Iontophoretic release of adrenaline, noradrenaline and 5-hydroxytryptamine from micropipettes.

Estimations have been made of the amounts of adrenaline, noradrenaline and 5-hydroxytryptamine released by iontophoresis from micropipettes. In most experiments, the amount released was linearly related to the total electrical charge, but the transport numbers for different pipettes, filled with samples of the same solutions of adrenaline or of noradrenaline, varied substantially. Two pipettes containing noradrenaline failed to release any appreciable amounts of the drug. The transport number of 5-hydroxytryptamine was relatively constant (mean, 0.14).