Direct effects of lead (Pb2+) on the relaxation of in vitro cultured rat aorta to acetylcholine

Lead (Pb2+) exposure is related to increased blood pressure or hypertension of human or animals. Abnormal vascular relaxant responses of low level Pb2+ exposed animals were reported by several studies. However, it is difficult to tell whether these effects were induced directly by Pb2+ or not. In this study we hypothesized that Pb2+ can directly affect the relaxation of vessels. Male Wistar rat aortae were removed and cultured in PMRI 1640 with 1 ppm Pb2+ (4.8 μM lead acetate) for 0.5, 6, 12 and 24 h, and then their responses to acetylcholine (ACh) and sodium nitroprusside (SNP) were examined. After incubated for 24 h, the relaxation induced by ACh was significantly decreased in Pb2+ exposed aortic rings. However, there was not significant difference in relaxation induced by SNP between Pb2+ exposed and control group. The nitrite in the culture media of aortic rings cultured for 24 h, measured with Griess method, was significantly decreased in the Pb2+ exposed group. The expression of endothelial NOS (eNOS) and isoform NOS (iNOS) in the homogenate of aortic rings cultured for 24 h was measured by Western blot. The expression of eNOS of the Pb2+ exposed group was significantly upregulated compared with that of the control group. However, there was no significant difference in the expression of iNOS in control and Pb2+ exposed group. In conclusion, Pb2+ was able to directly affect the relaxation of rat aorta. This effect may have some relation with the lower level of NO in the media, though the expression of eNOS was upregulated.