High-performance liquid chromatographic analysis with diode-array detection of bradykinin, neuropeptide K, and substance P in human plasma.

A method is described for the determination of bradykinin, neuropeptide K (NPK), and substance P in patients with atypical carcinoid syndrome. The developed method uses a combination of conventional and solid-phase extraction as well as high-performance liquid chromatographic techniques. A narrow-bore C18 column with ultraviolet detection is used (200 nm). The technique recovers bradykinin at a level of 98%, NPK at 96%, and substance P at 98% (when pure standards are dissolved) at concentration levels relevant to the atypical carcinoid syndrome. In biological samples, the recovery rate of bradykinin, NPK, and substance P drops to 88, 86, and 88% respectively. The overall analysis time is 150 min from receipt of samples. This method proves to be a valuable tool in the identification of neuropeptides and thus the diagnosis of atypical carcinoid syndrome, especially in puzzling cases with nonspecific symptoms.