Acute Stimulation of Thyroidal NAD⁺Kinase, NADPH Reoxidation, and Peroxidase Activities by Physiological Concentrations of Thyroid Stimulating Hormone Acting in Vitro: A Quantitative Cytochemical Study*

Abstract

Quantitative cytochemical techniques have been employed in a study of some of the acute effects of low doses (0.01----1 mU/liter) of TSH on the metabolism of guinea pig thyroid segments maintained in nonproliferative organ culture. The enzymes involved in the synthesis of NADP+ (NAD+ kinase), its reduction by the pentose-shunt (glucose 6-phosphate dehydrogenase), and its reoxidation both by the microsomal electron chain (diaphorase activity) and by participation in other cellular processes, have been examined. The effect of TSH on peroxidase activity has also been studied. After 10 min stimulation with TSH (1 mU/liter) there was a 60% increase in NAD+ kinase activity which preceded changes in the microsomal reoxidation of NADPH (up 33% by 30 min). There were no changes in the activity of glucose 6-phosphate dehydrogenase. There was a sustained rise in peroxidase activity which reached 129% over control after 30 min. This is the first in vitro demonstration of an acute stimulation of peroxidase and kinase activities by physiological concentrations of TSH. NADPH reoxidation after stimulation with TSH was such that the ratio of NADPH reoxidized via the microsomal respiratory pathway (diaphorase, hydrogen pathway 1) relative to that available for cytosolic utilization (hydrogen pathway 2) increased compared to the unstimulated controls. We suggest that increased NADP+ production (via NAD+ kinase activity) and the preferential shuttling of the NADPH for reoxidation via the microsomal respiratory pathway, coupled with greatly stimulated peroxidase activity, may be important regulators of the control of thyroglobulin iodination and hence thyroid hormone production.

The power to reduce: pyridine nucleotides – small molecules with a multitude of functions

“…In human neutrophils, the activation of NADK by calcium and calmodulin, and the ensuing increase of the NADP content [134] are probably related to cellular activation in response to bacterial challenges, which includes superoxide production by NADPH oxidase. A similar 'oxidative burst' was reported for thyroid cells [147] and for the calcium-mediated defence response in plants [148]. So far, the molecular mechanism of the calcium/calmodulin-dependent activation of NADKs has remained unknown.…”

Activation of the thyroid peroxidase gene in human thyroid cells: effect of thyrotrophin, forskolin and phorbol ester

“…We have shown recently, using primary cultures of human thyroid cells, that the thyroglobulin gene is regu¬ lated at the transcriptional level by TSH (Kung, Collison, Banga & McGregor, 1988). However, the effect of TSH on regulating the TPO gene and its relationship with activation of the thyroglobulin have not been studied previously, although it is clear that TSH modulates the levels of peroxidase activity both in vivo in rats (Nagasaka & Hidaka, 1980) and in vitro in primary cultures of dog thyroid cells (Magnusson & Rapoport, 1985) and on guinea-pig thyroid segments (Perrild, Loveridge, Reades & Robertson, 1988). The recent cloning of the human and porcine TPO genes (Kimura, Kotani, McBride et al 1987;Libert, Ruel, Ludgate et al 1987;Mag¬ nusson, Chazenbalk, Gestautas et al 1987) has al¬ lowed the measurement of alterations in cytoplasmic TPO mRNA levels in primary cultures of dog thy¬ roid cells using a porcine TPO cDNA probe (Chaz¬ enbalk, .…”