Hepatic Na, K‐ATPase Development in the Rat

Abstract

SummaryThe 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 Pig liver−1 h−1.until 21 days of age, when an adult level of 187.3 ± 19.6 μmol Pi g liver −1 h−1 was 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 11‐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 Pi mg protein −1 h −1, versus controls, 1.258 ± 0.043 μmol Pi mg protein−1 h−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.