RESUMEN
Papaverine in vitro in the concentration of 10 minus power 4 M had no effect on the release of PHA from rat kidney slices at 28? C, when the medium was changed every 30 sec during the 10 min of the experiment : the rate constant of the slow component of the run-out in the control experiments was equal to 0.1441 min minus power 1, lthat of the papaverine treated series equaled to 0. 1674 min minus power 1. In using 5 min intervals for transferring instead of 30 sec the rate constant of the papaverine-free series was significantly lower than that of the papaverine-treated one : 0.091 min minus power 1 versus 0.0731 min minus power 1. There exists a direct relationship between the lost amount of PAH during the 30 sec intervals and actual total PAH-concentration of the kidney slices. Papaverine has no effect on the run-out of PAH at 28? C, because at this temperature the PAH-release is due to processes not requiring energy. At the same time papaverine blocks the reaccumulation of the released PAH. Papaverine affects the in vitro movement of PAH in the kidney slices by inhibiting the uptake of PAH.