Effect of cold exposure on rat erythrocyte membrane-bound acetylcholinesterase. Role of thyrotropin in the thyroid hormones interplay.

The influence of cold exposure at 4 degrees C for different periods of time (from 12 h to 42 days) on the allosteric inhibition by F- of the rat erythrocyte membrane-bound acetylcholinesterase from rat fed a corn oil diet was studied. The cold exposure decreased the values of the Hill coefficient n from 1.6 to 1.0. When the cold-exposed rat was transferred from the cold environment to 23 degrees C, the values of n reached the control values. The factors that play in the allosteric desensitization phenomenon were characterized as L-triiodothyronine, L-thyroxine, and thyrotropin. The relationship betwen changes in the values of n and physiological concentrations of thyroid hormones and thyrotropin in cold-exposed rat is shown. Thyrotropin showed a facilitatory action on the blocking action of thyroxine on the triiodothyronine effect. The intravenous injection of thyrotropin-releasing hormone (TRH) yields confirmatory results for this regulatory mechanism since the values of n for acetylcholinesterase shifted as predicted.