A sensitive method for the biological assay of secretin and substances with "secretin-like" activity in tissues and biological fluids.

The isolated perfused pancreas is extremely sensitive to secretin and can be used to assay very small quantities of secretin. The addition of theophylline to the perfusate increases the sensitivity of the preparation 4 to 10 fold so that in a good preparation as little a 0.001 C.U. may be detected. Secretin-like activity was detected in biopsy samples of jejunal mucosa taken perorally from man, in the blood of some patients suffering from a profuse watery diarrhoea, and in a metastatic tumour obtained from one such patient. It was also observed that 1 clinical unit of secretin was equal to 4.4 Crick, Harper, Raper units.