The effects of exogenous cortisone acetate on development (especially skeletal development) and on circulating levels of corticosteroids in chick embryos.

Chick embryos were treated with cortisone acetate on day 8 of incubation and the subsequent growth of the whole embryo and the development of the tibia studied to day 18 of incubation. Cortisone, at 10 ng to 2 mg/embryo decreased general body growth; above 0.5 mg/embryo it also retarded morphogenesis by as much as 3 Hamilton-Hamburger stages; and above 1 mg/embryo gross abnormalities were produced. The growth and differentiation of the tibia were affected to a greater extent than was the whole body. The reductions in tibial and total body weight were not linearly related to dose of cortisone injected. The exogenous cortisone acetate resulted in drastic alterations in the circulating levels of cortisone, cortisol, corticosterone, and progesterone, but plasma progesterone level was most readily correlated with the growth retardation. This study emphasizes that avian embryos can readily compensate for exogenous corticosteroids and that caution must be exercised when attributing causality to the substance administered.