Growth-promoting effects of endothelin-1 and endothelin-3 on chick embryos

Chick embryos were treated with single or multiple doses of 0-250 pmol of endothelin-1 (ET-1) or endothelin-3 (ET-3) and their effects on development were examined in embryos ranging from 7 to 14 days in age. The overall sizes of the head, trunk, beak or wings were increased (5-14%) in ET-treated embryos. Additionally, the lengths or widths of the telencephalic or optic lobes and the diencephalon in the embryonic brains were also increased (4-14%). These effects were observed when the embryos were treated with ET for three consecutive days beginning on day 2 of incubation or from day 1-5. Similar results were obtained by a single injection given on the 5th day of incubation, but not on day 1 or 3. Morphological studies suggested that ET-1 and ET-3 promoted maturation rather than non-specific growth in size. Histological studies revealed that ET-treated brain tissues were more cellular and organized in appearance than control brains. There was no increased incidence of vascular abnormalities or structural malformations subsequent to ET-treatment. These results suggest that ET has growth factor-like effects and that treatment on and around the 5th day of incubation seemed to be most effective for the early phase in brain development in chick embryos.