Development of an insulin-sensitive glucose transport system in chick embryo hearts

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Abstract
Glucose uptake, sorbitol space, and total water content were measured in chick embryo hearts at various stages of development, in control aerobic and anaerobic conditions and after the addition of insulin, 2,4-dinitrophenol (DNP), or ouabain to the incubation medium. In 5-day-old hearts, glucose uptake is relatively high; sorbitol distributes itself rapidly in a volume of about 90 ml/ 100 g of fresh tissue; insulin, DNP, and ouabain have no effect on glucose uptake, sorbitol space, or tissue water; anoxia increases glucose uptake, but has no effect on sorbitol space or tissue water. In 7-day-old hearts, glucose uptake and sorbitol diffusion are slower and sorbitol space reaches values of about 90 ml/100 g of fresh tissue only after 2 hr of incubation. In 10-day-old hearts, glucose uptake is still lower; sorbitol space remains below 50 ml/100 g of fresh tissue; insulin, DNP, anoxia, and ouabain cause significant increases in glucose uptake, but do not modify sorbitol space or tissue water. These results are consistent with the hypothesis that the 5-day-old chick embryo heart is freely permeable to glucose and to sorbitol and that a "membrane" capable of regulating the transport of glucose appears between the 7th and 10th day of embryonic development. No evidence of stimulation of glucose phosphorylation by insulin, DNP, or ouabain was obtained.