The effect of triamcinolone on the development of the bursa of fabricius in chick embryos

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Abstract
Triamcinolone acetonide (TAC), a long‐acting synthetic glucocorticoid, markedly reduces survival rates in chick embryos when injected in small (10–100 ng) single‐injection doses on days 5 or 9 of incubation. In addition to its embryotoxic effect, TAC causes such gross malformations as gastroschisis, reduced body weight, encephalocele, micrognathia, curled toes, and club feathers. These effects of TAC are more severe in 5‐day‐old chick embryos than in 9‐day‐old ones. A comparison with cortisol (hydrocortisone), a structurally similar, naturally occurring steroid, indicates that TAC is approximately 600 times more toxic in chick embryos than cortisol. TAC also inhibits differentation of the bursa of Fabricius: single injections on the chorioallantoic membrane (CAM) of 10–20 ng on day 5 or 9 reduced size and weight of this lymphoid organ. Histological examination showed a sharp reduction in the size and number of bursal follicles, a reduction in the number of lymphocytes within these follicles, and a degeneration of the epithelium covering bursal plicae.