Glucocorticoid effects on the embryonic chick heart. I. Glucocorticoid enlargement of the heart

Cortisol increases the heart weight relative to body weight following injection of growth suppressing amounts of the hormone on incubation days 9, 10, 13, and 15. Hormone administration increases glycogen, glycosaminoglycan (GAG), and total lipid concentration in the embryonic myocardium. Deoxyribonucleic acid (DNA) and protein concentration are decreased proportionally. Glycogen synthetase and radiosulphate incorporation into GAG are increased by the glucocorticoid. Lack of growth inhibition of the embryonic myocardium by glucocorticoids is not due to absence of glucocorticoid receptors. [3H]-Dexamethasone was shown to bind to a cytoplasmic and nuclear fraction of the chick heart. Binding to a cytoplasmic protein could be demonstrated in the heart at nine days of embryonic development and increased with developmental age. The increase in cardiac mass appears to be specific for the glucocorticoid hormones when compared with epinephrine and deoxycorticosterone. The latter two hormones did not increase cardiac mass.