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Plasma concentrations of 17β-estradiol (E2) and left ovarian histology were investigated by light and electron microscopy in female Japanese quail from Day 10 of embryonic development through Day 7, posthatch. Plasma E2 levels remained relatively constant (102 to 140 pg/mL) in the embryo followed by a sharp decrease posthatch (47 to 70 pg/mL).
Beginning on Day 10 of incubation, cells in the medullary portion (medullary cell; MC) of the left ovaries exhibited ultrastructural evidence of steroidogenic capability. The MC had numerous lipid droplets in close proximity to the smooth endoplasmic reticulum (SER). Mitochondria were also observed in the vicinity of the lipid droplets and SER. On Days 10 and 12, the cristae of the inner mitochondrial membranes were of a lamellar configuration; the cristae of some mitochondria in MC had a tubular appearance by Day 14. These data document relative ontogenic changes in ovarian morphology and plasma E2 levels during the early developmental period in female Japanese quail. These data further support the role of this steroid in sexual differentiation.