The Effect of Extrathyroidal Conversion Inhibitor from Food-Deprived Animals on Iodothyronines Deiodination by Pituitary and Cerebral Cortical Homogenates in Vitro

Summary

The influence of an inhibitor of iodothyronines' extrathyroidal conversion on T₄, T₃ and rT₃ deiodination by adult pig pituitary and cerebral cortical homogenates has been investigated. The homogenates were incubated with T₄, T₃ and rT₃ in the presence of 5 mM dithiotreitol and evaporated diethyl ether extracts of sera obtained from fed and starved (1-14 days) rabbits. The extracts had no influence either on T₄ to T₃ or on T₄ to rT₃ conversion in cerebral cortex. Deiodination of rT₃ to 3,3'-T₂ in that tissue was significantly inhibited only by the extracts of sera obtained from 4 days starved rabbits. Inner-ring deiodination of both rT₃ and T₃ was not changed by the extracts got from short-term (1-4 days) fasted animals but was significantly reduced by the extracts from long-term (7-14 days) food-deprived subjects. Pituitary conversion of T₄ to T₃ was diminished by 35% in the presence of sera extracts gained from 1-9 days fasted rabbits and by about 50% on day 14 of fasting, but only the latter change was statistically significant. Short-term fasting inhibited T₄ to rT₃ conversion on days 2 and 4. Both deiodinations of rT₃ and 5-deiodination of T₃ were affected by extracts of sera collected during long-term fasting.

Extrathyroidal Conversion Inhibitor (IEC) - Thyroid Hormones Deiodination - Diethyl Ether Sera Extracts - Starvation - Pituitary - Cerebral Cortex