The ultrastructure of adrenocortical (interrenal) cells of normal and ACTH-treated chick embryos.

The ultrastructural features of the interrenal cells have been studied in 20-days-old chick embryos following the administration of adrenocorticotropin (ACTH), on the 8th or 15th day of incubation. The interrenal cells of normal embryos contain more SER than RER, mitochondria with tubular cristae, lipid droplets and Golgi complex. Adjacent cells had numerous regions of pentalaminar fusion and intermediate junctions. Neither a precise organization of medullary tissue in relation to interrenal tissue nor any structural differences between interrenal cells were found. Changes in the fine structure of the interrenal cells following ACTH treatment were extensive. The organelles that are known to be involved in the biosynthesis of steroids displayed structural modifications. These were mainly SER, mitochondria, and lipid droplets. Changes were also noticeable in the Golgi complexes, membrane-bound dense bodies (especially in 15 days treated embryos). These results indicate the well developed organelles in the interrenal cells of 20-days-old embryos, and their capacity to respond to ACTH stimulation as early as the 8th day of embryogenesis.