assessed the respective contributions of nitric oxide (NO), prostanoids, and endothelium-derived hyperpolarizing factor to the vascular tone in rats with a constitutionally determined high and low susceptibility to behavioral stressors. In mesenteric resistance arteries mounted in a small vessel myograph and precontracted with I-phenylephrine hydrochloride (phenylephrine), the NO-synthase inhibitor N-w-nitro-L-arginine (L-NOARG, 100 muM) elicited a smaller increase of vascular tone in apomorphine-susceptible (APO-SUS) rats (P < 0.01). Addition of indomethacin (10 muM), in the presence of L-NOARG, resulted in a smaller decrease of vascular tone in APO-SUS rats (P < 0.01). Although acetylcholine-induced relaxation in phenylephrine-precontracted arteries was not different (P > 0.1), the individual components contributing to this relaxation were. In arteries precontracted with 125 mMK(+), and incubated with indomethacin, acetylcholine-induced relaxation was not significantly different (pEC(50) and E-max: P > 0.1). Sensitivity (pEC(50): P < 0.05) and maximum relaxation (E-max: P < 0.001) to sodium nitroprusside, in the presence of 125 mMK(+), was more pronounced in APO-SUS rats. In phenylephrine-precontracted arteries, in the presence of L-NOARG and indomethacin, maximum relaxation to ACh was reduced in APO-SUS rats (E-max: P < 0.05). This study showed that in rats with a high susceptibility to stressors, the contribution of NO to vascular tone was decreased as was the ratio of vasoconstrictor and vasodilator cyclooxygenase products in alpha-adrenergic precontracted arteries. End-organ sensitivity to NO was greater in APO-SUS rats, possibly due to up-regulation. Moreover, the contribution of endothelium-derived hyperpolarizing factor to acetylcholine-induced vasodilation was reduced in APO-SUS rat arteries.