Different effects of dopamine and dopexamine on the isolated perfused rat kidney

We have investigated the effect of dopamine and dopexamine on the isolated perfused rat kidney. After an equilibration period of 20 min and two control periods of 10 min, dopexamine 1.0, 2.5 or 4.0 micrograms kg-1 min-1 or dopamine 2.0 micrograms kg-1 min-1 were perfused for a further 40 min in random order. Renal blood flow, urine volume, glomerular filtration rate, absolute sodium excretion and fractional sodium reabsorption of the isolated perfused kidney were measured every 10 min during the experiment. Dopamine increased significantly urine production from mean 61.54 (SEM 4.7) to 117.2 (9.7) microliters min-1 g-1 and absolute sodium excretion from 0.4 (0.1) to 1.2 (0.1) mumol min-1 g-1, and decreased significantly fractional sodium reabsorption from 97.3 (0.5) to 90.7 (0.7)%. Renal blood flow and glomerular filtration rate were not altered. In contrast, dopexamine had no effect on the isolated kidney. These data suggest that the diuretic and natriuretic effects of dopexamine in humans may not result from a direct action on the kidney.