Effects of prolactin on Na+K(+)-ATPase activity in the nephron during maturation in the rat

The effect of prolactin (PRL) on renal Na+K(+)-ATPase was investigated in 7-d-old neonatal rats. Animals were treated by bromocriptine (Br; a blocker of endogenous PRL secretion), and the enzyme activity was compared with that of untreated controls. Na+K(+)-ATPase was determined in renal sections in the medullary thick ascending limb of Henle's loop and in the distal tubule by cytochemistry. In the distal tubule, Na+K(+)-ATPase activity was significantly lower in Br-treated animals than in controls (330 +/- 169 versus 558 +/- 146 pmol inorganic phosphate/mm/h, respectively); values did not differ in the medullary thick ascending limb of Henle's loop between Br-treated and control animals (132 +/- 74 versus 165 +/- 113 pmol inorganic phosphate/mm/h, respectively). In vitro effects of PRL were investigated by determining the enzyme activity after incubation of renal sections from Br-treated and untreated animals with different concentrations of PRL. Results suggest that PRL may affect renal Na+K(+)-ATPase activity in the distal tubule in the neonatal period but do not support a major role of PRL in the enzyme maturation.