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 activities of monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT). Here we report on the effect of orthotopic liver transplantation and chemical denervation of the liver on the enzymes. Liver transplantation was performed on Lewis rats (n=7). Denervation (n=8) was by intraportal injection of 6-hydroxydopamine (75 mg/kg). A control group (n=8) was also included. The norepinephrine content of the transplanted and denervated livers was reduced by greater than 99% (P<0.001) and 95% (P<0.001), respectively. The activity of hepatic COMT (substrate: catechol [5 mM]) was not affected by transplantation or denervation. The activity of MAO with 0.1 mM 5-hydroxytryptamine (5-HT) (substrate for MAO-A) and with 0.01 mM 2-phenylethylamine (substrate for MAO-B) were not affected by denervation. In the transplanted liver, the activity of MAO with 5-HT and 2-phenylethylamine was increased by 26% (P<0.05) and by 53% (P<0.001), respectively. The ratios of the activities of the A to B forms of MAO (∼70% A to 30% B) was not affected by either procedure. Enzyme sensitivity for MAO inhibitors clorgyline and deprenyl were not significantly altered by transplantation. The concentration of plasma norepinephrine in the transplantation group was significantly lower than either the control (P<0.001) or denervation groups (P<0.05). We conclude from our results that the metabolism of circulating catecholamines by the liver is unlikely to be impaired after liver transplantation.