Effects of Cold Exposure, Thyroid Extract, Methylthiouracil and Dehydroepiandrosterone on Glucose 6-Phosphate and 6-Phosphogluconate Dehydrogenases in Rat Liver and Erythrocytes

Abstract

Liver glucose 6-phosphate dehydrogenase (G6PD) was enhanced in adult male rats exposed to cold (+5°C) for 24 days. A similar effect on G6PD was obtained by a thyroid extract (Thyreoidin Spofa) if administered for 3 weeks. Methylthiouracil (Alkiron Spofa) given for an equal period decreased the activity of 6-phosphogluconate dehydrogenase (6PGD), while the reduction of G6PD was statistically nonsignificant. Two hours after administration, dehydroepiandrosterone (DHEA) in a single i.p. dose of 200 mg/kg exerted a pronounced inhibition of G6PD; 2 hours later the inhibition was no longer apparent. In similar experiments, dehydroepiandrosterone sulphate (DHEA-S) produced, after a single dose (280 mg/kg) a less pronounced fall which was, however, present throughout 4 hours consecutive to DHEA-S application. The activity of 6PGD remained unaffected by the free steroid or by its sulphate.

In vitro a noncompetitive inhibition of liver G6PD by DHEA was observed. The effect of DHEA-S was about 100 times less. None of the tested factors had an effect on rat erythrocyte G6PD or 6PGD.

Key words

Glucose 6-Phosphate Dehydrogenase Activity - Cold Exposure - 6-Phosphogluconate Dehydrogenase Activity - Dehydroepiandrosterone - Thyroid Extracts - Strumigens - Methylthiouracil