Na+,K(+)-ATPase and acetylcholinesterase activities: changes in postnatally developing rat brain induced by bilirubin.

Na+,K(+)-ATPase, Mg(++)-ATPase, and acetylcholinesterase activities were determined in brain homogenates of rats in different ages, which were decapitated 30 min after administration of various bilirubin doses. Bilirubin serum and brain tissue levels should be dependent upon the dose administered. At these concentrations, a progressive enzyme inactivation was observed, which reached 25-30% for acetylcholinesterase and 70-80% for Na+,K(+)-ATPase in neonate rats and 15-20% for acetylcholinesterase and only 30-40% for Na+,K(+)-ATPase in the brain of aged rats (20 mo). However, Mg(++)-ATPase activity was not affected by bilirubin deposition in the developing brain. Moreover, brain albumin content increased 53% in suckling, 40% in adult, and 33% in aged rats at high drug administration. These results may indicate an opening of the blood-brain barrier and a bilirubin entry into the rat brain. The bilirubin immediate toxic effects on brain acetylcholinesterase and Na+,K(+)-ATPase, and probably on brain electrical activity, may be modulated by the developmental state of membrane-bound enzymes.