BACLOFEN (BETA-P-CHLOROPHENYL-GAMMA-AMINOBUTYRIC ACID) TRANSPORT ACROSS RAT JEJUNUM

Intestinal transport of baclofen (beta(p-chlorophenyl)-gamma-aminobuty ric acid) in the rat has been examined in vitro. Influx of baclofen ac ross the brush-border membrane (J(mc)Bacl) and steady-state accumulati on by everted segments of the intestine were measured. J(mc)Bacl could be accounted for as the sum of a saturable process with a maximum rat e of approx. 10-20 nmol cm-2 b-1 and a K1/2Bacl of approx. 0.3 mM and a diffusive contribution with a permeability of 0.073 cm h-1. J(mc)Bac l was Na+- and Cl--independent. The steady state distribution ratio be tween the intracellular space of the everted segments and incubation f luid was 1.0 +/- 0.1 (n = 12). Inhibition tests demonstrated that the Na+- and Cl--independent, passive, but saturable fraction of baclofen transport can not be mediated by any of the known amino acid carriers of the rat small intestine. Preliminary results suggests that qualitat ively baclofen transport in guinea-pig and rabbit is also by facilitat ed transport.