NA-ATPASE AND ACETYLCHOLINESTERASE ACTIVITIES - CHANGES IN POSTNATALLY DEVELOPING RAT-BRAIN INDUCED BY BILIRUBIN(,K+)

Na+,K+-ATPase, Mg++-ATPase, and acetylcholinesterase activities were d etermined in brain homogenates of rats in different ages, which were d ecapitated 30 min after administration of various bilirubin doses. Bil irubin serum and brain tissue levels should be dependent upon the dose administered. At these concentrations, a progressive enzyme inactivat ion was observed, which reached 25-30% for acetylcholinesterase and 70 -80% for Na+,K+-ATPase in neonate rats and 15-20% for acetylcholineste rase and only 30-40% for Na+,K+-ATPase in the brain of aged rats (20 m o). However, Mg++-ATPase activity was not affected by bilirubin deposi tion in the developing brain. Moreover, brain albumin content increase d 53% in suckling, 40% in adult, and 33% in aged rats at high drug adm inistration. These results may indicate an opening of the blood-brain barrier and a bilirubin entry into the rat brain. The bilirubin immedi ate toxic effects on brain acetylcholinesterase and Na+,K+-ATPase, and probably on brain electrical activity, may be modulated by the develo pmental state of membrane-bound enzymes.