The effect of triamcinolone on the development of the bursa of Fabricius in chick embryos.

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 differentiation 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.