Failure of D- and L-Thyroxine to Protect Cholesterol and Oil Fed Cockerels Against Coronary Atherogenesis

Abstract

In cockerels, L-thyroxine was significantly more active biologically than an equivalent dose of D-thyroxine, or even four times the dose, as demonstrated by the effects on body weights, organ weights and comb index. In cockerels fed an atherogenic diet, the plasma cholesterol concentrations in all the thyroxine-treated groups were significantly lower than in the control groups. No consistent effect of D-thyroxine on thoracic aorta atherosclerosis was observed. However, L-thyroxine had some protective action in the one experiment done. Despite suppression of hypercholester-olemia, no protection against coronary atherosclerosis was seen with the administration of either L- or D-thyroxine. In fact, with an increase in dose of D-thyroxine to 4 mg, there developed actually an increase in the percentage of coronary vessels showing atherosclerosis. These observations confirm once again the importance of avoiding reliance exclusively on blood cholesterol levels when judging the effects of hormones on atherogenesis.