Endothelium-dependent relaxation in estrogen-treated spontaneously hypertensive rats.

Female spontaneously hypertensive rats (SHR) were injected subcutaneously with mestranol twice a week for 12 weeks. Isolated segments of thoracic aorta were then used to generate relaxation response curves to acetylcholine or ATP after precontraction with phenylephrine. Estrogen treatment attenuated the development of hypertension. Further, augmented endothelium-dependent relaxation to acetylcholine was seen in the estrogen-treated SHR. There was no difference, however, in the relaxation produced by ATP. Since the relaxation of both acetylcholine and ATP is endothelium-dependent, these findings suggest that different mechanisms may be involved in the relaxation produced by acetylcholine and ATP.