T. Mochizuki

Dose-response comparisons of canine plasma gastroenteropancreatic hormone responses to bombesin and the porcine gastrin-releasing peptide (GRP)

The effect on plasma gastroenteropancreatic hormone levels on infusing the porcine gastrin-releasing peptide and bombesin into dogs demonstrated no qualitative difference in the spectrum of activity of the two peptides. Sustained elevation in plasma immunoreactive gastrin, pancreatic polypeptide, enteroglucagon, gastric inhibitory polypeptide, pancreatic glucagon and transient elevations in plasma insulin were seen during infusions of both peptides. The similar spectrum of activities and the structural homology between the two peptides suggests that the porcine gastrin releasing peptide is the porcine counterpart of the amphibian peptide bombesin.

Urinary concentrating defect in rats given Shiga toxin: elevation in urinary AQP2 level associated with polyuria

Shiga toxin (Stx) plays a central role in the etiology of hemolytic uremic syndrome (HUS) associated with Stx-producing Escherichia coli infection. The deposition of Stx2 in the renal collecting duct epithelial cells of rats administered Stx2 intravenously has been demonstrated by immunohistochemistry, and these rats were shown to develop substantial morphological changes in the kidney tubules, associated with polyuria. Severe polyuria was observed as an early event with no other obvious sequelae after Stx administration, in parallel with elevated urinary level of aquaporin 2 (AQP2) water channel protein that was determined by a sandwich EIA assay. Immunoblotting revealed that Stx treatment markedly induced an elevation in urinary AQP2 level and reduction in AQP2 protein in the renal plasma membranes. Elevated urinary AQP2 level was a more sensitive marker to assess Stx-induced renal tubular damage than urinary beta2-microglobulin or N-acetyl-beta-D-glucosaminidase in rats. Stx2 caused more severe renal tubular impairment than Stx1. Change in urinary AQP2 level by Stx1 and Stx2 at non-lethal doses of 40 ng/kg and 10 ng/kg, respectively, was reversed at 7 days in association with recovery of urinary concentrating ability, suggesting that there is a causative link.

Is helodermin-like immunoreactivity in human thyroid C cells due to a salmon calcitonin-like substance?

Helodermin-like and salmon calcitonin (sCT)-like immunoreactivities co-existed in a subset of human calcitonin (hCT)-containing cells in normal human thyroid tissue and medullary thyroid carcinomas. Helodermin/sCT-immunoreactive cells were mostly different from calcitonin gene-related peptide (CGRP)-positive cells. Helodermin and sCT immunoreactivities were not identified in pulmonary and pancreatic hCT-positive neuroendocrine tumors, except for a few lung tumor cells showing positive staining with one of two sCT antisera used. Helodermin immunoreactivity demonstrated by rabbit antiserum R0086 was completely abolished in the presence of synthetic sCT, while sCT immunoreactivity was not absorbed by synthetic helodermin. The carboxyl terminal Arg30-Thr31 sequence (and Pro35 amide structure) of helodermin would be the epitopic site recognized by this antiserum, since a similar amino acid sequence is present in sCT molecules but absent from hCT and CGRP.

Demonstration of two distinct insulin-binding components in solubilized human placental membranes by radioimmunoassay using synthetic peptide and anti-synthetic peptide antibody

A peptide corresponding to the 957-980 sequence of human placental insulin receptor precursor (HIRP) was synthesized and antisera were produced against the synthetic peptide. Anti-synthetic HIRP(957-980) serum HIR-27 was proved to cross-react with HIRP-related proteins in solubilized human placental membranes. A radioimmunoassay developed with the antiserum and synthetic peptide HIRP(957-980) enabled us to separate, in combination with gel filtration, two insulin-binding components in solubilized human placental membranes which conceivably correspond to the alpha 2 beta 2 and alpha beta structures of the placental insulin receptor. The two components were shown to be distinct in insulin-binding behavior depending on conditions of pH and ionic strength in the binding assay.