The effect of thyrotrophin on oxidative activity in thyroid follicle cells

Abstract

Biochemical evidence, based on supra-physiological concentrations of thyrotrophin (TSH), has indicated that this hormone increases the NADP concentration in thyroid follicle cells. The hormone is believed to act both to enhance the reoxidation of the reduced coenzyme and to generate NADP from NAD. The latter effect, mediated by NAD-+-kinase, could be a major control mechanism in thyroid metabolism. In the present study increased sensitivity has been obtained by the use of maintenance culture and of microdensitometry for measuring enzyme activity in the follicle cells. Using low physiological (0.1 muU/ml), and sub-physiological concentrations of the hormone as are used in the cytochemical bioassay systems, it has been shown that the rate of reoxidation of NADPH is enhanced by TSH. Moreover the NAD-+-kinase activity is also greatly increased, and shows a direct relationship to the concentration of the hormone acting on the segments of the gland in vitro. It is possible that this phenomenon could be used to assay TSH. The results indicate that NAD-+-kinase activity may play a significant part in the control of pentose-shunt oxidation in thyroid follicle cells.

Flow Cytometric Assay of Cytochemically Demonstrated NAD(P)H Oxidoreductase (Diaphorase) Activities

“…For histochemical demonstration of DT-diaphorase activity, the tetrazolium salts NBT and TNBT were usually used as indicators and the reduced co-enzymes were directly added to generate a one-step reaction (e.g., Macha et al 1975;Scherer-Singler et al 1983). Direct measurement is possible providing that the reducibility of the tetrazolium salts is higher than that of CTC (unpublished results) and NT (Seidler 1991), the tetrazolium salt used by Macha et al (1975) in their coupled reaction procedure.…”

“…Direct measurement is possible providing that the reducibility of the tetrazolium salts is higher than that of CTC (unpublished results) and NT (Seidler 1991), the tetrazolium salt used by Macha et al (1975) in their coupled reaction procedure. The lesser reducibility of CTC in comparison to NBT favors its enzymatic reduction, thus preventing nonspecific reactions (Seidler 1991).…”