Expression of insulin-like growth factor I in transgenic mice with elevated levels of growth hormone is correlated with growth

Endocrinology. 1988 Jul;123(1):433-7. doi: 10.1210/endo-123-1-433.


To study the role of insulin-like growth factor I (IGF-I) in mediating the growth-promoting function of GH, IGF-I expression was assayed in transgenic mice carrying either GH or GRF fusion genes. These mice exhibit enhanced growth as a result of high level ectopic expression of GH and have 2-fold elevation of both hepatic IGF-I mRNA levels and circulating IGF-I levels. Hepatic IGF-I mRNA levels are low at birth regardless of GH levels; they increase approximately 10-fold during postnatal development and become GH inducible 2 weeks after birth. The ontogeny of circulating IGF-I is similar. Accelerated growth in transgenic mice with GH fusion genes commences 3 weeks after birth despite high circulating GH levels at least as early as birth. In addition, endogenous mouse GH-secreting somatotroph cells in the pituitary are present in normal numbers at 3 weeks, but are undetectable 4 weeks after birth. Because the time at which IGF-I expression becomes GH responsive slightly precedes both the initiation of accelerated growth and the time when endogenous GH disappears, we conclude that IGF-I is directly involved in mediating the GH signal and that delayed induction of IGF-I gene expression is responsible, at least in part, for the delayed onset of other GH-responsive events.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Aging
  • Animals
  • Cloning, Molecular
  • Genes
  • Growth Hormone / genetics*
  • Insulin-Like Growth Factor I / genetics*
  • Liver / growth & development*
  • Metallothionein / genetics
  • Mice
  • Mice, Transgenic / growth & development*
  • Pituitary Gland / growth & development*
  • Promoter Regions, Genetic
  • RNA, Messenger / genetics
  • Reference Values
  • Somatomedins / genetics*
  • Transcription, Genetic


  • RNA, Messenger
  • Somatomedins
  • Insulin-Like Growth Factor I
  • Growth Hormone
  • Metallothionein