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A study of the mechanism of transport of benzylpenicillin in the rat submaxillary gland.

In vitro studies performed on slices of rat submaxillary gland to evaluate uptake and efflux of 14C-benzylpenicillin (10(-6)M, 10(-5)M) showed that uptake of 14C-benzylpenicillin was not significantly altered by aeration with N2, addition of 10(-5)M CN- or 10(-3) M probenecid, or substitution of K2SO4 in place of NaCl in the KRT buffer to produce a depolarizing solution. Lowering the extracellular pH (pHe) resulted in increases rates of uptake and efflux, whereas increasing the pHe resulted in decreased rates. The in vivo uptake of penicillin into whole glands excised from rates treated in vivo was very similar to that seen in the slice preparation. However, addition of probenecid to salivary gland slices in vitro decreased the rate of effux. These data suggest that the movement of penicillin in the rat salivary gland may occur by a two-step mechanism: (1) passive exchange of penicillin into the gland dependent on the degree of dissociation of penicillin, and (2) active excretion of the drug from the gland by a transport mechanism similar to that of the kidney densitive to probenecid.