THE EFFECT OF SODIUM IOTHALAMATE ON THE VASCULAR-RESISTANCE OF THE ISOLATED PERFUSED RAT-KIDNEY

The direct effects of sodium iothalamate on renal vascular resistance (RVR) were examined using the isolated perfused rat kidney experimental model. A concentration-dependent biphasic change in RVR was produced with the hyperosmolar solution of sodium iothalamate [(Conray 420), 420 mgI/ml, 2500 mOsmol/kg/H2O]. The response characterized by an initial fall followed by a prolonged increase in RVR on discontinuation of the iothalamate infusion. No significant change in RVR was observed when iothalamate was infused as an iso-osmotic solution (60 mgI/ml, 280 mOsmol/kg/H2O) at a rate of 0.525 ml/min. to produce a concentration of 4.2 mgI/ml in the renal perfusate. We conclude that sodium iothalamate can exert direct biphasic effects on RVR which are mediated by its hyperosmolality rather than its chemical content.