ABSTRACT
Hormones and peptide growth factors are important regulatory substances present in metazoan organisms. They represent biological signals involved in the regulation of cell growth and differentiation as well as in the control of specific metabolic processes during both pre- and postnatal life. Certain hormones and peptide growth factors act in a restricted manner on specific types of cells, whereas others may have a broad, perhaps universal, spectrum of activity for different types of cells and tissues.
