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

The tension of isolated ring preparations of the thoracic aortae from pregn ant rats on Days 7, 14, and 21 was measured isometrically to study the effe ct of advancing pregnant stage on endothelium-dependent relaxing factor act ivity. The endothelium-dependent relaxation caused by acetylcholine (ACh) ( 10(-8)-3 x 10(-5) M) in the aortae of pregnant rats on Days 7, 14, and 21 w ere greater than that in those of diestrus (D-2) rats. In pregnant rats, th e endothelium-dependent relaxation caused by acetylcholine was greatest in the aortae from pregnant rats on Day 21. In contrast with ACh, the relaxati on caused by sodium nitroprusside was decreased in the aortae from pregnant rats on Day 21, compared with metestrus (D-l) and estrus (E) rats. The pea ks of serum estradiol and progesterone levels in pregnant rats were observe d on Days 21 and 14, respectively. These results suggest that there is a fl uctuation of endothelium-dependent relaxing factor activity in the aortae d uring 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 en dothelium mainly by estradiol and partly by progesterone. (C) 1998 Elsevier Science Inc.