Studies of the fate of tyramine in dogs: the effect of monoamine oxidase inhibition, portafemoral shunt and coronary artery ligation on the kinetics of tyramine.

Radioimmunoassay of tyramine (T) was used to investigate the kinetics of T in plasma of three groups of dogs (control, pretreated with monoamine oxidase inhibitor and those with portafemoral shunt). Furthermore, the influence of coronary artery ligation on the T content of the heart was studied. After i.v. administration of T-HCl (1.7mumol/kg, 0.3 mg/kg), there was a rapid initial decline in T plasma levels with an average T 1/2 of 4.3 minutes. Similar results were obtained in experiments in which the same dose of T-3H was used. There was a 10-fold difference between 3H and T concentrations. Pretreatment with a monoamine oxidase inhibitor resulted in a decrease in T metabolism as reflected by changes in pharmacokinetic parameters (estimated area under the curve AUC, 8166 vs. 1000 ng x min x ml-1, P less than .001; total body clearance, BC, 35.7 vs. 285 ml/min/kg. P less than .005). Similar results were obtained in dogs with portafemoral shunt. Coronary artery ligation resulted in an increase in the level of T in the infarction [1.2. +/- 0.3 (S.E.M.) ng/ml] compared to those of adult volunteers.