412 THYPDID REGULATION OF PHOSPHOENOLPYRUVATE CARBOXYKINASE IN THE PERINATAL PERIOD OP THE RAT

Abstract

Triiodothyronine (T₃) is known to induce gluconeogenesis in the liver of adult rats. Hence we enquired whether it could be involved in the steep rise of phosphoenolpyruvate carboxykinase (PEPcK) activity described for the newborn. Two injections of T₃ (20 μg/100 g body weight each) to the mother rat on days 20 and 21 of pregnancy resulted in a ten to 50-fold rise in PEPcK activity in fetal liver. At the sane time the relatively high activity in brown fat was decreased by about 50%. T₃ levels in the fetuses of injected mothers were 42.75 ± 2.25 ng/ml, compared to 27.3 ± 1.8 in the control fetuses. In suckling rats 24 hours after a single injection of 50μg/100 g body weight essentially the same effects in both tissues were observed. At that time blood levels of insulin and glucagon were found to be elevated. These results are very similar to those described previously for corticosteroids (Endocrinol. 103: 1417-1424, 1978). However, T₃ does not lead to a rise in fatty acid synthetase activity in brown fat, while prednisolone does. Thus the mechanisms of action of the two hormones are probably not the same. Our data indicate that T₃ may be involved in the neonatal rise in hepatic PEPcK activity.

(Supported by B.C. Heart Foundation).

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