Effect of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on steroid concentrations in blood and gonads of chicken embryo.

The aim of the present study was to examine the effect of TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) injected at the early stage of incubation on hormonal activity of the chicken ovary and testis during the second half of embryogenesis measured by steroid concentrations in blood plasma and gonads. The effect of TCDD on hatchability was also evaluated. In the first experiment TCDD was administrated to chicken eggs on day 7 of embryogenesis (E7) at doses of 0 (control), 2.5, 5 and 10ng/egg dissolved in 50μl of peanut oil. Blood plasma for estradiol (E2) and testosterone (T) determination was collected from embryos at E14, E18, E20 and at hatching (D1). In the second experiment TCDD at doses of 0 (control), 2.5, 5 and 10ng/egg dissolved in 50μl of DMSO was injected on E6. Blood plasma and gonads were collected on the day of hatching for progesterone (P4), T and E2 concentrations measured by means of the RIA method. It was found that TCDD injection: (1) increased the level of T and decreased the level of E2 in the plasma of female chicken embryos during the second half of embryogenesis, while on the other hand in male embryos the effect of TCDD was opposite, (2) increased T and E2 concentrations in plasma of newly hatched female chickens with a concomitant decrease of these hormones in the ovary; P4 in the ovary was elevated by TCDD, (3) decreased P4 and T in plasma and testes, whereas increased E2 concentration in the plasma of newly hatched male embryos (E2 concentration in the testes was below the sensitivity of the applied RIA method), and (4) decreased hatchability at all examined doses. The results obtained clearly demonstrate that exposure to TCDD at an early stage of embryogenesis affects steroid production and secretion by chicken gonads. The effect of TCDD depends on (1) the applied dose, (2) the day of embryogenesis, and (3) the sex. It is suggested that dioxins are potent modulators of the process of steroidogenesis in the chicken gonads. Moreover, the data obtained indicate that dioxins exert an effect on embryo development and the hatching process.