Immunoreactive neuromedin B and neuromedin C: distribution and molecular heterogeneity in rat and human tissue extracts.

Immunoreactive neuromedin B and neuromedin C were characterized and measured in rat and human tissue extracts, using radioimmunoassay combined with gel filtration and high performance liquid chromatography in order to clarify tissue distribution and molecular structure. There are two distinct systems of bombesin-like peptide found in rat and human tissue. The neuromedin B family, including neuromedin B and big neuromedin B, is a major bombesin-like peptide in the brain; the neuromedin C gastrin-releasing peptide family is found mainly in the alimentary tract. Neuromedin B is the major and big neuromedin B the minor constituent of central nervous neuromedin B immunoreactivity. Gastrointestinal neuromedin C immunoreactivity is composed chiefly of neuromedin C in rats, and two N-terminally extended forms of neuromedin C including gastrin-releasing peptide in man. It is probable that molecular heterogeneity reflects species variation.