The transport of D-glucose, L-glucose and D-mannose across the isolated guinea pig placenta.

Studies were carried out on the transport of 3H-D-glucose, 14C-L-glucose and 3H-D-mannose across the isolated artificially perfused guinea pig placenta and the inhibition of these transports by phloretin was investigated. 1. In 10 out of 13 placentas the transfer of D-glucose exceeds that of L-glucose. 2. In 10 out of 13 placentas the transfer of D-mannose exceeds that of L-glucose. 3. Phloretin (1 times 10 minus 3 M/1) decreases the transport of D-glucose and of D-mannose, it does not decrease the transport of L-glucose. The inhibition is not complete. The characterization of the washing-out curves permits the assumption that some placentas (6 out of 21) cannot discriminate between D- and L-hexoses, because a non specific transfer (simple diffusion) covers the specific one.