Effect of indomethacin on intrarenal circulation and sodium and water excretion in anaesthetised rats with or without acute volume expansion.

Effects of the prostaglandin synthesis inhibitor indomethacin (4 mg/kg) were studied on the intrarenal circulation of anaesthetised (pentothal 50 mg/kg i.p.) rats in normovolemia or subjected to acute extracellular volume expansion (intravenous infusion of 0.9% NaCl at a dose of 50 ml/kg) using Sapirstein's 86Rb indicator dilution technique. Circulatory parameters were determined one hour after indomethacin treatment. The following conclusions were drawn: 1. In normovolemic rats the renal, cortical and medullary blood flow remained unaltered. No changes occurred in regional vascular resistances of the kidney or in the distribution pattern of intrarenal blood flow. Water output was moderately reduced while sodium excretion remained unaffected. 2. In rats subjected to acute extracellular volume expansion renal cortical blood flow was slightly augmented, medullary perfusion rate declined; the intrarenal blood flow distribution was shifted towards the cortex. The vascular resistance in the cortex did not change whereas that in the medulla was slightly augmented. Under these conditions indomethacin did not influence salt and water excretion. Our results provide further evidence that unlike in anaesthetised dog, in the anaesthetised rat endogenous prostaglandins probably do not play a decisive role in the control of renal blood flow, intrarenal circulation and salt and water excretion.