Deiodinase Activity in the Rat Thyroid when the Organic Binding was Blocked by Excess Iodine

Ochi, Yukio; Yokota, Kazuhisa; Marumoto, Susumu

doi:10.1507/endocrine1927.41.7_804

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“…This observation is in contrast with our results (Table 3) and those of Ochi, Yokota and Marumoto (1965). More recent results obtained in rats and mice (Zarkarija, Bastomsky and McKenzie 1969) and in sheep (Burke 1969) clearly show no signifieant change in NADPH eoncentration 3 hours after TSH stimulation.…”

Section: Discussioncontrasting

confidence: 99%

“…Another possible explanation for the increased release of inorganic iodide from the thyroid a few minutes after the onset of TSH stimulation is an increased cellular concentration of the coenzyme NADPH. Such an assumption seems reasonable because addition of NADPH to thyroid homogenates (Table 1, Maayan and Rosenberg 1963, Ochi, Yokota and Marumoto 1965, Faberova and Knopp 1971 and slices (Table 4, Bastomsky and Rosenberg 1966, Faberova andKnopp 1971) enhances deiodinating activity significantly; an increase of NADPH concentration after in Vivo and in vitro TSH stimulation would therefore become apparent in our system as an increased deiodinating capacity of the unsupplemented homogenates.…”

Section: Discussionmentioning

confidence: 89%

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lodotyrosine Deiodination in the Normal and Acutely TSH-Stimulated Thyroid

Conti¹,

Studer²

1977

Horm Metab Res

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The deiodination of L-MIT-125I was measured in rat thyroid homogenates and slices before and after acute TSH stimulation. Slices and homogenates were incubated with identical concentrations of tissue and substrate in the presence and absence of NADPH. 1 USP unit TSH added in vitro to thyroid slices failed to stimulate deiodination; a single in vivo ip injection of 3 USP units TSH was also unable to raise deiodinating activity. In contrast to TSH, NADPH added to homogenates and slices enhanced deiodination significantly. However, several arguments, including a review of the literature, strongly militate against the hypothesis of an increased intracellular concentration of the coenzyme NADPH being the prerequisite to enhanced deiodination. The results suggest that deiodinase activity in acutely stimulated thyroids is not limited by the intracellular concentration of the enzyme itself nor by the availability of co-enzyme. Therefore, the increased iodide release induced by acute TSH stimulation is a mere consequence of the enhanced thyroglobulin proteolysis and does not require higher enzyme concentration. It will be shown subsequently that a different conclusion must be drawn in experiments with chronic TSH stimulation.

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Section: Discussioncontrasting

confidence: 99%

Section: Discussionmentioning

confidence: 89%