The biphasic effect of organic cations on the excretion of other organic cations.

The renal excretion of 14C-choline or 14C-acetylcholine was increased by the infusion of another organic cation at low rates but was decreased by infusion of the same added organic cation at higher rates with the Sperber technique in hens. The range of low rates of infusion was from 1 X 10(-15) to 1 X 10(-8) mol/min. At infusion rates greater than 1 X 10(-8) mol/min, inhibition of tubular excretion was found. At the low infusion rates, thiamine, lysine, quinine, atropine, acetylcholine and methylguanidine were found to increase 14C-choline excretion. The same compounds with the exception of lysine and acetylcholine inhibited 14C-choline excretion at the higher infusion rates. A biphasic effect on 14C-acetylcholine excretion was also observed with added atropine, thiamine and choline over the same infusion range. Increases in 14C-choline excretion occurred during a choline infusion rate that normally produced an excretory tubular maximum for choline whereas increases in 14C-acetylcholine excretion occurred during infusion of tracer amounts of 14C-acetylcholine. The effect of the addition of organic cations was selective for cations since the tubular excretion of organic anions was not affected by the addition of organic cations. The tubular excretion ratio of 14C-thiamine/p-aminohippuric acid increased from 0.25 to 0.95 when the infusion rate of added unlabeled thiamine was increased from 1 X 10(-11) to 1 X 10(-8) mol/min. Enhanced tubular excretion of 14C-thiamine may represent the effect of the increased load of unlabeled thiamine to protect the labeled thiamine from conversion to a nontransportable metabolite. Enhancement of excretion of 14C-choline and 14C-acetyocholine produced by very small amounts of other organic cations may represent either inhibition of tubular reabsorptive transport or induction of tubular excretory transport.