RENAL ACTIONS OF THE ANGIOTENSIN AT(2) RECEPTOR LIGANDS CGP-42112 AND PD-123319 AFTER BLOCKADE OF THE RENIN-ANGIOTENSIN SYSTEM

The purpose of this study was to investigate whether the selective angiotensin AT(2) receptor ligands, CGP 42112B (Nic-Tyr-(N-a-benzoyloxycarbonyl-Arg)Lys-His-Pro-Ile-OH) and PD 123319 ((s)-1-[[4-(dimethylamino)-3-methyl-phenyl]methyl]- 5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo[4,5-c]-pyridine-6-carboxylic acid) are agonists at angiotensin receptors influencing blood pressure and renal function in the enalaprilat-treated anesthetized rat. The agonist angiotensin II significantly increased blood pressure and renal vascular resistance. Glomerular filtration rate was unchanged by angiotensin II. Effective renal blood flow decreased significantly in response to angiotensin II leading to a significant increase in filtration fraction. Angiotensin II did not induce significant change in urinary potassium excretion or free water formation but significantly increased both urine volume and urinary sodium excretion. At doses up to 3 orders of magnitude greater than angiotensin II, CGP 42112B also significantly increased blood pressure, filtration fraction, glomerular filtration rate, urine volume and urinary sodium excretion, but did not significantly affect effective renal blood flow or renal vascular resistance. The selective angiotensin AT(2) receptor ligand PD 123319 had no significant effects on blood pressure nor any measured parameter of renal function. The changes in blood pressure and renal function produced by angiotensin II and CGP 42112B could be completely blocked by the angiotensin AT(1) receptor antagonist losartan. The results therefore only support a role for angiotensin AT(1) receptors and not angiotensin AT(2) receptors in the control of renal function in the rat and demonstrate that at high doses the angiotensin AT(2) selective ligand CGP 42112B behaves as an agonist at angiotensin AT(2) receptors.