Insulin and insulin-like growth factors/somatomedins in fetal and neonatal development.

In this presentation we have attempted to review the status of knowledge of the hormonal regulation of fetal and neonatal growth, and have placed particular emphasis on the roles of insulin and somatomedin in fetal growth. The inaccessibility of the fetus and the physical and ethical constraints on study of its growth have resulted in slow progress. Furthermore, the opportunity for the fetus to benefit from homologous hormones from a variety of sources has made it difficult to assess the effect of withdrawal of individual hormones. Many of the advances made have resulted from attempts to determine hormone concentrations in fetal blood, identify hormone binding by fetal tissues, and examine the effects of natural or experimentally induced deviations in hormone availability. In the future, attention should be focused on developing study models which better isolate the fetus from the influence of multiple, homologous hormones. Progress should also come as the result of more detailed study of the influence of individual growth factors on in vitro growth of fetal cells and tissues, assessment of control mechanisms for growth factors in the fetus, and experiments directed at recognizing the complex interactions between individual growth factors and between growth factors and hormones.