Immunofluorescent localization of secretin in the canine duodenum

CD36-dependent signaling mediates fatty acid-induced gut release of secretin and cholecystokinin

Genetic variants in the fatty acid (FA) translocase FAT/CD36 associate with abnormal postprandial lipids and influence risk for the metabolic syndrome. CD36 is abundant on apical enterocyte membranes in the proximal small intestine, where it facilitates FA uptake and FA-initiated signaling. We explored whether CD36 signaling influences FA-mediated secretion of cholecystokinin (CCK) and secretin, peptides released by enteroendocrine cells (EECs) in the duodenum/jejunum, which regulate events important for fat digestion and homeostasis. CD36 was immunodetected on apical membranes of secretin- and CCK-positive EECs and colocalized with cytosolic granules. Intragastric lipid administration to CD36 mice released less secretin (-60%) and CCK (-50%) compared with wild-type mice. Likewise, diminished secretin and CCK responses to FA were observed with CD36 intestinal segments in vitro, arguing against influence of alterations in fat absorption. Signaling mechanisms underlying peptide release were examined in STC-1 cells stably expressing human CD36 or a signaling-impaired mutant (CD36K/A). FA stimulation of cells expressing CD36 (vs. vector or CD36K/A) released more secretin (3.5- to 4-fold) and CCK (2- to 3-fold), generated more cAMP (2- to 2.5-fold), and enhanced protein kinase A activation. Protein kinase A inhibition (H-89) blunted secretin (80%) but not CCK release, which was reduced (50%) by blocking of calmodulin kinase II (KN-62). Coculture of STC-1 cells with Caco-2 cells stably expressing CD36 did not alter secretin or CCK release, consistent with a minimal effect of adjacent enterocytes. In summary, CD36 is a major mediator of FA-induced release of CCK and secretin. These peptides contribute to the role of CD36 in fat absorption and to its pleiotropic metabolic effects.

CD36-dependent signaling mediates fatty acid-induced gut release of secretin and cholecystokinin

Genetic variants in the fatty acid (FA) translocase FAT/CD36 associate with abnormal postprandial lipids and influence risk for the metabolic syndrome. CD36 is abundant on apical enterocyte membranes in the proximal small intestine, where it facilitates FA uptake and FA-initiated signaling. We explored whether CD36 signaling influences FA-mediated secretion of cholecystokinin (CCK) and secretin, peptides released by enteroendocrine cells (EECs) in the duodenum/jejunum, which regulate events important for fat digestion and homeostasis. CD36 was immunodetected on apical membranes of secretin- and CCK-positive EECs and colocalized with cytosolic granules. Intragastric lipid administration to CD36 mice released less secretin (-60%) and CCK (-50%) compared with wild-type mice. Likewise, diminished secretin and CCK responses to FA were observed with CD36 intestinal segments in vitro, arguing against influence of alterations in fat absorption. Signaling mechanisms underlying peptide release were examined in STC-1 cells stably expressing human CD36 or a signaling-impaired mutant (CD36K/A). FA stimulation of cells expressing CD36 (vs. vector or CD36K/A) released more secretin (3.5- to 4-fold) and CCK (2- to 3-fold), generated more cAMP (2- to 2.5-fold), and enhanced protein kinase A activation. Protein kinase A inhibition (H-89) blunted secretin (80%) but not CCK release, which was reduced (50%) by blocking of calmodulin kinase II (KN-62). Coculture of STC-1 cells with Caco-2 cells stably expressing CD36 did not alter secretin or CCK release, consistent with a minimal effect of adjacent enterocytes. In summary, CD36 is a major mediator of FA-induced release of CCK and secretin. These peptides contribute to the role of CD36 in fat absorption and to its pleiotropic metabolic effects.

Modulation of secretin release by neuropeptides in secretin-producing cells

Nerve fibers containing bombesin (BB)/gastrin-releasing polypeptide (GRP), pituitary adenylate cyclase-activating polypeptide (PACAP), vasoactive intestinal polypeptide (VIP), or galanin are known to innervate the mucosa of the upper small intestine. Both BB/GRP and PACAP have been shown to elicit secretin secretion in vivo. We studied whether the above-mentioned neuropeptides can act directly on secretin-producing cells, including the murine neuroendocrine cell line STC-1 and a secretin cell-enriched preparation isolated from rat upper small intestinal mucosa. Secretin release from both cell types was stimulated by various agents known to elicit secretin release and by the neuropeptides BB, GRP, and PACAP, suggesting a comparable response between the two cell preparations. The effects of neuropeptides were further studied in STC-1 cells. BB, GRP, and PACAP stimulated secretin release time and concentration dependently. VIP also stimulated secretin release concentration dependently. Stimulation by BB/GRP or PACAP was accompanied by elevation of inositol-1,4,5-trisphosphate (IP3) or cAMP, respectively. The stimulatory effect of PACAP on secretin release was synergistically enhanced by BB without any synergistic increase in IP3 or cAMP production, suggesting cross talk between different signal transduction pathways downstream of the production of these two second messengers. The L-type Ca2+ channel blocker diltiazem (10 microM) and the Ca2+ chelator EGTA (1 mM) significantly inhibited BB-stimulated secretin release by 64% and 59%, respectively, and inhibited PACAP-stimulated release by 75% and 55%, respectively. The protein kinase A-specific inhibitor Rp-cAMPS (100 microM) also inhibited both BB- and PACAP-stimulated secretin release by 30% and 62%, respectively. Galanin inhibited BB- and PACAP-stimulated secretin release and production of second messengers in a concentration-dependent and pertussis toxin-sensitive manner. These results suggested that the neuropeptides BB/GRP, PACAP, VIP, and galanin can modulate secretin release in secretin-producing cells and that STC-1 cells can serve as a useful model for studying the cellular mechanism of secretin secretion elicited by luminal secretagogues and neuropeptides.

Two alternative processing pathways for a preprohormone: a bioactive form of secretin

An N-terminally 9-residue elongated form of secretin, secretin-(-9 to 27) amide, was isolated from porcine intestinal tissue and characterized. Current knowledge about peptide processing sites does not allow unambiguous prediction of the signal peptide cleavage site in preprosecretin but suggests cleavage in the region of residues -10 to -14 counted upstream from the N terminus of the hormone. However, the structure of the isolated peptide suggests that the cleavage between the signal peptide and the N-terminal propeptide occurs at the C-terminal side of residue -10. Moreover, the isolated peptide demonstrates that secretin can be fully processed C-terminally prior to the final N-terminal cleavage. The results from this report, and those from earlier studies, where C-terminally elongated variants were isolated, show that the processing of the secretin precursor may proceed by one of two alternative pathways, in which either of the two ends is processed first. The bioactivity of the N-terminally extended peptide on exocrine pancreatic secretion was lower than that of secretin, indicating the importance of the finally processed free N terminus of the hormone for interaction with secretin receptors.

Ultrastructural identification of human secretin cells by the immunogold technique. Their costorage of chromogranin A and serotonin

We have localized secretin in a morphologically distinctive endocrine cell scattered in the epithelium covering the villi and uppermost crypts of the human duodenum and jejunum. The human secretin cell was characterized by relatively large (mean diameter 299 nm +/- 69 SD), fairly irregular granules, the majority of which showed homogeneous distribution of secretin and chromogranin A immunolabelling in a structurally homogeneous core. Other granules had a targetoid pattern due to an inner, argyrophobe, secretin-immunoreactive body surrounded by an argyrophil, chromogranin A immunoreactive mantle. These targetoid granules represent a distinctive ultrastructural marker of the secretin cell. Secretin cell granules have been shown to react with chromogranin A antibodies and Grimelius' silver, while lacking chromogranin B immunoreactivity. About 1/3 of secretin cells also showed serotonin immunostaining.

Conversion of somatostatin-28 to somatostatin-14 during maturation of epithelial cells in the porcine jejunum

Fractions of isolated epithelial cells were harvested from a segment of porcine jejunum by ten successive incubations with a chelating buffer. The cell fractions showed a progressive decrease in the activity of the brush-border enzymes, alkaline phosphatase and sucrase, with increasing incubation number but a progressive increase in the ability to incorporate labelled thymidine into DNA. Fractions enriched in cells from the crypt region (fractions 9 and 10) contained higher concentrations per mg protein of somatostatin-like immunoreactivity (1.8-fold), glucagon-like immunoreactivity (5.3-fold) and serotonin (3.0-fold) than fractions enriched in cells from the villus tip (fractions 1 and 2). Analysis of extracts of the fractions by gel filtration/radioimmunoassay showed that somatostatin-28 represented the predominant molecular form of somatostatin-like immunoreactivity in all cell fractions but the relative proportion of somatostatin-14 (and related metabolites) to somatostatin-28 was significantly higher (P less than 0.05) in fractions enriched in villus cells (fraction 1 and 2) than in fractions enriched in crypt cells (fractions 5-10). This result suggests that metabolism of somatostatin-28 to somatostatin-14 takes place during migration of the D cell from the crypt base to the villus tip. Heterogeneity in the somatostatin-14 region of the chromatograms indicates that the peptide may be further metabolized by the action of aminopeptidases.

Tritiated thymidine radioautographic study on the origin and renewal of secretin cells in the rat duodenum

The origin and renewal of secretin cells in the duodenum were investigated using the unlabeled antibody peroxidase-antiperoxidase technique and radioautography in rats killed at various times after single or multiple injections of [3H]thymidine. Secretin cells were spatially distributed from the upper crypt to the villus tip, being particularly numerous in the upper two-thirds of the duodenal villi. After a single injection of [3H]thymidine, there were no labeled secretin cells, indicating a lack of self-replicating activity. After repeated injections of the isotope, labeled secretin cells appeared and increased in number. They first occurred at the upper part of the crypt and the lower part of the villus, and later at the villus tip. All these cells were found to be labeled after continuous labeling for 120 h, which is considered to be the renewal time for this cell population.

Comparative studies of plasma secretin response after reconstructive surgery of the stomach and pancreas

The postprandial plasma secretin response was examined in ten normal persons, seven patients with a Billroth I and seven with a Billroth II anastomosis after subtotal gastrectomy, seven with a Roux-en-Y anastomosis, two with an interposed jejunal anastomosis, and five with a modified Child's anastomosis after pancreatoduodenectomy. The postprandial plasma secretin response in patients with Billroth I anastomosis was better than that in patients with a Billroth II anastomosis but was less than that of normal subjects. Although no postprandial secretin response was noted in Roux-en-Y anastomosis after total gastrectomy, a response was seen in patients with the interposed jejunal anastomosis because the digested food passed through the duodenum, but it was less than that for Billroth I and II patients and normal controls. After a modified Child's reconstruction, the postprandial secretin response was similar to that of patients with the Billroth II, which preserved the duodenum. A patient with a modified Child's reconstruction was examined 12 years after surgery and had the same response as other patients with the modified Child's reconstruction and those with a Billroth II anastomosis within 2 months after surgery. After ingestion of hydrochloride solution, the plasma secretin release in patients with a Billroth I and II anastomosis after subtotal gastrectomy and Roux-en-Y anastomosis after total gastrectomy had a better response than after a meal, but this was less than in normal subjects. The authors suggest that careful selection of intestine for the gastrointestinal anastomosis, which contains many secretin secretory cells, is important to obtain endogenous secretin release. For gastrojejunostomy after pancreatoduodenectomy, a method preserving the pylorus is better than the usual gastrojejunostomy because it maintains gastric acid. The ingestion of secretin stimulants, such as hydrochloride, may help to prevent pancreatic dysfunction after gastrectomy and other surgical reconstructions.

Ultrastructural localization of secretin in endocrine cells of the dog duodenum by the immunogold technique. Comparison with ultrastructurally characterized S cells of various mammals

Secretin has been localized by the immunogold technique in endocrine cells of the dog duodenum--previously described as "K cells"--characterized by secretory granules with double structure consisting of a secretin-containing osmiophilic core surrounded by an argyrophil halo. Granules resembling those of dog secretin cells were also found in some ultrastructurally characterized S cells of the cat, pig, rat and rabbit duodenum, thus confirming in these species the identification of S cells with secretin cells. Conversely, the cells previously described as "S cells" in the dog lacked secretin immunoreactivity.

Secretin exerts inhibition of the 8BrcAMP-stimulated 86Rb influx into avian red blood cells

Avian erythrocytes possess a Na+ and K+ cotransport system which can be inhibited by loop diuretics. The newly discovered diuretic effect of secretin in man led us to study the effect of this hormone on the cotransport system. Secretin caused a 50% inhibition of the 8BrcAMP-stimulated 86Rb influx into red blood cells from goose at a concentration of 8.5 X 10(-6) M, while furosemide and bumetanide caused a 50% inhibition at concentrations of 7 X 10(-6) M and 9 X 10(-8) M, respectively. It is suggested that the diuretic effect of secretin is mediated through an inhibitory or blocking effect on the Na+ and K+ cotransport system.

Gastro-intestinal and neurohormonal peptides in the alimentary tract and cerebral complex of Ciona intestinalis (Ascidiaceae)

Polypeptide-hormone producing cells were localized in the alimentary tract and cerebral ganglion of Ciona intestinalis using cytochemical, immunocytochemical and electron-microscopical methods. Antisera to the following peptides of vertebrate type were employed: bombesin, human prolactin (hPRL), bovine pancreatic polypeptide (PP), porcine secretin, motilin, vasoactive intestinal polypeptide (VIP), beta-endorphin, leu-enkephalin, met-enkephalin, neurotensin, 5-hydroxytryptamin (5-HT), cholecystokinin (CCK), human growth (GH), ACTH, corticotropin-like intermediate lobe peptide (CLIP) and gastric inhibitory peptide (GIP). Immunoreactive cells were found both in the alimentary tract epithelium and in the cerebral ganglion for bombesin, PP, substance P, somatostatin, secretin and neurotensin. Additionally, in the cerebral ganglion only, there were cells immunoreactive for beta-endorphin, VIP, motilin and human prolactin. 5-HT positive cells, however, were restricted to the alimentary tract. No immunoreactivity was obtained either in the cerebral ganglion or in the alimentary tract with antibodies to leu-enkephalin, met-enkephalin, CCK, growth hormone, ACTH, CLIP and GIP. Prolactin-immunoreactive and pancreatic polypeptide-immunoreactive cells were argyrophilic with the Grimelius' stain and were found in neighbouring positions in the cerebral ganglion. At the ultrastructural level five differently granulated cell types were distinguished in the cerebral ganglion. Granules were present in the perikarya as well as in axons. The possible functions of the peptides as neurohormones, neuroregulators and neuromodulators are discussed.

Secretin immunoreactivity in rat and pig brain

Secretin immunoreactivity in rat and pig brain has been identified and characterized utilizing a highly specific radioimmunoassay and fractionation on a high pressure liquid chromatographic system reverse phase column. One immunoreactive peak from each brain extract was observed. Secretin immunoreactivity from rat brain and duodenum coelute, but eluted slightly ahead of the immunoreactivity from pig brain and duodenum and from synthetic porcine secretin. Immunoreactive secretin is widely distributed in the thalamus, hypothalamus and olfactory bulb, cerebral cortex, midbrain, septum, striatum, hippocampus, medulla and pons. The highest concentrations occur in the pineal and the pituitary gland.

Stimulation of bile and pancreatic secretion by duodenal perfusion with Na-taurocholate in the cat compared with jejunal and ileal perfusion

In the anesthetized cat duodenal perfusion with Na-taurocholate (TC, 0.2 M, pH 6.1, 290 mosmol, 45 ml x h-1) stimulated pancreatic volume (0 to 326 +/- 236 mg x 10 min-1) and bicarbonate secretion (0 to 34.2 +/- 4.1 mumol x 10 min-1), whereas pancreatic enzyme output was sparse. Simultaneously with the pancreatic response, bile flow increased from 139 +/- 74 mg to 484 +/- 146 mg x 15 min-1 (p < 0.05). During perfusion of the upper jejunum both pancreatic and biliary responses were significantly lower than the responses to duodenal TC perfusion (p < 0.05). During TC perfusion of the terminal ileum there was no response from the pancreas, whereas the increase in bile flow accounted only for an increase in the bile-acid-dependent fraction. The concomitant stimulation of both the hydrokinetic function of the pancreas and the bile-acid-independent bile flow might be mediated by a release of secretin.

A cytochemical and immunofluorescence study of endocrine cells in the gut of the ascidian Styela clava

Strong secretin-like immunofluorescence has been demonstrated in endocrine-like cells from the gastric epithelium of Styela. These cells also stain with lead haematoxylin and exhibit a brilliant formaldehyde-induced fluorescence, but do not show any other cytochemical features characteristics of the mammalian APUD series. Tests with antisera to glucagon, gastrin and somatostatin all proved negative. In the oesophagus tests with all four antisera proved negative. The significance of these results is discussed in relation to the phylogeny of vertebrate gastro-intestinal hormones.

Histochemical and ultrastructural identification of neurotensin cells in the dog ileum

In the dog ileum, neurotensin cells stained with immunofluorescence or immunoperoxidase proved distinct from argentaffin (EC) cells, glucagon immunoreactive (GLI) cells and pancreatic peptide immunoreactive (PP) cells. Neurotensin cells showed various degrees of reactivity with Grimelius' silver. With electron microscopy, besides EC cells, large granule cells with a thin peripheral rim of Grimelius-reactivity (L cells) and large granule cells with variable Grimelius-reactivity of the core (N cells) were found. On distributive grounds, L cells were identified with GLI cells and N cells were interpreted as neurotensin cells.

Distribution, ontogeny and ultrastructure of the mammalian secretin cell

Immunocytochemically, secretin cells have been demonstrated to occur in the duodenum and jejunum of several mammals. Calculations on the relative frequency of such cells indicate that the bulk of secretin occurs in the jejunum, a fact supporting the view that secretin may be released by physiological stimulants other than hydrochloric acid. Electron microscopical identification of cat and pig secretin cells confirmed their identity with the ultrastructurally defined S cells, and staining experiments revealed that secretin cells were argyrophilic both with the method of Grimelius and with that of Hellerström and Hellman. Secretin cells are detected already in the 17-day old fetal rat duodenum and show a developmental pattern similar to that displayed by the gastrin cells. It is suggested that secretin may play a role in the early regulation of growth of the fetal gastrointestinal tract.

Intestinal endocrine cells of chicks around the time of hatching

The duodenum of 16-day Black Australorp chick embryos, and the duodenum, ileum, large intestine and caeca of 18-day embryos and of chicks within 30 h of hatching, have been studied by electron microscopy. Cells were found with secretory granules resembling those in mammalian EC, S, A-like, EG and D cells (terminology of Solcia et al., 1973), and were on this basis tentatively identified accordingly. The distribution and frequency of the chick cells in different parts of the tract correspond well to the situation in mammals.

Immunofluorescent localization of secretin in pancreatic monolayer culture

Immunofluorescent cells to synthetic secretin were identified in monolayer culture of neonatal rat pancreas. No cross reaction of anti-secretin was observed with either glucagon, somatostatin or gastrin. The presence of cells containing secretin or a secretin-like peptide adds a new cell type to the three already characterized (insulin, glucagon and somatostatin containing cells) in monolayer culture.

Secretin and insulin: response to intraduodenal acid

Immunoreactive secretin (IRS) and immunoreactive insulin (IRI) levels were measured in humans and dogs following the intraduodenal instillation of hydrochloric acid. IRS levels rose after acid in both instances, but a concomitant rise in peripheral IRI levels was not noted. Premedication of the humans with Scopolamine prevented a rise of IRS in the human subjects. It is concluded that the endovenous release of IRS alone does not result in increased IRI levels in peripheral blood and that IRS release may be under vagal control.

On the occurrence of argyrophil cells in salivary glands

Salivary glands (parotid, submandibular and sublingual glands) of nine mammalian species were investigated with respect to presence and localization of argyrophil and argentaffin cells. With the exception of the parotid gland of the rat, no positive staining was observed within the examined glands. In the rat parotid distinctly argyrophil cells could be demonstrated in the intercalated ducts. Histochemical studies of the cells, ultrastructural analysis of their cytoplasmic granules as well as their reactions to certain drugs indicate that these cells are of exocrine rather than of endocrine nature. After a subcutaneous injection of pilocarpine, the intensity of the argyrophil staining was markedly reduced. No specific catecholamine fluorescence could be detected within the cells, not even after pretreatment of the animals with high doses of L-DOPA. The membrane-bounded cytoplasmic granules of the intercalated duct cells furthermore displayed a strong positive staining reaction after treatment of ultrathin Vestopal sections with the periodic acid-chromic acid-silver technique of Rambourg et al. (1969).

The ultrastructure of the cell types in the endocrine pancreas of the horse

The islets of Langerhans of the equine pancreas were examined with the electron microscope after immersion or perfusion fixation. Five cell types could be distinguished after fixation by either technique: 1. A-cells, situated at the center of the islets, 2. B-cells, containing mostly "pale granules" and constituting the principal cell type of the periphery of the islets, 3. D-cells, also located mainly at the periphery of the islets, 4. G-cells, found at the edge of the islets and in the exocrine pancreas, and 5. S-cells, (small granule cells), which are relatively few in number and occur only in the islets. The function and age-dependent modifications of these cells are discussed. The formation of light and dark cells and of "mixed cells" are regarded as artifact, since cells of this type occur only under the condition of immersion fixation.

[The Verner-Morrison syndrome. The clinical picture and pathologic anatomy]

The Verner-Morrison Syndrome is a clinically defined entity caused by an islet cell tumor of the pancreas. More than 60 cases have been described so long. The syndrome is characterized by diarrhea, hypokalemia and hypochlorhydria. In addition to a diabetic disposition, raised calcium levels and skin alterations may be present. The diagnosis is a clinical one. A pancreatic tumor should be searched for and removed. Morphologically a benign and a maligne islet cell tumor or a diffuse hyperplasia of the islets of Langerhans can be found. Until now identification of the tumor cells has not been possible. There seems no doubt that the tumor cells produce a peptide hormone. Secretin, gastric inhibitory polypeptide, vasoactive intestinal polypeptide and combinations of hormones are discussed. The results are contradictory. Theories concerning the formal and causal pathogenesis are only incomplete and unproved up to now.

Gastrointestinal apudosis in obese hyperglycaemic mice

Quantitative histological and immunocytochemical studies have been carried out on the endocrine cells of the gastrointestinal tract in genetically obese mice and their heterozygous (lean) litter mates. In the ob/ob mice hyperplasia of most of the endocrine (APUD) cells of the gut was found, a condition which can be described as apudosis. Quantitative histology of silver-stained preparations, using a method which demonstrates the majority of endocrine cells, showed a significant degree of hyperplasia in all regions of the gastrointestinal tract, with statistically significant differences in the upper intestine (p = less than 0.001). Quantitative immunocytochemical studies by image analysis showed a difference in both number and hormone content of Gastric Inhibitory Peptide (GIP) (p = less than 0.001) and Enteroglucagon (EG) cells in obese as compared to lean mice. Differences in the case of Secretin (S), Gastrin (G) and Vasoactive Intestinal Peptide (VIP) cells were not great but in the obese mice both S and G cells were present in larger numbers in the lower intestine whereas in the lean, and in normal mice, they are predominant in the upper intestine. Whether these complex gut endocrine changes are primary, or secondary to the metabolic abnormalities seen in the ob/ob mouse, cannot presently be determined.

Immunochemical studies of the endocrine cells of the gastrointestinal tract. II An immunoperoxide technique for the localization of secretin containing cells in human duodenum

Endocrine cells containing secretin have been identified in the epithelium lining human duodenum by direct and indirect immunoperoxidase techniques using immune sera raised against pur natural secretin. The techniques were applied to sections of carbodiimide-fixed tissue embedded in polyethylene glycol. Some sections, stained by a modified indirect technique, were processed for electron microscopy; secretin-containing granules were present by ultrastructural preservation was too poor to be of value. The potential advantages of a peroxidase technique over fluorescein-coniugated antisera are discussed.

Ultrastructure and fluorescence histochemistry of endocrine (APUD-type) cells in tracheal mucosa of human and various animal species

This study describes distrinctive cells with ultrastructural and histochemical features of APUD-type endocrine cells within the tracheal epithelium of human fetuses, newborns and children as well as different animal species. These cells referred to as Kultschitzky cells (K cells) were found to be argyrophilic, but not argentaffin, and are considered analogous to the same type of cells in lung and gastro-intestinal tract. Fluorescence histochemistry demonstrated the presence of intracellular amine within tracheal K cells, but only after in-vitro or in-vivo administration of amine precursor (L-DOPA). Ultrastructurally, these cells are characterized by the presence of numerous cytoplasmic granules (dense core vesicles) which show species related morphologic variations. Two different types of K cells were found in trachea of lamb and armadillo, each type possessing morphologically different dense core vesicles. In human and rabbit tracheas, only one type of K cell was identified. K cells in the trachea are distributed as single cells between other epithelial cells; neuroepithelial bodies such as those found in bronchial mucosa were not identified. Well differentiated K cells were found in tracheas of early human fetuses and throughout gestation, infancy, and childhood. Preservation of K cells in human autopsy material and widespread occurence of these cells in various laboratory animals will permit further studies into the nature and function of tracheobronchial endocrine cells.

Cellular localization of a vasoactive intestinal peptide in the mammalian and avian gastrointestinal tract

Immunohistochemical studies using an antiserum to a pure porcine vasoactive intestinal peptide, possessing no cross reactivity against the related hormones glucagon, secretin, and gastrin-inhibitory peptide, revealed a wide distribution of vasoactive intestinal peptide cells throughout the entire length of the mammalian and avian gut. The highest numbers of cells were present in the small intestine and more particularly in the large intestine in all species investigated. Three types of endocrine cell in the mammalian gut are sufficiently widely distributed to be considered as the sites for production of vasoactive intestinal peptide. In the avian gut there are only two identifiable cell types. Sequential immunofluorescence and silver staining showed, in the bird, that the enterochromaffin (EC) cell was not responsible. This procedure could not be used in our mammalian gut samples but here serial section immunofluorescence for enteroglucagon and vasoactive intestinal peptide indicated that the two cells were not identical and that each was differently localized in the mucosa. These results leave the D cell of the Wiesbaden classification as the most likely site for the production of vasoactive intestinal peptide. The final identification must come from successful immune electron cytochemistry but this has not yet been achieved.

Secretin cells in coeliac disease

Immunofluorescence (anti-secretin), cytochemical, and ultrastructural studies were carried out on jejunal biopsies from 16 children with coeliac disease and from 17 controls with suspected malabsorption but normal jejunal morphology. In 11 of the 16 coeliacs there was generalized hyperplasia of endocrine cells and, specifically, of the secretin (S) cells. Further studies, on adult coeliacs as well as on children, combined with serum secretin assays, may establish whether the S cells are abnormally storing hormone because of inability to release it or because of excess production.