Onset of the response to chorionic gonadotropin in the chick embryo testis

The stage of development of the chick embryo testis when it begins to respond to gonadotropin stimulation was investigated. The testosterone secretion in vitro, measured by radioimmunoassay, was employed to evaluate the response to hCG in testis from 8 to 16 days of incubation. At 8 to 10 days of the chick embryo development, the testis secreted testosterone, but no increment in the steroid production has been observed after hCG treatment. On the contrary, at 12, 14, and 16 days a clear increase in testosterone secretion has been demonstrated when hCG was added to the culture medium. The absence of hCG response before 12 days of incubation agrees with the hypothesis of an early independence period between testis and adenohypophysis during embryonic development.