Effect of hyper- and hypothyroidism on phospholipid fatty acid composition and phospholipases activity in sarcolemma of rabbit cardiac muscle.

Lipid content and composition of fatty acids esterified to phospholipids of cardiac sarcolemma isolated from hyperthyroid, hypothyroid and control rabbits were analysed. Hyperthyroidism resulted in a significant reduction of the cholesterol to phospholipid molar ratio as compared to control animals, while hypothyroidism exerted the opposite effect. Complex changes in composition of phospholipid fatty acids observed in hyperthyroid state led to an elevation of the fatty acid unsaturation index over the control value. The unsaturation index value was, however, not affected in the hypothyroid state. Thyroxine hormone administration increased phospholipase A1 and decreased phospholipase A2 activity. The opposite effect was observed in thyreodectomized animals. The effect of changes in sarcolemmal bulk phospholipids upon thyroxine administration or deficiency on regulation of activity of membrane-bound enzymes is discussed.