Growth factors and the regulation of pre- and postnatal growth

Peptide growth factors represent a largely paracrine level of intercellular communication that is basic to the process of life. Growth factors are present in the ovum and are amongst the first products expressed by the embryonic genome. They function as both signals and progression factors for embryonic tissue growth, induction, differentiation, maturation and function. While a widespread tissue expression is demonstrable during fetal development, and in certain postnatal tissues such as the epiphyseal growth plate, growth factor presence in the adult is restricted to tissues sharing rapid cellular turnover such as ovary. However, a transient re-expression of peptide growth factors occurs during adult tissue repair. In addition to mitogenic peptides such as IGFs or EGF, the family of growth factors also includes physiological growth inhibitors such as TGF beta and certain neuropeptides. Insulin is mitogenic in the early embryo and evidence is presented to support a continuation of this role, under defined nutritional conditions, in late gestation. The importance of insulin to pre- and postnatal growth has prompted an expanding literature dealing with the interactions of nutrients, hormones and growth factors during the growth and functional maturation of the islets of Langerhans. While the expression of growth factors in the early embryo is apparently autonomous, some, such as IGFs, become increasingly dependent on nutrient, insulin and GH availability during fetal development and in childhood growth. This has resulted in circulating IGF I and II determinations becoming useful diagnostic markers of endocrine-based growth disorder and nitrogen balance.