Na,K-ATPase in isolated nephron segments in rats with experimental heart failure.

To characterize renal transport of Na+ in heart failure, urinary Na+ excretion (UNaV), aldosterone levels, and Na,K-ATPase activity in isolated nephron segments were determined in three groups: control rats, rats with heart failure and moderate sodium retention, and rats with heart failure and severe sodium retention. Heart failure was induced by a fistula between the aorta and vena cava. For the control group, UNaV was 0.66 +/- 0.04 (mean +/- SEM) mueq/min, and aldosterone was 18.4 +/- 3.5 ng%. Na,K-ATPase activity (in 10(-11) mol/mm/min) was 28.4 +/- 1.1 in the proximal convoluted tubule, 23.3 +/- 1.0 in the proximal straight tubule, 37.4 +/- 1.9 in the medullary thick ascending limb, 40.2 +/- 1.9 in the cortical thick ascending limb, 43.2 +/- 2.2 in the distal convoluted tubule, and 20.5 +/- 0.9 in the cortical collecting duct. For the group with moderate heart failure, UNaV was 0.35 +/- 0.02 (p less than 0.001 versus control), and aldosterone was 15.9 +/- 4.4 (p = NS versus control). Na,K-ATPase activity was unchanged in the proximal convoluted tubule, proximal straight tubule, medullary thick ascending limb, and cortical collecting duct, but it increased in the cortical thick ascending limb to 57.7 +/- 3.1 (p less than 0.001 versus control) and decreased in the distal convoluted tubule to 35.3 +/- 1.2 (p less than 0.005 versus control). For the group with severe heart failure, UNaV was 0.029 +/- 0.016 (p less than 0.001 versus control), and aldosterone was 186.0 +/- 14.8 (p less than 0.001 versus control).(ABSTRACT TRUNCATED AT 250 WORDS)