Endothelial Dysfunction in the Aorta of Transgenic Rats Harboring the Mouse Ren-2 Gene

The renin-angiotensin system plays an important role in the pathophysiology of hypertension. We studied vascular function in the aorta of mouse Ren-2 transgenic rats (TGR(mRen2)27). Changes in isometric tension of isolated aorta of TGR(mRen2)27 and Sprague-Dawley rats (SD) were recorded in organ chambers. Contractions to angiotensin II (AII), big-endothelin and endothelin-1 (ET-1), but not KCl were decreased in TGR. Blockade of nitric oxide (NO)-synthase by L-NAME or removal of the endothelium did not alter these decreased contractions to ET-1 and AII in TGR, suggesting that receptors or signaling pathways of these two agonists are downregulated during hypertension. Contractions to norepinephrine (NE) were also lower in TGR, however blockade of NO-synthase by L-NAME or removal of the endothelium evoked similar contractions to NE in both strains, suggesting that basal release of NO reduces contractions to NE to a greater extent in transgenic than control rats. In the presence of L-NAME, acetylcholine evoked endothelium-dependent contractions (EDCF) in TGR, which were blocked by the thromboxane/prostaglandin H2 receptor antagonists SQ 30741, and partially by the thromboxane synthase inhibitor CGS 13080, suggesting that prostaglandin H2 is the mediator. Endothelium-dependent relaxation to acetylcholine was decreased in TGR, while endothelium-independent relaxations to sodium nitroprusside were similar in both strains. SQ 30741 did not improve relaxations to acetylcholine in TGR indicating that impaired relaxations to acetylcholine are due to a decreased acetylcholine-receptor mediated release of NO rather than increased release of EDCF. Thus, Ren-2 hypertension leads to marked alterations of vascular functions in the aorta. These changes could contribute to hypertension and its vascular complications in TGR(mRen2)27 rats.