Our previous experiments demonstrated that selective endothelin A (ETA) receptor blockade had antihypertensive effects in Ren-2 transgenic rats (TGRs), but the mechanisms responsible for this change of blood pressure (BP) have not been explored yet.Method:
Four-week-old male heterozygous TGRs and their normotensive controls – Hannover Sprague–Dawley (HanSD) rats – were fed high-salt diet (2% NaCl) and were treated with selective ETA receptor blocker atrasentan (5 mg/kg per day) for 8 weeks. At the end of the study, the contribution of principle vasoactive systems was evaluated by the sequential blockade of the renin–angiotensin system (captopril), sympathetic nervous system (pentolinium) and nitric oxide synthase [Nω-nitro-L-arginine methyl ester (L-NAME)]. The role of calcium influx through L-type voltage-dependent calcium channels in BP maintenance was evaluated using nifedipine. In a separate group of animals, the efficiency of distinct vasodilator systems – prostanoids (blocked by nonselective cyclooxygenase inhibitor indomethacin) and Ca2+-activated K+ channels (inhibited by tetraethylammonium) – was also analyzed.Results:
Atrasentan attenuated the development of hypertension in heterozygous TGRs, but had no effects in Hannover Sprague–Dawley rats. Moreover, atrasentan moderately attenuated renin–angiotensin system-dependent vasoconstriction, whereas it had no effect on sympathetic vasoconstriction. The nifedipine-sensitive BP component was markedly decreased by atrasentan treatment. In contrast, vasodilatation mediated by nitric oxide, endogenous prostanoids or Ca2+-activated K+ channels was reduced in atrasentan-treated TGRs, indicating the absence of compensatory augmentation of endothelin B receptor-mediated vasodilation in these animals.Conclusion:
BP-lowering effect of chronic atrasentan treatment in TGRs was mainly caused by reduced Ca2+ influx through L-type voltage-dependent calcium channels due to missing ETA receptor-dependent vasoconstriction and attenuated angiotensin II-dependent vasoconstriction.