Thyroxine Treatment and Chicken ( Gallus gallus ) Embryo Duodenum in vitro

To study direct action of thyroxine (T 4 ) on duodenal development in chicken embryos, duodena from stage 42 White Leghorn (strain Hyline 934F) Gallus gallus embryos were cultured, cut into quarter segments and slit open on grids. L‐T 4 was added to McCoy's 5A medium to concentrations of 14 ng/ml or 14 ng/100 ml. To control for possible physicochemical effects, D‐T 4 was added to other media in the same concentrations, and saline vehicle was added to control media. Bovine serum albumin (BSA) was added to a duplicate set of cultures (0.2% w/vol) as a nutritive supplement. After 48 h alkaline phosphatase (E.C. 3.1.3.1) specific activity was significantly elevated ( p < 0.05) in segments cultured with 14 ng L‐T 4 /100 ml (non‐BSA) compared to saline control cultures. With 14 ng L‐T 4 /ml (BSA) phosphatase activity had increased significantly compared to segments treated with 14 ng L‐T 4 /100 ml (BSA), while those cultured with D‐T 4 (BSA) had significantly lower activities than all other BSA‐treated groups including controls. Total protein content was significantly elevated in all D‐T 4 treated segments, both non‐BSA and BSA‐treated, compared to protein values of all other treatment groups. Following 48 h of culture the fine structure of epithelial mucosal cells usually showed condensed cytoplasm, while goblet cells were well developed, structural features appearing in all segments regardless of treatment. The responses after treatment further support a direct role for T 4 in duodenal development.