The presence of LOCM such as Uttravist in the blood stream encourages lowering of blood\viscosity v ia osmodilution. LOCM passes in to glomerular filtrate. Residual hyperosmolality of filtrate increases osmotic pressure of tubular fluid and reduces water reabsorption. More water is retained in tubules, d iluting and further lowering viscosity of tubular fluid (osmodiuresis-). Preserved GFR and fluid flow through tubules and renal blood vessels.