Role of dietary potassium in the hyperaldosteronism and hypertension of the remnant kidney model.

Abstract

The remnant kidney model of progressive renal disease is marked by arterial hypertension, especially when produced by nephrectomy and partial infarction. Hyperaldosteronism sustains much of the hypertension, but the stimuli to the increased aldosterone levels are uncertain. It is hypothesized that the hyperaldosteronism attending this model stems from the combination of fixed dietary potassium load in the face of reduced filtration on the one hand, and persistent renin secretion from the scarred remnant kidney on the other. This hypothesis predicted that dietary potassium restriction would lower aldosterone and BP in this model. To test this prediction, two groups of rats with a remnant kidney were studied. Group 1 consumed 0.4 +/- 0.06 mEq (mean +/- SD) of potassium chloride daily, and group 2 ate 4.8 +/- 1.0 mEq daily. Two sham-operated groups with intact kidneys also were studied. Group 3 consumed 1.7 +/- 0.2 mEq daily and group 4 ate 15.2 +/- 1.4 mEq daily. These levels of intake were designed to provide at least as much potassium per liter of GFR in the sham groups as in the remnant kidney rats. Systolic BP (SBP), 24-h protein excretion, plasma aldosterone levels, 24-h urinary aldosterone excretion, and plasma renin activity (PRA) were determined in all groups at 2 wk. At 4 wk, after SBP and protein excretion measurements, remnant kidneys were perfusion-fixed for morphometric analysis. SBP was normal in both sham-operated groups and was not different between the groups (113 +/- 13 versus 117 +/- 2 mmHg, group 3 versus group 4). In the remnant animals, SBP at 2 wk followed potassium intake: Group 1 had a lower SBP than group 2 (140 +/- 26 versus 170 +/- 34 mmHg, P = 0.005). The same SBP pattern persisted at 4 wk (153 +/- 25 versus 197 +/- 27 mmHg, group 1 versus group 2, P = 0.0006). However, 24-h urinary protein excretion was not different between the two groups with remnant kidneys at either 2 or 4 wk. Both plasma and 24-h urinary aldosterone excretion at 2 wk followed potassium intake (120 +/- 124 versus 580 +/- 442 pg/ml for plasma aldosterone, group 1 versus group 2, P = 0.03, and 2.6 +/- 1.8 versus 23.2 +/-9.8 ng/d for urinary aldosterone, group 1 versus group 2, P = 0.0001). PRA, however, followed a reverse pattern in which dietary potassium restriction resulted in higher levels (16 +/- 6 versus 6 +/- 3 ng angiotensin I/ml per h, group 1 versus group 2, P = 0.01). A similar pattern for PRA and aldosterone excretion was also observed in the sham groups, in which lower potassium intake also resulted in a significantly higher PRA and lower aldosterone excretion. The constancy of BP in the sham groups likely reflects their lack of nephron reduction and greater sodium excretory capacity. Morphometric analysis in remnant animals revealed no significant difference between the two dietary groups in the prevalence of glomerular sclerosis, glomerular volume, or interstitial volume. It is concluded that dietary potassium is a potent determinant of hypertension in the remnant kidney model probably through the actions of aldosterone and that the high aldosterone secretion in this model is a function of the dietary potassium load. In this model, reduction in nephron number is also critical in promoting hypertension in conjunction with hyperaldosteronism.