The first radioimmunoassay was described by Yalow & Berson in 1960, since when the technique has been widely used in physiological and patho-physiological studies of the protein hormones. The success in this field has led to a number of attempts to develop similar assays for the small peptide hormones (molecular weight less than 3000). However, these compounds present certain difficulties which have considerably retarded progress. The purpose of the present review is to discuss the problems of the radioimmunoassay of the neurohypophysial peptides, with particular reference to oxytocin and vasopressin.
The problems of the radioimmunoassay of small peptide hormones
There are two major problems. (1) Being of low molecular weight (about 1000) they are poor immunogens. As a result, the preparation of high-affinity antisera is considerably more exacting than in the case of larger molecules. (2) Their levels in the circulation are, in molar terms, considerably lower than those of