Thyroxine treatments in vivo and ultrastructural differentiation of chicken (Gallus gallus) embryo duodenum

Abstract

Previously, L-thyroxine (L-T4) treatment of 16.5-day-old chicken embryos (approximately stage 42) correlated with a precocious increase in prehatching duodenal alkaline phosphatase specific activity. This paper examines the effects of similar L-T4 treatment on ultrastructural differentiation of the absorptive epithelium. White Leghorn embryos (strain Hyline 934F of Gallus gallus) were given 0.1 mL of saline containing 5-μg doses of either L-T4, or D-T4, or saline vehicle alone through windows in the shell. Untreated windowed and intact unwindowed embryos were additional controls. At the time of treatment (16.5 days) and 24, 48, and 72 h later embryos were killed and their duodena were fixed. At least three embryos were examined in each group. Twenty-four hours after treatment stage 43 epithelial cells resembled stage 42 cells. Forty-eight and 72 h following L-T4 treatment stage 44 and 45 embryos showed evidence of increased Golgi and lysosome activity but depletion of lipid droplets and glycogen stores. Control treatments with D-T4 or saline vehicle did not appear to affect epithelial cell ultrastructure as these embryos resembled unwindowed and windowed control embryos at all stages.