Thyroid Hormone Administration in Vivo Regulates the Activity of Hepatic Glycogen Phosphorylase Phosphatase*

Abstract
Hort term (48 h) administration in vivo of either T4 or T3, but not the biologically inactive D-isomer of T3, was associated with a decrease in basal glycogen phosphorylase a activity and an increase in phosphorylase a phosphatase activity of rat hepatocytes. This influence of thyroid hormones on hepatic phosphorylase a and phosphorylase phosphatase activities was shown to be dose dependent. As little as 0.0025 mg T3/kg BW administered in vivo at 48, 24, and 3 h before liver excision increased the phosphatase activity by 20%. The administration of 0.25 mg T3/kg BW on the same schedule increased the phosphatase activity by nearly 100%.

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