Pressor and renal haemodynamic responses to angiotensin II (ANG II) in conscious lambs: Role of nitric oxide (NO) and prostaglandins (PGs)

Abstract

Previously, we showed in conscious lambs that pressor and renal haemodynamic responses to ANG II were greater at ∼six weeks as compared to newborns aged ∼one week. The present study investigated the roles of NO and PGs in modulating these responses to ANG II during post natal maturation. Two experiments were carried out at an interval of 24 h in two age groups of conscious, chronically instrumented lambs: ∼one week (N=8) and ∼six weeks (N=10). Acute arterial pressure (AP) and renal blood flow (RBF) responses to intra‐venous (I.V.) injection of EC50 ANG II were tested before and after administration of the L‐arginine analogue, NG‐nitro‐L‐arginine methyl ester (L‐NAME), in the presence of either vehicle (veh, experiment one) or indomethacin (indo, experiment two). In both age groups, L‐NAME had no effects on the AP and RBF responses to ANG II after veh. In contrast, after indo, AP and RBF responses to L‐NAME were increased at one week but not at six weeks. Therefore, there is an age‐dependent interaction between NO and PGs in buffering the pressor and renal haemodynamic effects of ANG II soon after birth.