Effect of L-dopa treatment on cerebral amino acid levels in rats after portocaval anastomosis.

Abstract

L-Dopa therapy has been suggested as effective in the reversal of hepatic coma both in humans and in animals. Beneficial effects have been reported also in chronic hepatic encephalopathy. There are many possible mechanisms through which L-dopa could ameliorate this pathological state. The present study was carried out to clarify whether the L-dopa effect could be mediated through an improvement of the brain neutral amino acid patterns, since it competes for the same transport carrier at the blood-brain barrier. A first group of rats was orally administered L-dopa (10 mg/100 g body weight daily) for 1 month following portocaval anastomosis. A second group was intraperitoneally injected (1.5 mg/100 g body weight daily) for 1 week, a month after portocaval shunt. Amino acid levels were determined in plasma and in four cerebral regions. No beneficial effects were observed clinically (in general condition, body weight, or hypertonic posture) in rats receiving L-dopa compared to controls. The large increase of tyrosine, phenylalanine, tryptophan, histidine, and glutamine that occurs in the cerebral tissue after portocaval shunt was also not affected by L-dopa administration. In conclusion, in this experimental condition we had no clinical improvement in shunted animals receiving L-dopa. Moreover, this compound did not seem to influence the pathological increase of aromatic amino acids in the brain, which is considered to play an important role in hepatic encephalopathy.