Glucocorticoid-induced alterations in the rabbit heart

Daily intramuscular injection of the synthetic glucocorticoid, betamethasone, into rabbits for 2 weeks resulted in both gross and microscopic alteration of cardiac muscle. A 30% increase in heart weight was based on increased muscle fiber size occasioned by the deposition of fibrillogranular material (not glycogen in nature) in the cytosol. At the same time, some myocytes underwent profound myolysis, predominantly at the nuclear poles, occasionally pervading the entire cell. Conventional lysosomes were not increased in number or size, but certain cells possessed prominent cytoplasmic vacuoles that sometimes contained mitochondria. The biochemical basis for these cardiac changes is undetermined, but the obvious ultrastructural damage produced by betamethasone, particularly dissolution of myofibrils, may prove to have clinical significance.