Acetylcholine-induced relaxation of rat aorta is greatest during estrus in the sexual cycle

Increase in insulin-induced relaxation of consecutive arterial segments toward the periphery: Role of vascular oxidative state

RATIONALE

The oxidative state has been implicated in the signaling of various vasomotor functions, yet its role regarding the vasomotor action of insulin is less known.

OBJECTIVE

To investigate the insulin-evoked relaxations of consecutive arterial segments of different oxidative state and the role of extracellular signal-regulated kinase (ERK) pathway.

METHODS AND RESULTS

The oxidative state, as assessed by the level of ortho-tyrosine, was higher in the thoracic aorta of rats than in the abdominal aorta, and was the lowest in the femoral artery. The vasomotor function of vessels of same origin was studied using a small-vessel myograph. Insulin-induced relaxations increased toward the periphery (i.e., thoracic < abdominal < femoral). Aortic banding and hydrogen peroxide/aminotriazole increased the oxidative state of the thoracic aorta that was accompanied by ERK activation and decreased relaxation to insulin, and vice versa, acutely lowered oxidative state by superoxide dismutase/catalase improved relaxation. In contrast, insulin-induced relaxation of the femoral artery could be enhanced with a higher oxidative state, and reduced with a lower state.

CONCLUSIONS

Oxidative state of vessels modulates the magnitude of vasomotor responses to insulin, which appears to be mediated via the ERK signaling pathway.

A variation in acetylcholine-induced relaxation of rat aorta in pregnancy

The tension of isolated ring preparations of the thoracic aortae from pregnant rats on Days 7, 14, and 21 was measured isometrically to study the effect of advancing pregnant stage on endothelium-dependent relaxing factor activity. The endothelium-dependent relaxation caused by acetylcholine (ACh) (10(-8) - 3x10(-5) M) in the aortae of pregnant rats on Days 7, 14, and 21 were greater than that in those of diestrus (D-2) rats. In pregnant rats, the endothelium-dependent relaxation caused by acetylcholine was greatest in the aortae from pregnant rats on Day 21. In contrast with ACh, the relaxation caused by sodium nitroprusside was decreased in the aortae from pregnant rats on Day 21, compared with metestrus (D-1) and estrus (E) rats. The peaks of serum estradiol and progesterone levels in pregnant rats were observed on Days 21 and 14, respectively. These results suggest that there is a fluctuation of endothelium-dependent relaxing factor activity in the aortae during pregnancy of rats and ACh-induced relaxation is greatest on Day 21 in pregnancy, and that it may be due to the enhancement of NO synthesis in endothelium mainly by estradiol and partly by progesterone.

17Beta-estradiol alters isoproterenol-induced relaxation in rat aortic rings

Female Wistar rats were treated with 17beta-estradiol (E2) (10 microg, s.c.) or with sesame oil for 3 days. The relaxation induced by isoproterenol (10(-9)-3 x 10(-6) M) in aortae precontracted with norepinephrine was significantly suppressed in aortae from E2-treated rats compared with the relaxation in those from control rats. N(G)-Nitro-L-arginine, a nitric oxide synthase inhibitor, inhibited isoproterenol-induced relaxation in aortae from both E2-treated and control rats. Metyrapone, a cytochrome P-450 monooxygenase inhibitor, inhibited it in aortae from control rats, but metyrapone enhanced the maximum relaxation in aortae from E2-treated rats. These results suggest that E2 modulates isoproterenol-induced vasodilation through nitric oxide and cytochrome P-450-dependent metabolites.