Evidence for the Presence of Somatostatin 28 in Plasma

Somatostatin-like immunoreactivity (SLI) from dog and rat plasma eluted from Biogel P-6 columns as three distinct peaks. A large-molecular-weight peak was present in the void volume of the column, an intermediate-sized peak (SLI²⁸) coeluted with synthetic somatostatin 28 (S-28), and a small-molecular-weight peak (SLI¹⁴) coeluted with SRIF. Material from the SLI²⁸ peak diluted in parallel to the S-28 standard in the radioimmunoassay and behaved identically to S-28 on high pressure liquid chromatography (HPLC). Levels of SLI²⁸ in the portal vein were consistently > the simultaneously measured peripheral levels (portal peripheral ratio 2.2 ± 0.2). Venous samples drawn from multiple sites suggested that SLI²⁸ is segregated by the duodenum and/or pancreas and the intestine. This data is consistent with the possibility that S-28 is a hormone distinct from SRIF.