Subcellular membrane fatty acids of rat heart after cold acclimation or thyroxine.

Relative percent changes in fatty acid (FA) composition of heart mitochondria and microsomes from 30-day-warm-acclimated and cold-acclimated rats were determined by gas chromatography. Rats in both environmental groups received thyroxine (T4) (1 mg/kg per day) or propylthiouracil (PTU) (5 mg/rat per day) for 10 days prior to sacrifice. Mitochondrial total unsaturated fatty acids (TUFA) decreased in cold-acclimated rats relative to warm-acclimated controls but not in cold-acclimated animals receiving PTU. In mitochondria of the T4-treated warm-acclimated group, the relative content of linoleate decreased and that of stearate increased. Heart microsomes from warm-acclimated rats receiving T4 showed large increases in the percentage content of palmitate and stearate accompanied by reductions in linoleate and arachidonate. In cold-acclimated control rats, the relative content of stearate was elevated in both membrane fractions. The results suggested that thyroid hormones may decrease the TUFA composition of heart subcellular membranes by a relative increase in percent stearic acid and decrease in percent linoleic acid. Similar FA changes in these membranes in cold-acclimated rats may be related to the action of thyroid hormones.