The effect of intravenous contrast medium on glomerular filtration rate

The changes in glomerular filtration rate (GFR) after intravenous contrast medium have been investigated with three contrast media of differing osmolality (monomer, dimer and non-ionic agent) in antidiuretic dogs with three different basal solute excretion rates. A transient increase in GFR after contrast medium was attributed to the wash-out of medullary creatinine at the onset of diuresis. The subsequent fall in GFR was greatest with the contrast media of higher osmolality and in those dogs without an underlying solute diuresis. With the monomer, the decrease in GFR produced a significant decrease in the amount of contrast medium excreted in the first few minutes after contrast injection. It is suggested that an important factor in the decrease in GFR is the rise in pressure in the renal tubules at the start of a diuresis, before they have had time to dilate. An underlying solute diuresis is considered to protect against the fall in GFR because tubular dilatation has already occurred in response to the basal solute load. The decrease in blood pressure during and after contrast medium injection did not correlate with the fall in GFR.