[Effects of phenylephrine, calcium, Acetylcholine and Diazoxide on isolated Aorta of preeclamptic rats]

Preeclampsia, one of the most significant health problems in human pregnancy, is a leading cause of fetal mortality and maternal death. Alteration in vascular response to vasopressors and vasodilators is proposed as a major change in the context of preeclampsia. The aim of the present study was to investigate the responsiveness of preeclamptic rat aorta to some vasopressors and vasodilators. This experimental study was carried out in the pharmacology department of Shiraz University of Medical Sciences in 2008. Thirty pregnant rats were randomly divided into two groups [15 rats in each group]: case group received L-NAME at a dose of 50 mg/kg through drinking water from day 11 of pregnancy. Control group received only tap water. On the 22[nd] gestational day, all rats were anesthetized and killed; thoracic aorta was isolated, cut into 2-3 mm rings and mounted in organ bath. The isolated aortic rings were then exposed to cumulative concentrations of phenylepherine [Ph] and calcium, separately and contractions were measured by isometric transducers. To study the relaxing responses of aortic segments to vasodilators, the effects of cumulative concentrations of acetylcholine [Ach] and diazoxide on aortic rings precontracted with Ph and potassium were recorded, respectively. SPSS software and unpaired T-Test were used for data analysis. Potency of phenyepherine to contract rat aorta was significantly higher in preeclamptic rats compared to normal pregnant group [P= 0.014] but there was no significant difference in Ph-induced maximum contraction between two groups. Potency of Ach and its maximum relaxation effect was significantly lower in preeclamptic rats compared to controls, [p values were 0.026 and 0.004, respectively]. There were no statistically significant differences in the contractile responses of calcium and relaxing effects of diazoxide between two groups. Experimental preeclampsia increases the sensitivity of rat aorta to alpha- adrenergic receptor agonists and decreases the endothelium-dependent relaxation of it. It seems that the functions of voltage-operated calcium channels and ATP-dependent potassium channels do not change in experimental preeclampsia