Gut: first published as 10.1136/gut.14.4.284 on 1 April 1973. Downloaded from Gut, 1973, 14, 284-288 Cellular localization of gastric inhibitory polypeptide in the duodenum and jejunum JULIA M. POLAK, S. R. BLOOM', MARION KUZIO, J. C. BROWN, AND A. G. E. PEARSE From the Department ofHistochemistry, Royal Postgraduate Medical School, Hammersmith Hospital, London, and the Department ofPhysiology, University ofBritish Columbia, Vancouver, Canada SUMMARY Indirect immunofluorescence studies using an antiserum to purified porcine gastric inhibitory polypeptide indicate, in the gastrointestinal tract of dog and man, that this polypeptide is present in cells situated predominantly in the mid-zone of the glands in the duodenum and, to a lesser extent, in the jejunum. Absolute correlation of the gastric inhibitory polypeptide cell with one or other of the known endocrine-like cells identified by electron microscopy awaits confirmation by electron immunocytochemistry. It is here identified as an endocrine polypeptide cell of the APUD series and, provisionally, as the D, cell. While the hormonal status of a given polypeptide depends ultimately on physiological experiments the present results strengthen the view that gastric inhibitory polypeptide is indeed a hormone. In 1969 Brown, Pederson, Jorpes, and Mutt described We report here the results of immunofluorescence an enterogastrone, extractable from porcine intestine, studies on the localization of GIP in human and http://gut.bmj.com/ which strongly inhibited gastric acid secretion. The canine intestine. purification of an apparently similar enterogastrone was reported in the same year by Lucien, Itoh, Sun, Material and Methods Meyer, Carlton, and Schally. The first of these poly- peptides, named gastric inhibitory polypeptide Operative samples of duodenal and jejunal mucosa (GIP) by Brown, Mutt, and Pederson (1970), was from seven human subjects were studied. Two of later shown, with the publication of the complete these had gastric carcinoma with very low gastric on October 2, 2021 by guest. Protected copyright. sequence by Brown and Dryburgh (1971), to contain acid levels. 43 amino acid residues. Similarities in its structure to Canine antral, duodenal, and jejunal mucosa both porcine glucagon and porcine secretin were samples were obtained from two mongrel puppies, noted. Fifteen of the first 26 amino acids occur as in 8 and 12 weeks old respectively. the former and nine of the first 26 are in the same In both species small pieces of mucosa were position as in secretin. The 17 C-terminal residues processed in a variety of different ways, as indicated are not common to any other intestinal polypeptide. below. The cellular localization of only two of the poly- peptide hormones of the intestine has so far been I MMUNOFLUORESCENCE recorded. These are secretin, found in the S cell of Three processing schedules were employed. the duodenum by Bussolati, Capella, Solcia, Vassallo, 1 Fixation in cold 4 % methanol-free formaldehyde and Vezzadini (1971) and, independently, by Polak, for periods between three hours and five days (Polak, Bloom, Coulling, and Pearse (1971a), and entero- Bussolati, and Pearse, 1971). After washing out glucagon which was located in the L cell of the excess fixative part of the tissue was quenched at intestine by Polak, Bloom, Coulling, and Pearse - 1580 in Arcton (Freon) 22 and subsequently used (1971b). for the provision of cryostat sections. These were picked up on gelatine-formaldehyde-coated slides. 'Present address: Institute of Clinical Research, Middlesex Hospital, The remaining tissues were dehydrated in graded London Wt. alcohols and embedded in paraffin wax. Sections Received for publication 12 January 1973. were allowed to dry, at 370, for 24 to 48 hours. 284 Gut: first published as 10.1136/gut.14.4.284 on 1 April 1973. Downloaded from Cellular localization ofgastric inhibitory polypeptide in the duodenum andjejunum 285 2 Fixation in 10% carbodiimide (Kendall, Polak, mineral acid (0.2N HCI, 60° for 30 minutes to two and Pearse, 1971): this fixative is prepared by hours); by the lead haematoxylin method (Solcia, dissolving, immediately before use, 1-ethyl-3(3-di- Capella, and Vassallo, 1969); by the xanthydrol methylaminopropyl)-carbodiimide hydrochloride method for tryptophan and 5-hydroxytryptamine (Sigma) in 0d1M phosphate buffer saline at pH 7.1. (Lillie, 1957); the Masson-Fontana method for Tissues were fixed for three hours and then washed in enterochromaffin granules (Pearse, 1972); and the several changes of 0dlM phosphate buffer (pH 7.1), silver impregnation technique of Grimelius (1968). containing 75 % sucrose, for at least 24 hours. As after methanol-free formaldehyde, both cryostat and ELECTRON MICROSCOPY paraffin sections were employed. Small blocks of tissue were fixed, immediately after 3 Selected pieces of mucosa were quenched removal, in 3% glutaraldehyde in 0.1M phosphate immediately after removal in Arcton (Freon) 22 at buffer at pH 7.6 for two hours at 4°. Excess fixative - 1580. Some of these were used for the preparation was removed by repeated washing in 0dIM phosphate of unfixed cryostat sections, others were freeze-dried buffer containing 01M sucrose. They were then for 12 to 18 hours at -40° in a thermoelectric dryer. dehydrated in ethanol and ethoxypropane and Subsequently these pieces were embedded in vacuo finally embedded in Araldite mixture. With some in 56° paraffin wax. Sections (5 ,um) were mounted blocks, a double fixation procedure was carried out, on glycerine-albumin-coated slides and dried at 370 using postfixation with osmium tetroxide at 40 for for 24 to 48 hours. two hours (Millonig, 1962). Sections were stained by Sections processed by each of these schedules were lead citrate and uranyl acetate and viewed in an used for an indirect immunofluorescence procedure AEI EM 6B electron microscope. (Coons, Leduc, and Connolly, 1955). Control sections were invariably employed, as described by Results Polak et al (1971a and b), in order to check the specificity of the immune reactions. The antibodies Immunofluorescence studies showed that GIP cells used were raised in guinea-pigs against a highly were relatively numerous by comparison with the purified GIP and fluorescein-labelled rabbit anti- number of S (secretin) cells found in identical areas guinea-pig globulin was obtained commercially of the intestine. They were localized predominantly (Hyland). in the middle zone of the glands, in the duodenum, http://gut.bmj.com/ Fluorescence microscopy was carried out using and to a lesser extent in the jejunum, in both dog and a Zeiss (Oberkochen) standard universal microscope man (figs 1 and 2). There were a few GIP cells in the with HB0200 lamp, BG12 and BG38 excitation filters, and a K530 barrier filter (50% transmission at about 530 nm). Photomicrographs were taken on Ilford FP4 film. on October 2, 2021 by guest. Protected copyright. DARK-FIELD OBSERVATIONS Fresh frozen cryostat, or freeze-dried paraffin sections, were studied for dark-field luminescence, which reveals pancreatic A cells (Cavallero and Solcia, 1964) and intestinal enteroglucagon cells (Polak et al, 1971b). CYTOCHEMICAL AND STAINING REACTIONS Small pieces of tissue from each region were fixed for 24 hours in the following fixatives: 6% glutar- aldehyde in 0.1M phosphate buffer pH 7.4; Bouin's fluid; glutaraldehyde-picric acid (Solcia, Vassallo, and Capella, 1968). All samples were washed in 560 water, dehydrated, cleared, and embedded in Fig. 1 Indirect immunofluorescence reaction using paraffin wax. Sections (5 gm) from appropriately guinea-pig antiporcine GIP serum andfluorescein- fixed blocks were processed by methods selective for labelled sheep anti-guinea pig IgG. Dog duodenum. In the secretory granules of gastrointestinal endocrine this longitudinal section (MFF-fixed) through the cells. duodenal glands a single GIP cell is visible. Its granules Sections were stained with 1 % aqueous toluidine are concentrated on the site of the cell adjacent to the blue at pH 5 0, with and without treatment with basement membrane. x 750 Gut: first published as 10.1136/gut.14.4.284 on 1 April 1973. Downloaded from 286 Julia M. Polak, S. R. Bloom, Marion Kuzio, J. C. Brown and A. G. E. Pearse Fig. 2 As figure 1. Human duodenum. Transverse section. Shows a single basigranular GIP cell. x 450 duodenal villi, but not in the jejunal villi. Human GIP cells were most easily found in duodenal samples from the two cases with low gastric acidity, and least easily found in cases of duodenal ulcer. Cytochemical and staining reactions distinguish a number of endocrine cell types in the gastro- intestinal tract. The GIP cell was characterized as Fig. 4 Electron micrograph, human duodenum: a http://gut.bmj.com/ lead haematoxylin-positive, Grimelius-positive, non- single D1 cell containing smallgranules ofvariable argentaffin and weakly positive for tryptophan. It electron density, without visible halo. x 5500 on October 2, 2021 by guest. Protected copyright. ~~~~~ ~~~~~~~ ~~~Fig. 3 Electron micrograph, cells and two as I (intermediate) cells. x 4000 1.1k Gut: first published as 10.1136/gut.14.4.284 on 1 April 1973. Downloaded from Cellular localization ofgastric inhibitory polypeptide in the duodenum andjejunum 287 was considered to belong to the APUD series of (secretin) and the L cell (enteroglucagon). They endocrine polypeptide cells (Pearse, 1969) although therefore support the proposition that GIP is a true its remaining APUD characteristics have not yet hormone. been determined. In the glands of duodenum and jejunum electron We would like to thank our clinical colleagues, and microscopy likewise revealed a number of different especially Professor R. B. Welbourn, for the pro- -types of endocrine cell (fig 3). In the first part of the vision of surgical material from their cases, and we duodenum, the predominant site for immuno- are grateful for skilled technical assistance provided fluorescent GIP cells, the cell whose distribution by Miss C. M. Heath (EM) and Mrs B. Salas. The most closely matched the latter was the small work was supported by a grant from the Wellcome granule-containing D1 cell (fig 4) described by Trust.