Jejunal dopamine and Na+,K+-ATPase activity in early chronic renal insufficiency

Abstract

Aim: The uninephrectomised and three-quarter nephrectomised (3/4nx) rats present dopamine-sensitive enhanced natriuresis. This is accompanied in uninephrectomised rats by a reduced jejunal Na+,K+-ATPase activity with recovered sensitivity to inhibition by dopamine. The present study examined the jejunal Na+,K+-ATPase activity and the role of dopamine in 3/4nx animals. Methods: Fourteen days after surgery, the L-amino acid decarboxylase activity (AADC) activity, the enzyme responsible for the synthesis of dopamine, and the Na+,K+-ATPase activity, were determined in jejunal epithelial cells from 3/4nx and Sham rats. In addition, the effect of dopamine (1 mu mol/L) on jejunal Na+,K+-ATPase activity was evaluated in both groups. Results: The 3/4nx rats presented a reduced AADC activity in jejunal epithelial cells (V-max in nmol/mg prot/15 min, 142 +/- 6 vs 190 +/- 10, P < 0.05). In addition, the jejunal Na+,K+-ATPase activity was increased in 3/4nx rats (Pi release in nmol/mg prot/min, 137 +/- 1 vs 122 +/- 2, P < 0.05). However, dopamine was unable to inhibit the Na+,K+-ATPase activity in jejunal epithelial cells from both 3/4nx and Sham animals. Conclusions: In contrast to uninephrectomy, the jejunal Na+,K+-ATPase activity is increased in 3/4nx rats and is not sensitive to inhibition by dopamine.