Time-dependent changes in inner medullary plasma flow rate during potassium-depletion.

Renal concentrating ability becomes impaired after approximately 2 weeks of dietary potassium (K) depletion in the rat. Since inner medullary plasma flow (IMPF) has been shown to be reduced after 3 weeks of K-depletion, IMPF was measured after 2 and 3 weeks of dietary K-deprivation to determine if the change in IMPF is present at the time the renal concentrating defect first appears. In the present study, similar reductions in maximal urine concentration were present in rats K-depleted for 2 and 3 weeks. IMPF measured by the 125I albumin accumulation method, however, was normal after 2 weeks of K-depletion (control, 35.1 +/- 1.93 vs. K-depletion 2 weeks, 32.8 +/- 1.52 ml/min/100 g IM), and was reduced after 3 weeks of this dietary regime (K-depletion, 3 weeks: 13.8 +/- 1.84). To determine the mechanism of the decrease in IMPF after 3 weeks of K-depletion, rats were treated acutely with indomethacin. There was no significant change in IMPF in control or 3-week K-depleted rats following treatment with indomethacin. These results suggest that the reduction in medullary solute content after 2 weeks of K-depletion cannot be attributed to a reduction in IMPF. In addition, products of the cyclooxygenase enzyme systems do not appear to contribute in a major way to the reduction in IMPF measured after 3 weeks of dietary K-depletion.