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ABESTRACT: Introduction & Objective: 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. Materials and methods: 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 22nd 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. Results: 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. Conclusion: 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. Keywords: Preeclampsia, L-NAME, Diazoxide, Thoracic aorta, Rat.

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Introduction & Objectives: Recently, the findings of some studies have shown that, nitric oxide (NO) probably has an important role in differentiation of mesenchymal stem cells to osteoblasts. The aim of the present investigation was to study the effects of nitric oxide production inhibitor named, NG-nitro-L-arginine methyl ester (L-NAME), on rat mesenchymal stem cells differentiation to osteoblasts in vitro. Materials & Methods: This was an experimental study conducted at Hamedan University of Medical Sciences in 2009, in which rat bone marrow stem cells were isolated in an aseptic condition and cultured in vitro. After third passage, the cells were cultured in osteogenic differentiation medium. To study the effects of L-NAME on osteogenic differentiation, the L-NAME was added to the culture medium at a concentration of 125, 250, and 500 μM in some culture plates. During the culture procedure, the media were replaced with fresh ones, with a three days interval. After 28 days of culturing the mineralized matrix was stained using Alizarian red staining method. The gathered data were analyzed by SPSS software version 12 using one way ANOVA. Results: The findings of this study showed that in the presence of L-NAME, differentiation of bone marrow mesenchymal stem cells to osteoblasts was disordered and matrix mineralization significantly decreased in a dose dependent manner. Conclusion: This study revealed that, inhibition of nitric oxide production using L-NAME can prevent the differentiation of rat bone marrow mesenchymal stem cells to osteoblast. The results imply that NO is an important constituent in differentiation of mesenchymal stem cell to osteoblasts.