Potassium adaptation in hypothyroidism: changes in transport adenosinetriphosphatases.

To evaluate whether hypothyroidism alters the adaptive responses of renal transport adenosine-triphosphatases (ATPases) to modifications in dietary K content, we examined the activities of Na-K pump and H-K pump in hypothyroid rats under basal conditions and after dietary K changes. Hypothyroidism led to a decline in Na-K pump activity in all three nephron segments examined [proximal convoluted tubule from 2,333 +/- 103 to 1,099 +/- 32, medullary thick ascending limb from 4,344 +/- 119 to 1,613 +/- 61, and cortical collecting tubule (CCT) from 1,133 +/- 45 to 640 +/- 38 pmol.mm-1 x h-1; all P < 0.01 vs. euthyroid] along with morphological changes manifest in a decrease in tubule diameter. K loading led to an increase in Na-K pump activity in the CCT of both euthyroid (from 1,133 +/- 45 to 2,269 +/- 74, pmol.mm-1 x h-1, P < 0.01) and hypothyroid (from 640 +/- 38 to 1,118 +/- 67 pmol.mm-1 x h-1, P < 0.01) animals. Furthermore, in euthyroid rats, 3 wk of K depletion led to a major increase in H-K pump activity in both the CCT (from 203 +/- 14 to 331 +/- 22 pmol.mm-1 x h-1, P < 0.01) and medullary collecting tubule (MCT, from 137 +/- 9 to 210 +/- 14 pmol.mm-1 x h-1, P < 0.01). Hypothyroidism was associated with a decline in H-K pump activity in the CCT and MCT (to 94 +/- 6 and 55 +/- 5 pmol.mm-1 x h-1, respectively; both P < 0.01 vs. euthyroid).(ABSTRACT TRUNCATED AT 250 WORDS)