Failure of D- and L-thyroxine to protect cholesterol and oil fed cockerels against coronary atherogenesis

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.

Influence of various dietary fats on hypercholesterolemia and atherogenesis in cockerels

When cockerels were given a cholesterol supplemented, fat-free, semi-synthetic diet as the basic ration, all oils and solid fats were atherogenic and caused elevated serum cholesterol levels. The degree of hypercholesterolemia and atherogenesis was related to fatty acid composition of the fat fed. Margarines were less atherogenic and less hypercholesterolemic than oils. The additives used in the preparation of margarine have some influence on maintaining lower cholesterol levels, but do not appear to have any significant effects on atherogenesis. The structural isomers formed during margarine manufacture may be responsible through an alteration of lipid metabolism.

Benefit from testosterone and hydrocortisone on coronary atherogenesis in cockerels on a low protein atherogenic diet

In the presence of high fat and high cholesterol in the diet, growing cockerels showed more marked hypercholesterolemia and atherosclerosis when their protein intake was low. Testosterone counteracted both the increased hypercholesterolemic and the enhanced atherogenic effects of a low protein diet. Hydrocortisone markedly aggravated the hypercholesterolemia in these cockerels but offered significant protection against coronary atherogenesis when associated with a low protein intake. When the dietary protein level is adequate neither testosterone nor hydrocortisone lowered coronary atherogenesis, despite modification of plasma cholesterol levels. Protein level in the diet must be considered in evaluating hormonal atherogenic effects.