Hepatic Na, K-ATPase development in the rat

The development of the enzyme Na.K-ATPase was studied in hepatic tissue from Sprague-Dawley rats at 18-20 days of gestation. 1. 3, 5. 7, 14, 21, and 30 days, and young adulthood (45 days). A developmental pattern was demonstrated for total and membrane-associated Na,K-ATPase activity. The activity in tissue homogenate, expressed per gram tissue, increased from late fetal life, 43.4 ± 1.3 μmol P₁g liver¹h¹'.until 21 days of age, when an adult level of 187.3 ± 19.6 μmol P₁g liver¹h¹was attained. A less pronounced ontogenic pattern was observed when enzyme levels were expressed as specific activity per milligram protein, the activity profile in a crude membrane preparation was similar. The potential for stimulation of enzyme activity by glucocorticoids was studied in ll-day-old animals injected with cortisone acetate (10 mg 100 g body weight^-1) for 3 days. Enzyme specific activity was inducible: Specific activity was greater in cortisone-treated animals, 1.794 ±.043 μmol P₁mg protein^-1h^-1, versus controls, 1.258 ± 0.043 μmol P₁mg protein^-1h^-1(p < 0.01). We postulate that this developmental pattern for hepatic Na,K-ATPase activity may be a reflection of, or a contributing factor in, the ontogeny of sodium-dependent hepatic transport, such as that for bile salts.