Autoradiography of pituitary cells stimulated by castration or methimazole feeding.

It has been argued that the increase in size of the pituitary of castrated cockerels is due to hypertrophy of gonadotropic cells, some of which have been converted from other pituitary basophils. A counter argument could maintain that new gonadotropes are recruited from chromophobes that are replaced by mitotic division of undifferentiated cells. Since mitosis requires thymine for DNA replication, labelled thymine (H3-thymidine) incorporated in DNA identifies new cell formation. On this basis, the chicken pituitary does not produce enough new cells to account for the size differences associated with castration or methimazole treatment.