Effect of hypothyroidism on glucose transport and metabolism in rat small intestine.

The effect of experimental hypothyroidism on the absorption, transmural transport and metabolism of glucose was studied by perfusion of isolated loops of rat jejunum in vitro. When expressed on a dry weight basis, the rate of absorption was enhanced by 32% (P < 0.01); when expressed on a length basis there was no significant change, since the enhancement per unit weight was almost exactly compensated by a diminution in mass per unit length in the hypothyroid state. When expressed in either units, there was a significant enhancement in transmural transport (+123% and +77%, respectively, both P < 0.001), which reflected in part a diminution in the rate of glucose utilization (-29%, P < 0.01 and -43%, P < 0.001, respectively). The changes in glucose utilization were matched by changes in lactate production. Three factors contributed to the diminution in glucose utilization in the hypothyroid state: a diminution in the concentration of 6-phosphofructo-1-kinase (-35%, P < 0.05), and increase in the S0.5 of 6-phosphofructo-1-kinase for fructose 6-phosphate from 0.4 to 0.6 mM and a fall in the mucosal concentration of fructose 2,6-bisphosphate (-56%, P < 0.05). From the point of view of the whole animal, there is little if any change in the capacity of the intestine to absorb glucose from the lumen, but there is a large enhancement of transmural transport that is metabolically driven.