Immunocytochemical localization of glucagonlike and gastric inhibitory polypeptidelike peptides in the pancreatic islets and gastrointestinal tract

Abstract

The distribution of cells displaying glucagonlike or gastric inhibitory polypeptide (GIP)-like immunoreactivity was examined in the pancreatic islets and gastrointestinal tracts of rats, dogs, and humans. A-cells in the pancreatic islets in all three species were stained by antisera having regional specificity for pancreatic-type glucagon, gut-type glucagon (glicentin), or GIP. Oxyntic A-cells of the gastric mucosa in dogs and humans also were stained comparably by these three antisera. In contrast, the K- and L-cells in the intestinal mucosa of those species were stained only by antisera capable of reacting with GIP or gut-type glucagon, respectively. Tests of antibody specificity showed that the GIP antiserum did not cross-react with either pancreatic- or gut-type glucagon. Likewise, the glucagon antisera showed no cross-reactivity with GIP. Hence, these findings suggest that pancreatic and gastric A-cells contain a peptide with GIP-like immunoreactivity distinct from glucagon or glicentin per se. Although the exact basis of th GIP-like immunostaining of A-cells is unknown, it may be due to the presence of a glucagon precursor sharing certain amino-acid sequences with GIP. This hypothesis is consistent with several recent investigations showing that the processing of proglucagon molecules differs between the A- and L-cells.

Immunohistochemical distribution of glucose‐dependent insulinotropic polypeptide in the adult rat brain

“…Studies concerning GIP immunoreactivity in A‐cells of pancreatic islets have been questioned because of the use of different antibodies with varying specificity (Smith et al,1977; Alumets et al,1978; Ahren et al,1981; Sjolund et al,1983; Smith,1983). It has been shown that members of the secretin‐glucagon family have a similar amino acid sequence near the N‐terminal part of the cDNA that encodes the active peptide (Kopin et al,1990) but are otherwise different.…”

New Views on the Identification of the Various Cell Types in the Pancreatic Islets of the Rat

“…1979;Unger and Orci, 1981;Orci. 1982;Smith, 1983]. If the A cells were in cluded in the same category as the B cells, owing to the similarities of their secretory granules, without taking into account the granule sizes and the other cytological characteristics, the islets of both the dorsal and the ven tral lobe would be lacking in one of the cell types other wise identified with immunohistochemical methods, and the relative percentages of the various cell types would be absolutely mistaken.…”

Immunochemical Studies of an Insulin-like Material in the Parotid Gland of Diabetic BB Rats

“…4 Under normal conditions, this peptide might be converted to an insulin-like molecule by enzymatic systems common to both islet B-cells and salivary cells; 115 but, when affected by diabetogenic agents, IDCs might not properly cleave this precursor molecule, causing it to resist chemical extraction without necessarily influencing its immunostaining. 7 Insulin is secreted in the saliva of both animals and humans, 451314 and our results provide histologic evidence on the origin of salivary insulin-like material. Because salivary glands have been implicated as a potential source of circulating insulin, 41316 it seems reasonable to speculate that our findings of insulinlike immunoreactivity in parotid IDCs of two types of diabetic animals may help explain the so-called "honeymoon phase" of insulin secretion in human IDDM.…”