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The Distribution of Mast-Cells in the Digestive Tract ofLaboratory Animals: Its Bearings on the Problem

of the Location of Histamine in Tissues

By I. MOTA, A. G. FERRI, AND S. YONEDA(From the Laboratory for Cell Physiology, Faculty of Medicine, and Department of Histology,

Faculty of Veterinary Medicine, University of Sao Paulo, Brazil)

With two plates (figs, i and 2)

SUMMARY

The mast-cell distribution in the digestive tract of the rat, dog, cat, and guinea-pigwas studied. In the rat mast-cells were present in the tongue, oesophagus, and fore-stomach, but practically absent from the glandular stomach, duodenum, ileum, andrectum. In the other species, mast-cells were numerous throughout the whole of thedigestive tract, presenting a large individual variation. In the tongue and oesophagusmast-cells were found mainly in the submucosa and lamina propria, where they werelocated near the epithelium. In the stomach, mast-cells were more numerous in themucosa and concentrated in the muscularis mucosae and between the necks of theglands. In the duodenum, mast-cells were also more numerous in the mucosa, beingconcentrated in the muscularis mucosae and frequently also in the summit of the villi.In the ileum and rectum mast-cells were less numerous than in the stomach andduodenum, keeping the same disposition as in these. The contribution of the mast-cells to the histamine content of the digestive tract is discussed.

INTRODUCTION

MAST-CELLS are present in the digestive tract of all classes of verte-brates (Michels, 1938). Although these cells have been thoroughly

studied by Michels (1923) and by Bolton (1933) in the wall of the alimentarycanal of lower vertebrates, we could not find any report on their distributionin the digestive tract of laboratory animals. It is known that the wall of thedigestive tract has a high content of histamine, whose cellular location has notbeen ascertained. Since Riley and West (1953) have demonstrated a strikingcorrelation between the mast-cell population of a tissue and its content inhistamine, it seemed to us interesting to study the mast-cell distributionthroughout the digestive tract of some laboratory animals. In the presentpaper we report our results.

MATERIAL AND METHODS

The digestive tract, including the tongue, of ten rats, six dogs, six cats, andeight guinea-pigs, was studied. The animals were adults of both sexes. Theywere bled under ether or nembutal anaesthesia and the digestive tract imme-diately removed. The tongue was fixed by perfusion of the fixative through thevessels, and the whole tract, from oesophagus to rectum, was filled with thefixative. All the tissues were then immersed in it for 20 to 24 hours. As afixative a 1% solution of lead sub-acetate in 50% ethanol with 0-5% of aceticacid was used. This mixture has been found to be the best fixative for mast-cells[Quarterly Journal of Microscopical Science, Vol. 97, part 2, pp. 251-256, June 1956.]

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252 Mota, Ferri, and Yoneda—Mast-cells in the

(Ferri and Mota, 1955). Mast-cell distribution was studied in the tongue,oesophagus, cardiac, fundic, and pyloric regions of the stomach, duodenum,ileum, and rectum, in frozen sections 50/n thick, stained by a 1% toluidineblue solution adjusted to about pH 4 with acetic acid. Sections were mountedin Technicon mounting medium.

RESULTS

Rat. In the digestive tract of the rat mast-cells were found to be extremelynumerous in the tongue (fig. 1, A), plentiful in the oesophagus (fig. 1, B),present in small numbers in the fore-stomach (fig. 1, c), very scarce in thesubmucosa of the fundic (fig. 1, D) and pyloric regions, and practically absentfrom the duodenum (fig. 1, E), ileum, and rectum. In the tongue these cellswere found in the connective tissue between the muscle-bundles and in thelamina propria of the mucosa. In the oesophagus the mast-cells were locatedmainly in the mucosa and a few in the tunica muscularis. In the fore-stomachand in the fundic region they were found in the submucosa almost exclusively.On the other hand, the digestive tract of the rat from stomach to rectum isrich in eosinophils, which are distributed in all layers and, like the mast-cellsin other species, are located in the lamina propria of the mucosa and con-centrated in the muscularis mucosae.

Guinea-pig, dog, and cat. In these species the mast-cell distribution was veryalike and they will be described together. However, in the cat and dog mast-cells seemed to be more numerous than in the guinea-pig. Unlike the rat, inthese species, mast-cells were present in all segments of the digestive tract,but their number was quite variable, in some animals being very high, whilescarce in others. In the tongue the mast-cells had the same distribution as inthe rat, but seemed to be less numerous (fig. 1, F). Frequently these cells werefound in the connective core of the secondary papillae near the epithelium.This occurred mainly at the dorsal surface of the tongue of the guinea-pig.

In the oesophagus the mast-cells were found for the most part in the sub-mucosa and in the lamina propria and in small numbers in the muscular layer.In the lamina propria mast-cells were found near the epithelium in the con-nective tissue of the papillae (fig. 1, G), this fact being more evident here thanin the tongue. In the dog there were also many mast-cells around the acini ofthe oesophageal glands.

FIG. 1 (plate). Photomicrographs of frozen sections after fixation in lead subacetate /ethanol / acetic acid and staining in toluidine blue. Nuclei stain lightly, so that practicallyevery black dot is a mast-cell. The scales represent 20 ft.

A, tongue of rat; numerous mast-cells between the muscle-bundles.B, oesophagus of rat; note mast-cells in the submucosa.c and D, fore-stomach and glandular stomach (fundic region) of rat; few mast-cells can be

seen in the submucosa.E, duodenum of rat; no mast-cells are observed in the field.F, tongue of cat; mast-cells in the connective tissue of the papilla.G, oesophagus of guinea-pig; observe mast-cells in the lamina propria near the epithelium.H and 1, stomachs of guinea-pig and dog; note numerous mast-cells concentrated in the

mucosa, while only a few can be seen in the submucosa.

I. MOTA, A. G. FERRI, and S. YONEDA

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I. MOTA, A. G. FERRI, and S. YONEDA

Digestive Tract of Laboratory Animals 253

In the stomach, in all three regions the mast-cells were more numerous inthe mucosa than in any other layer (fig. 1, H and 1), although the mast-cellpopulation of the mucosa showed a great deal of individual variation. Mast-cells were characteristically concentrated in the muscularis mucosae (fig. 2, Aand B) or between it and the bottom of the glands, and were frequently locatedbetween the necks of the glands (fig. 2, c). Mast-cells were found very near theepithelium, and the nearer the lumen the more cells were found with only afew granules that had frequently lost their metachromasia. These cells re-called the 'atypical mast cells' of several authors (Michels, 1938, p. 306). Nodifference in the mast-cell distribution was observed between the cardiac,fundic, and pyloric region of the stomach, although they seemed to be morenumerous in the fundic region (fig. 2, D). In the submucosa as well as in themuscularis externa, there were also many mast-cells. In the latter they werelocated along the muscle-fibres.

The duodenum also was very rich in mast-cells and, in the cat and dog,sometimes much richer than the stomach. Most of the mast-cells were locatedin the mucosa and concentrated in the muscularis mucosae (fig. 2, E). Mast-cells •were also scattered through the connective core of the villi, being fre-quently located at the summit of the villi (fig. 2, F), very close to the lumen ofthe gut. Here also the mast-cells near the surface of the mucosa showed fewgranules and loss of metachromasia.

In the dog and cat, in the places where the muscularis mucosae divides intobundles that turn around the acini of the Brunner's glands, the mast-cellswere found between these glands (fig. 2, G). The mast-cells were alsofrequently found in the submucosa and in the muscularis externa.

In the ileum the mast-cells kept the same location as in the duodenum butwere less numerous. Most of these cells were located in the mucosa andscattered through the connective core of the villi (fig. 2, H). In the guinea-pigthe number of these cells was quite variable, in some animals the laminapropria of the mucosa being very rich, while in others very poor. In thelymphatic nodes or Peyer's patches of the dog and cat, mast-cells were eitherabsent or few in number.

In the rectum mast-cells were less numerous than in the duodenum andileum. They were present in the connective tissue of the lamina propria, where

FIG. 2 (plate). Photomicrographs of frozen sections after fixation in lead subacetate / ethanol /acetic acid and staining in toluidine blue. The scales represent 20/i.

A, stomach of dog (fundic region); observe the mast-cells in the muscularis mucosae which,together with the mucosa, was artificially detached from the submucosa.

B, stomach of dog (pyloric region); observe mast-cells concentrated in the muscularismucosae.

c, stomach of cat (pyloric region); mast-cells between the necks of the glands.D, stomach of guinea-pig (fundic region); mast-cells scattered in the mucosa.E, duodenum of dog; observe mast-cells concentrated in the muscularis mucosae.F, duodenum of dog; mast-cells in the summit of a villus.c, duodenum of dog; mast-cells between the Brunner's glands.H, ileum of guinea-pig; mast-cells scattered in the connective tissue of the villi.1, rectum of dog; observe mast-cells mainly in the submucosa and in the muscularis mucosae.

254 Mota, Ferri, and Yoneda—Mast-cells in the

frequently they were concentrated in the muscularis mucosae (fig. 2, 1). Theyappeared in the submucosa, mainly around its vessels and were scatteredthrough the muscle fibres in the muscularis externa.

General remarks. Some general features were common to the species ob-served with the exception of the rat. These were the large numerical variationof the mast-cells from one animal to another, the great richness of the mucosain mast-cells, the peculiar distribution of these cells concentrated in themuscularis mucosae and between it and the bottom of the glands, and theirgradual diminution from the duodenum to the rectum.

DISCUSSION

The characteristic distribution of the mast-cells throughout the digestivetract with their concentration in the mucosa seems to parallel the findings inlower vertebrates of Bolton (1933) on mast-cell distribution in the alimentarycanal of salmonoid fishes. Bolton's figures are very clear.

Recently, while this paper was being prepared, Arvy and Quivy (1955) re-ported on the mast-cell distribution in the digestive tract of the dog. Theyobtained results similar to ours.

Since recent data have suggested a relation between the mast-cells and thehistamine content of the tissues, it is interesting to compare the distribution ofthe mast-cells in the wall of the digestive tract with its histamine distribution.The wall of the digestive tract, mainly that of the stomach and duodenum,has a high content of histamine, whose cellular location and possible functionare not known (Feldberg, 1954). Histamine has been chemically isolated fromthe gastric and intestinal mucosa of several species (Bayer and Dale, 1911;Abel and Kubota, 1919; Gerard, 1922; Sacks, Ivy, Burgess, and Vandolah,

I932)-Quantitative estimates by biological assay of the histamine content of the

wall of the stomach and gut have been reported by several authors (Gavin,McHenry, and Wilson, 1933; Gaddum and Schild, 1934; Schild, 1939;Emmelin and Kahlson, 1944; Trach, Code, and Wangersteen, 1944; Douglas,Feldberg, Paton, and Schachter, 1951). These authors have shown that thehistamine content of the digestive tract is very variable from one animal toanother and that its concentration is low in the oesophagus but high in thestomach and duodenum, whence it gradually decreases to the rectum.Throughout the whole of the digestive tract, from the stomach onwards, thehistamine concentration is higher in the mucosa than in the other layers,while the submucosa contains more histamine than the muscularis externa.Particularly in the digestive tract of the dog the distribution of the histaminehas been carefully studied by Douglas and others (1951). In the stomach andsmall intestine of the dog, where the muscularis mucosae could be separatedfrom the remainder of the mucosa, most of the histamine was usually found inthe former. The cellular location of the mucosal histamine was studied byFeldberg and Harris (1953) by the Linderstrem-Lang procedure. They foundin the mucosa of the stomach two regions of higher histamine content: the

Digestive Tract of Laboratory Animals 255

region of the parietal cells and that of the muscularis mucosae. In the duo-denum they also found two levels of maximal histamine content, one near thelumen in the region of the villi, and another in the muscularis mucosae.Perhaps these authors did not observe the mast-cells because they usedformaldehyde fixation, which preserves these cells badly (Ferri and Mota,

1955)-There is a strong parallelism between the histamine and mast-cell distribu-

tion along the whole of the digestive tract, and also a great individual variation inboth. There is a relatively small quantity of both in the oesophagus and a highquantity in the stomach and duodenum, whence there is a gradual decreasein both up to the rectum. They are mainly located in the mucosa and in it theyare usually concentrated in the muscularis mucosae. In the same way, the highhistamine concentration obtained by Feldberg and Harris (1953) in the regionof the parietal cells of the gastric mucosa and near the lumen in the region of theduodenal villi could also be explained by the mast-cell concentration in theseregions. However, to this parallelism there is one exception, that of thedigestive tract of the rat, in which the high histamine content from theglandular stomach to the rectum is not paralleled by the occurrence of largenumber of mast-cells (Mota, Beraldo, Ferri, and Junqueira, 1955). Thus it ispossible that in the other species studied not all the histamine of the digestivetract is located in the mast-cells. Therefore, although the parallelism betweenhistamine and mast-cells does not prove that all the histamine of the digestivetract of the cat, dog, and guinea-pig is located in the mast-cells, it stronglysuggests that a part at least of the histamine is located in them. However,compound 48/80, which promotes a vigorous extrusion of mast-cell granules(Mota, Beraldo, and Junqueira, 1953) and has a strong depleting effect on thehistamine bound to the mast-cells of the rat (Mota, Beraldo, Ferri, and Jun-queira, 1955), has only a very small or no effect on the histamine of the diges-tive tract of the cat and guinea-pig (Smith, 1953), although their digestive tractsare rich in mast-cells. This fact may be explained by species differences,since the mast-cell of the guinea-pig is very resistant to the action of com-pound 48/80 (Mota and Vugman, unpublished data).

An interesting possibility arises from the finding of mast-cells in closeproximity to the parietal-cells in the stomach. If, as seems probable, theysecrete histamine, it could be speculated that this could serve as a stimulus tosecretion by the parietal-cell, without a detectable rise in the plasma histaminelevel.

Thanks are due to Professor J. C. U. Junqueira for his help. This workwas aided by a grant from the Conselho Nacional de Pesquizas.

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