Fatty-acid desaturation and microsomal lipid fatty-acid composition in experimental hyperthyroidism

Abstract

The influence of experimental hyperthyroidism in the rat on the synthesis of unsaturated fatty acids and on liver microsomal lipid fatty-acid composition was studied. Triiodothyronine treatment (25 .mu.g/100 g body wt) daily for 3 wk caused no significant changes in .DELTA.9 (stearate) desaturation but a 24% decrease in .DELTA.6 (linoleate) desaturation. Much larger doses of triiodothyronine increased .DELTA.9 desaturation. Liver microsomal fatty-acid composition in hyperthyroidism is altered with significantly increased proportions of stearate and arachidonate and decreased proportions of palmitate, palmitoleate, linoleate (C18:2) and eicosa-8,11,14-trienoate (C20:3). These changes, other than the decreased proportion of C20:3 fatty acid, which may be due to the diminished .DELTA.6 desaturase activity, cannot be attributed to changes in fatty-acid desaturation. Most of these changes were due not simply to the decreased weight gain or the increased food intake of the hyperthyroid animals. Only the decreased C18:2 fatty-acid proportions could be mimicked by restricting food intake of control animals and none of the changes were prevented by restricting food intake of hyperthyroid animals. Most of the changes in microsomal lipid fatty-acid composition are likely to be due to a thyroid hormone effect on peripheral lipid mobilization or lipid degradation.