Pituitary and extrapituitary growth hormone: Pit-1 dependence?

Growth hormone (GH) is primarily produced in pituitary somatotrophs. The synthesis of this hormone is thought to be dependent upon a pituitary-specific transcription factor (Pit-1). However, many extrapituitary tissues are now known to express GH genes. The extrapituitary production of GH may therefore indicate an extrapituitary distribution of the Pit-1 gene. The extrapituitary production of GH may, alternatively, indicate that GH expression occurs independently of Pit-1 in extrapituitary tissues. These possibilities are considered in this brief review.