Quantification of angiotensin iontophoresis

A method of value for studying the effects of angiotensin II (AII) and angiotensin III (AIII) on the brain is microiontophoresis combined with single unit recording. The purpose of this study was to quantitate the release of angiotensins under various experimental conditions thus providing a firm basis for the iontophoretic application of angiotensins. Quantification of release was accomplished by adding the appropriate [3H]angiotensin to 1 X 10(-3) M solutions of AII and AIII and then measuring the counts released from the tip of the microiontophoretic pipette in vitro into a small volume of Ringer solution. Although both AII and AIII were released by diffusion from micropipettes, this release could all but be eliminated with a retaining current of 20 nA. The release of AII and AIII was linear with respect to the amount of ejecting current applied up to 60 nA, the highest current examined. Angiotensin II at pH 4.5 and AIII at pH 3.5 were released at similar rates of 41.5 and 45.1 fmol/min/nA respectively. Raising the pH of the AII solution to 4.5 reduced the rate of release to 17.9 fmol/min/nA. Transport numbers were determined as follows: AII pH 3.5-0.115; AII pH 4.5-0.035, and AIII pH 4.5-0.145. It can be concluded that angiotensins are readily released by microiontophoresis, the response is linear with respect to application current, and that with the use of the appropriate pH the rate of release of AII and AIII are comparable.