Deltins: immunochemical evidence for a novel population of peptides of the D cells of the gastro-entero-pancreatic endocrine system.

Differences between the immunocytochemical behaviour of antisera to partially purified porcine gastrins and antisera to either synthetic human gastrin-17-I or highly purified porcine gastrin-17-I raised the hypothesis that hog antral gastrin extracts contain peptides different from somatostatin and gastrin that are responsible for the immunocytochemical reaction of the former antisera in the D (delta) cells of the gastro-entero-pancreatic (GEP) endocrine system. This study was performed to prove this hypothesis. A discard fraction obtained after gel filtration of hog antral gastrin extracts on Sephadex G-50 Superfine was employed to immunize five rabbits. The discard fraction is highly heterogeneous on two-dimensional electrophoresis and contains merely traces of somatostatin and gastrin in RIA. However, rabbit antisera to the discard fraction give strongly positive immunocytochemical reactions exclusively in the D cells of the human antroduodenal mucosa and of the pancreatic islets. Absorption of the antisera with the lyophilized discard fraction abolishes the staining of the D cells, whereas absorption of the antisera with several somatostatins does not affect the staining. Vice versa, staining of the D cells with antisera to cyclic somatostatin-14 is abolished by absorption of the antisera with somatostatin-14 but not by absorption with excess of the discard fraction. In RIA, antisera to the discard fraction do not bind radiolabelled (Tyr(1))-somatostatin-14, Tyr-somatostatin-28 or synthetic human gastrin-17-I. Two-dimensional electrophoresis of acid extracts of isolated canine pancreatic islets followed by Western blotting shows different patterns of distribution of immunoreactive spots obtained with antisera to the discard fraction, to somatostatin-14, and to human proinsulin respectively. These results indicate the existence of a novel population of peptides of the D cells of the GEP endocrine system, for which we propose the term deltins.

Immunoradiometric and luminescence immunoenzymometric assay of human thyrotropin from dried blood spots for screening of neonatal hypothyroidism.

Two monoclonal antibodies to thyrotropin prepared in our laboratory were employed for the development of two-site immunometric assays in two modifications for the estimation of human thyrotropin in dried blood spots designed for the screening of neonatal hypothyroidism. The immunoradiometric assay using the second antibody labelled with 125I is simple and fast (one incubation step lasting 2 h). The detection limit of 1 mU/l and the absence of the hook effect up to a concentration of more than 1000 mU/l are optimal for neonatal screening; the presence of other glycoprotein hormones does not interfere with the assay. In the luminescence immunoenzymometric assay the second antibody is labelled with peroxidase. In spite of the two-step configuration the method is fast (4.5 h) and enables specific determination of thyrotropin levels in the range of 2.4-1100 mU/l. The conditions and properties of both immunometric assays described are comparable with the time-resolved immunofluorometric assay widely used in Europe.