EFFECT OF ORTHOTOPIC LIVER-TRANSPLANTATION AND CHEMICAL DENERVATION OF THE LIVER ON THE ACTIVITIES OF HEPATIC MONOAMINE-OXIDASE AND CATECHOL-O-METHYLTRANSFERASE

The denervation of some tissues is associated with a fall in the activ ities of monoamine oxidase (MAO) and catechol-O-methyltransferase (COM T). Here we report on the effect of orthotopic liver transplantation a nd chemical denervation of the liver on the enzymes. Liver transplanta tion was performed on Lewis rats (n=7). Denervation (n=8) was by intra portal injection of 6-hydroxydopamine (75 mg/kg). A control group (n=8 ) was also included. The norepinephrine content of the transplanted an d denervated livers was reduced by greater than 99% (P<0.001) and 95% (P<0.001), respectively. The activity of hepatic COMT (substrate: cate chol 5 mM!) was not affected by transplantation or denervation. The a ctivity of MAO with 0.1 mM 5-hydroxytryptamine (5-HT) (substrate for M AO-A) and with 0.01 mM 2-phenylethylamine (substrate for MAO-B) were n ot affected by denervation. In the transplanted liver, the activity of MAO with 5-HT and 2-phenylethylamine was increased by 26% (P<0.05) an d by 53% (P<0.001), respectively. The ratios of the activities of the A to B forms of MAO (approximately 70% A to 30% B) was not affected by either procedure. Enzyme sensitivity for MAO inhibitors clorgyline an d deprenyl were not significantly altered by transplantation. The conc entration of plasma norepinephrine in the transplantation group was si gnificantly lower than either the control (P<0.001) or denervation gro ups (P<0.05). We conclude from our results that the metabolism of circ ulating catecholamines by the liver is unlikely to be impaired after l iver transplantation.