The effects of intraperitoneal injections of triiodothyronine (0.03, 0.30, 3.0 5/day) on hepatic glucokinase and glucose-6-phosphatase activities were tested in juvenile and adult mice. In hyperthyroid mice glucokinase activity increased above controls and glucose-6-phosphatase activity decreased slightly below controls. By comparing phosphorylating activity (glucokinase) to dephosphorylating activity (glucose-6-phosphatase), it was found that hyperthyroid mice had greater hepatic glucose phosphorylating activity than euthyroid mice. This may indicate a greater capacity for glucose utilization than production. The hepatic enzyme responses to triiodothyronine (T3) in juveniles were greater than in adults. Results were interpreted in relation to the calorigenic action of thyroid hormone. T3 effects were also related to effects of other hormones on blood glucose availability and utilization and to probable ontogenetic changes in hepatic glucose metabolism. (Endocrinology87: 124, 1970) ALTHOUGH the thyroid hormone is ubiquitous in vertebrate animals, its precise mode of action is still unresolved.
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Sheldon Winnick (1970) studied this question.