Reversal of ammonia coma in rats by L-dopa: a peripheral effect

Ammonia coma was produced in rats within 10 to 15 minutes of an intraperitonealinjection of 1.7 mmol NH4CL. This coma was prevented with 1.68 mmol L-dopa given by gastric intubation 15 minutes before the ammonium salt injection. The effect of L-dopa was correlated with a decrease in blood and brain ammonia, an increase in brain dopamine, and an increase in renal excretion of ammonia and urea. Intraventricular infusion of dopamine sufficient to raise the brain dopamine to the same extent did not prevent the ammonia coma nor affect the blood and brain ammonia concentrations. Bilateral nephrectomy eliminated the beneficial effect of L-dopa on blood and brain ammonia and the ammonia coma was not prevented. Thus, the reduction in blood and brain ammonia and the prevention of ammonia coma after L-dopa, can be accounted for by the peripheral effect of dopamine on renal function rather than its central action. These results provide a reasonable explanation for the beneficial effects observed in some encephalopathic patients receiving L-dopa.