Studies of tyramine transfer and metabolism using an in vitro intestinal preparation

The duodenal transfer and metabolism of [3H]tyramine from sacs and perfused segments of rat intestine were determined. In sacs, a linear relationship between the steady-state transfer rate of total tritium and the initial mucosal tyramine concentration was observed, suggesting that the clearance is the same at different concentrations. In duodenal perfusions, there was no significant difference in the amount of total tritium removed between control and everted tissues, whether the flow was 0.2 or 2.0 mL/min. The percentage of [3H]tyramine extracted from the gut lumen depended on the flow rate. About 30-40% of the extracted drug was metabolized; this value decreased to 20% when the rats were pretreated with pargyline. The data support the idea that the transfer mechanism for tyramine is simple diffusion.