Carrier-mediated uptake of hexoses by the rat visceral yolk sac.

The rat visceral yolk sac is shown to possess a sodium-independent, phloretin-sensitive, and phlorizin- and ouabain-insensitive transport system for hexoses. The rate of uptake of (3H)2-deoxy-D-glucose was measured in vitro and shown to be greatest on the 12th day, decreasing progressively with increasing gestational age up to the 20th day. Little uptake of 3-O-methyl-D-glucose, alpha-methylglucoside or L-glucose occurred. On uptake by the visceral yolk sac, 2-deoxy-D-glucose was phosphorylated, leading to considerable accumulation of this sugar. Several sugars inhibited 2-deoxy-D-glucose uptake as follows: D-glucose = mannose greater than fructose greater than galactose greater than xylose greater than fucose.