INFLUENCE OF HYPOTHYROID STATE ON CARDIAC SARCOLEMMAL INCORPORATION OF DIETARY OMEGA-6 AND OMEGA-3-FATTY-ACIDS

Diets enriched in either omega-6 or long-chain omega-3 fatty acids wer e fed to euthyroid and hypothyroid weanling rats. Feeding euthyroid an imals the omega-3 diet significantly reduced the omega-6/omega-3 ratio in all phospholipids from cardiac sarcolemma, except sphingomyelin, r elative to omega-6-fed animals. The content of 20:4 omega 6 was reduce d in all phospholipid classes in omega-3-fed animals indicating a supp ression of Delta(6)- and Delta(5)-desaturase activity. Membrane levels of 20:5 omega 3, 22:5 omega 3 and 22:6 omega 3 were higher in omega-3 -fed animals with the result that the total omega-3 content of all pho spholipid classes was increased several-fold, again except in sphingom yelin. Four weeks after the induction of hypothyroidism the omega-6/om ega-3 ratio was not different from euthyroid animals, regardless of di et. However, the 20:4/18:2 ratio was lowered even more indicating a fu rther decrement in Delta(6)- and Delta(5)-desaturase activity. The inc orporation of dietary long-chain omega-3 fatty acids into sarcolemmal phospholipids was not affected by the hypothyroid state. The data sugg ests that in growing rats thyroid status determines the influence diet ary fatty acids have on cardiac sarcolemmal phospholipid fatty acid co mpositions, primarily through effects on incorporation and metabolism of omega-6 and omega-3 fatty acids. These changes have the potential t o modulate the activities of membrane functions associated with myocar dial performance.