642 HEPATIC NA, K-ATPASE DEVELOPMENT IN THE RAT: IMPLICATIONS FOR “PHYSIOLOGIC CHOLESTASIS”

Abstract

Na, K-ATPase (NKA) is an important enzyme for the hepatic uptake of bile acids, a process thought to be immature in neonatal liver i.e. “physiologic cholestasis”. The development of NKA activity was studied in Sprague-Dawley rats: fetal 18-20 d, newborn 1, 3, 5, 7, 10, and 14 d, and adult. NKA activity was measured in both a crude homogenate (CH) and a plasma membrane (PM) fraction, using a system containing phosphoenolpyruvate and pyruvate kinase to prevent product inhibition by ADP (Alcoholism 8:390, Am J Phys 238:E38). NKA activity in the PM fraction per gram liver was comparable to that of the CH. A similar, but less striking pattern was seen when activity was expressed per mg protein. Hepatic NKA activity shows a developmental pattern which has not reached adult levels by 14 d. The “physiologic cholestasis” of the human neonate may be due in part to insufficient Na, K-ATPase activity.