Adaptive myocardial hypertrophy in the renal ablation model

We have previously reported downregulation of the vascular alpha 1-receptor in the 5/6 renal ablation model. In this investigation we have examined the adaptive response of the heart following 5/6 renal ablation. Renal ablated and sham rats were maintained under identical conditions for 6 weeks. Despite the presence of systemic hypertension in renal ablated rats (185 +/- 10 mm Hg, P less than .01), heart weight did not differ from sham. [125I] +/- CYP binding was performed and myocardial norepinephrine (NE) content determined to evaluate myocardial sympathetic neuroeffector mechanisms. Scatchard analysis and 1-isoproterenol competition curves did not reveal a difference in the binding properties of the myocardial beta-receptor. No difference in myocardial NE was found in renal ablated and sham rats. Unexpectedly, 1-isoproterenol stimulation of adenylate cyclase was impaired in renal ablated rats (32.6 +/- 6 v 58.6 +/- 5 pmol/mg/min, P less than .01) and the dose response curve shifted to the right. We conclude that despite systemic hypertension an adaptive hypertrophic response was not present in hearts of renal ablated rats; myocardial sympathetic neuroeffector mechanisms are not altered in this model; and impaired stimulation of adenylate cyclase appears to be the result of a post-receptor defect.