INTRODUCTION:

The rabbit and rat are a good experimental clinico-anatomical model in the research of number of morphological diseases in humans and animals (1-5). Rabbits are used in wide range of commercial purposes such as meat in France, Spain, Italy and some middle East countries; as hair in production of coats, regal dresses and in medical research, they are referred to as hind-gut fermenters because of the cecum (6).

The intestinal tract of mammals have two basic functions, facilitates easy absorption of nutritive materials, and act as barrier against microorganisms and different antigens includes lymphocytes, macrophage, plasma cells and paneth cells and their found to be largest endocrine gland in the body in term of both hormones and number of endocrine cells(7-9). The small intestine of rabbit is a highly complex structure, lies in the right side of abdomen, approximately 12% of the gastrointestinal volume and divided into duodenum, jejunum and ileum., that processes and digests food, largely with the help of a huge population of bacteria. The right lobe of pancreas is situated in the mesoduodenum of the duodenal loop. The luminal surface of the small intestine is covered by villi, enterocytes that cover over 90% of the cell population on the villi surface, The luminal surface of the enterocytes contains microvilli (4). The duodenum is relatively long in the rabbit. At its origin, the duodenum forms an acute angle with the pylorus, lies close to the liver, and is subject to compression by the liver. Its started at the pylorus with a cranial portion, that forming a duodenal ampulla, descending part of duodenum is fixed to the pars intermedia of the ascending colo, the ascending part is fixed to the descending colon. The bile duct opens near origin of the duodenum, pancreatic duct opens into the duodenum in about its terminus (5). The duodenum is responsible for further processing of the material from the stomach by secreting enzymes which are vital for digestion; it also mixes the digesta with these enzymes within its lumen. The primary functions of the small intestine are digestion and absorption, by mixing of the food with digestive enzymes secreted from the endocrine glands, Most of the digestion of carbohydrates and simple proteins takes place in the duodenum (10).

They are simple tubular glands in most mammals, extending from the muscularis mucosa through the thickness of the lamina propria and they open into the intestinal lumen at the villi base, in the lining epithelium of these glands are found stem cells, absorptive cells, goblet cells, paneth cells, and some enteroendocrine cells (9-11). Most studies on histology of the duodenum regard Brunner glands, these glands were discovered by John Jacob Wepter and named after the swiss anatomist Conard Brunner who first described these glands in 1687, Brunner’s glands are specific to mammals (13), they are as mucous glands and some time serous glands, their lies in submucosa of the duodenum (12-16). Brunner glands are produce an alkaline secretion that is capable to neutralizing the chymo acid of the stomach, and supporting favorable pH conditions for adequate action by pancreatic juice enzymes (17-19).

MATERIALS AND METHOD:

The study was performed using 10 of each healthy adult local breeds rabbit (Oryctolagus cuniculus) and rat (norvegius rat) during January and February 2018. They were euthanized with an overdose of ketamine administered intramuscularly. The ventral abdominal wall of each animal was removed, the intestinal tract was separated after sectioning the pylorus just before the duodenum, Each duodenal specimen was divided into three parts (cranial, descending and ascending) immediately after slaughtering was washed with normal saline solution (0.9%), ten specimens (1cm³) from different regions of each part of the duodenum were taken and fixed by 10% formalin approximately 24 hours at room temperature, and treated by routine histological processing (20). The stains were used, Harries Hematoxylin and Eosin (H&E) for the general histological components, Periodic Acid Schiff (PAS) for carbohydrates and Alcian blue pH 2.5 for carboxylated and sulphated glycoconjugate acids. The length of crypts of Lieberkuhn, counts each of crypts of Lieberkuhn, goblet cells in the crypts of Lieberkuhn and alveoli of the Brunner’s glands in tunica submucosa (X 40) in ten sections in each section used Five microscopic fields of each part of the duodenum. The mean (X-) and the standard error (S.E) were calculated for ten slides for each part of the duodenum (21).

RESULTS:

The duodenal wall of each rabbits and rats was composed of the four layers or tunicae (mucosa, submucosa, muscularis and serosa or adventitia), the duodenum of rabbits and rats not have plicae circulares and a poorly developed muscularis mucosae (Fig.1-4), mean length of crypts of Lieberkuhn in each part of the duodenum in rabbit was longer than that in rat , mean length of crypts in cranial, descending and ascending parts of rabbit duodenum were (213±13.2) μm (221.4 ±10.1) μm (224.6±17.3) μm respectively, while in cranial, descending and ascending parts of rat duodenum were (192.1±10.3) μm (200.6 ±9.4) μm (204.3±14.8) μm respectively (Table 1), mean number of crypts in cranial, descending and ascending parts of rabbit duodenum were (6±1) (9±2) (13 ±1) respectively, while in cranial, descending and ascending parts of rat duodenum were (4±1) (8±3) (11±2) respectively (Table 1). Goblet cells were unicellular mucous globular shaped between of the columnar cells in the epithelium lined each of the villi and crypts of Lieberkuhn in tunica mucosa of the duodenum each rabbit and rat (Fig. 4-6), the mean number of goblet cells was increase toward the ascending part of duodenum in each rabbit and rat, and mean their number in cranial, descending and ascending parts of rabbit duodenum were (42±5) (57±3) (87±11) respectively, while in cranial, descending and ascending parts of the rat duodenum were (37±7) (49±5) (82±5) respectively (Table 1). The goblet cells were take positive reaction with PAS and Alcian blue pH 2.5, while negative reaction with H&E in duodenum each rabbit and rat (Fig.4-6).

Brunner’s gland showed as branched coiled tubules lined by serous and mucous cells in rabbit duodenum and were composed of each the serous and mucous acini densely packed in the submucosa of duodenum, while only mucous cells in rat duodenum were only mucous acini (Fig. 2,7,8) and separated into lobules by interlobular connective tissues (Fig.2,7), their found in the submucosa of each duodenal parts in rabbit, while absent in the ascending part of rat duodenum (Table 1), the Brunner’s glands stained with PAS only in duodenum each of rabbit and rat (Fig.8). The ducts of these glands penetrate the muscularis mucosa, ascend through the lamina propria and empty into the base of intestinal glands (Fig.9), the mean number of alveoli of the Brunner glands in cranial, descending and ascending parts of the rabbit duodenum were (38±7), ( 21±1) and (12±2) respectively, while in cranial and descending parts of the rat duodenum were (26±5) (17±3) respectively (Table1).

Table (1): The mean length of crypts μm, number of each crypts, goblet cells and alveoli of the Brunner's glands (X40) per microscopic field in duodenum of rabbit and rat (Mean ± S.E)

Alveoli

Goblet cells

Crypts

Measure

Part

number

Length μm

38 ± 7

26 ± 5

42 ± 5

37 ± 7

6 ± 1

4 ± 1

213.5 ± 13.2

192.1 ± 10.3

Cranial part in rabbit

In rat

21 ± 1

17 ± 3

57 ± 3

49 ± 5

9 ± 2

8 ± 3

221.4 ± 10.1

200.6 ± 9.4

Descending part in rabbit

In rat

12 ± 2

87 ± 11

82 ± 5

13 ± 1

11 ± 2

224.6 ± 17.3

204.3 ± 14.8

Ascending part in rabbit

In rat

DISCUSSION:

The epithelial cells that line the duodenum are protected from harsh environment of acid, proteolytic enzymes, and abrasives in the lumen by a mucus layer, these mucins are secreted by goblet cells and Brunner’s glands (7). Mean number and length of crypts were increase toward the jejunum, the bases of the crypts showed considerable number of goblet cell, Goblet cells reside throughout the length of the small and large intestines and these cells increased progressively from duodenum to ileum, so the amount of mucus varies from one species to another (9). Many studies explained the dietary factors effect goblet cell numbers and modulate the secretory activity of goblet cells (7), in each rabbit and rat the mean number of the goblet cells was increase toward the last parts of the duodenum, this finding was in accordance with (2,3). The major function of goblet cells is to lubricate and protect mucosal epithelia from damage caused by food, digestive secretions, the secretion of goblet cells is alkaline mucus for neutralize of the ingesta in cooperation with Brunner's glands to protect the duodenal lumen and assist the process of digestion and absorption by maintained an appropriate liquid state of the ingesta and microorganisms, also serves as a selective barrier for absorption across the intestine (7).

In the cranial part of the duodenum in each rabbit and rat the Brunner glands are massively present than that in the other parts, and there were decreased in the quantities toward the jejunum, and absent in ascending part of rat duodenum, this is same to (22,23), The distributed of the Brunner glands several mammals starting from the gastrointestinal junction and extending to varying distances in the proximal small intestine (24-32), Herbivores have the longest distribution, omnivores a moderate distribution, and carnivores a short distribution (7). In rats the area extends one half ways down to the entry of the bile duct (23). In rabbits to extend near the jejunum (17, 25). In guinea pig only of mucous acini and the glands were well developed in the cranial part of the duodenum (30), In primates extend distally along the intestinal tract(28), in Didelphis virginia confined to a very narrow region, immediately distal to the pyloric sphincter (33), suggest the cranial part of duodenum need for greater amounts of alkaline secretion from these glands in this part for aim of neutralize of the acidic chyme come from the stomach (32). The Brunner's glands assist the function of the crypts of Lieberkuhn in transporting immunoglobulin into the duodenal lumen. In addition, the presence of lysozyme in the cells of the secretory units of Brunner's glands continuously secrete bactericidal enzyme in human (33,34), there are numerous groups of serous-type cells lying among the mucous acini in rabbit. It has long been believed that these cells are of a nature similar to those of the pancreatic acini, while they were demonstrated to be composed of only mucous cells in rat, this similar to (24), the secretory units of Brunner’s glands in the raccoon and mouse were more dilated and lined with flatter cells (34). In bison, deer, guinea pigs, vole and domestic rabbits, they contain acidic sulphated and carboxylated mucins, whereas in humans, rhesus and Japanese macaques, cats, raccoons, rats, and opossums, they contain neutral mucins. This variation not be attributed to either the order or the diet of the mammals, although rats and voles are both rodents, Brunner’s glands in the rat produce only neutral mucins, while in the vole produce acidic mucins. The existence of duodenal sub mucosal glands in the duodenum is uncontestable (7,24).

The Brunner’s glands of guinea pig were composed of only mucous acini, the secretion produced is a mixture of both acid and neutral mucins (18) The ducts of these glands penetrate the muscularis mucosae and usually pierce the base of the crypts of lieberkuhn to deliver their secretory product into the lumen of the duodenum (30), main secretory product of these glands is mucin which protects the duodenal mucosa by neutralizing acidic chyme from stomach, Mucins have been referred to as mucopolysaccharide and glycosaminoglycans (29) and possibly by the buffering capacity of its bicarbonate content, also provides optimal conditions for enzyme action on pancreatic juices (32). These secretions are respond to parasympathetic vagal stimuli (14).

Brunner's glands of the rabbit and rat when treated with alcian blue pH 2.5 stained take a negative reaction, indicating the presence of substantial amount of acid mucins, but positive with PAS staining revealed the presence of amount of mucin in the secretion of Brunner's glands. Similar to this was obtained by (24). staining properties of Brunner glands are marked differences, in bison, deer, voles and domestic rabbit they contain acidic sulphated and carboxylate mucins, whereas in humans, cats, raccoons and rats they contain neutral mucins. This variation could not be attributed to either order or the diet of the mammals (31). (30) found that in guinea pig, the deeper glands contain abundant sulfomucins with some neutral mucins. These glands contain equal amounts of neutral and sialomucins, intense staining of guinea pig Brunner's glands with PAS indicating the presence of substantial amount of neutral mucin, When AB pH 2.5 – PAS technique was employed Brunner's glands stained variably with blue and purple indicating presence of mixture of acid and neutral mucins. More intensity of blue indicates higher amount of acid mucin and moderate neutral mucin (14).

CONCLUSION:

The present study showed reversed relation between number of the crypts, goblet cells and the Brunner’s glands for neutralize of the ingesta and available the mucosal immunity to protect of the duodenal lumen against the erosive effects of the gastric juice by virtue of the mucoid nature of its secretion.

REFERENCES:

1. Davies, R. R. and Davies, J.A.E. (2003). Rabbit gastrointestinal physiology.Vet Clin Exot Anim 6:139–153.

2. Malley, O. B. (2005): Clinical Anatomy and Physiology of Exotic Species: Structure and function of mammals, birds, reptiles and amphibians. London, UK: Elsevier Saunders.Pp:163-187.

3. Kotze, S.H.; Merwe, E.L. and Ortain, M. J. (2006). The topography and gross anatomy of the gastrointestinal tract of the Cape Dune Mole-rat (Bathyergus suillus). Anatomia Histologia Embryologia. 35 (4): 259-264.

4. Brewer, N.R. (2006). Biology of the rabbit, Journal of the American Association for Laboratory Animal Science 45(1):8-24.

5. Abidu-Figueiredo, M.; Xavier-Silva, B.; Cardinot, T.; Babinski, M.and Chagas, M. (2008). Celiac artery in New Zealand rabbit: anatomical study of its origin and arrangement for experimental research and surgical practice. Pesquisa Vet. Brazil 28(5):237-240.

6. Elnagy, T.M. and Osman, I. (2010). Anatomical study of the postnatal development of the gastrointestinal tract in rabbits, Uni. of Khartoum. J. Vet. Med. and Anim. Prod. 1(2):174‐183.

7. Dellmann, H. D. and Eurell, J. A. (1998): Textbook of veterinary histology. 5th ed. Awoters Kluwer company Philadelphi, Pp: 187 -191.

8. Ahlman, H. and Nilsson, O. (2001). The gut as the largest endocrine organ in the body. Ann. Oncol., 12: 63-68.

9. Taylor, A.B. and Anderson, J. H. (1972). Scanning electron microscope observations of mammalian intestinal villi, intervilli floor and crypt tubules, Micron, 3: 43-53.

10. Coutinho, H.B.; Robalinho, T.I.; Coutinho, V.B.; Amorin, A.M.; Almeida, J.R.; Filho, J.T.; Walker, E.; King, G.; Sewell, H.F. and Wakelin, D. (1996). Immunocytochemical demonstration that human duodenal Brunner’s glands may participate in intestinal defence. J. Anat., 189 (1): 193-197.

11. Farkas, I.E. and Gero, G. (1989). The role of Brunner’s glands in the mucosal protection of the proximal part of duodenum. Acta Physiol. Hung., 73(2-3):257-260.

12. Perrin, M.R. and Curtis, B. A. (1980). Comparative morphology of the digestive system of (19) species of Southern African myomorph rodents in relation to diet and evolution. South African Journal of Zoology, 15(1):22-33.

13. Krause, W. J. (2000). Brunner’s glands: a structural, histochemical and pathological profile. Prog. Histochem. Cytochem., 35(4):259- 367.

14. Moore, B. A.; Kim, D. and Vanner, S. (2000). Neural pathways regulating Brunner’s glands secretion in guinea pig duodenum in vitro. Am. J. Physiol. Gastrointest. Liver Physiol. 279(5): 910-917.

15. Morikawa, Y.; Miyamoto, M. and Okada, T. (1993). Prenatal development of Brunner’s glands in the rat: morphometrical study. Biol. Neonate, 63(4):258-267.

16. Crescenzi, A.; Biscotti, P.; Anemona, L. and Marinozzi, V. (1988). Carbohydrate histochemistry of human Brunner`s glands. Histochemistry, 90: 47-49.

17. Emel, E.; Leven, E.; Aseman, O. and Aytul, K. (2010). Histomorphology of the Brunner gland in the Angora rabbit. Journal of Animal and Veterinary Advances, 9(5): 887-891.

18. Rashmi, A. N.and Prasad, R. (2016). Histological and histochemical observations on Brunner’s Glands of guinea pig, Journal of Dental and Medical Sciences, 15(8): 100-106.

19. Takehana, K. and Abe, M. (1986). Histochemistry of complex carbohydrates in the duodenal. Journal of the College of Dairying, 11: 371-380.

20. Luna, I. G. (1968): Manual of histology staining methods of the armed force institute of pathology.3rd ed. McGraw. Hill book company. New York. Pp: 33, 76 -168.

21. Al-Rawi, K.M.and Kalaf-Allah, I.S. (1980). Design and Analysis Agriculture Experiments. Dar-Al Kutub-Mosul, Iraq. Pp: 65, 95-107.

22. Ahmed, Y. A.; El-hafez, A. A. E. and Zayed, A. E. (2009). Hitological and histochemical studies on the esophagus, stomach and small intestine of varanus niloticus. 2(1):35-48.

23. Sababi, M.; Nilsson, E. and Holm, L. (1995). Mucus and alkali secretion in the rat duodenum: Effects of indomethacin and luminal acid. Gastroenterology, 109: 1526-1534.

24. Ainsworth, M.A.; Koss, M.A.; Hogan, D.L. and Isenberg. J.I. (1995). Higher proximal duodenal mucosal bicarbonate secretion is independent of Brunner`s glands in rats and rabbits. Gastroenterology 109 :1160- 1166.

25. Poddar, S.and Jakob, S. (1979). Mucosubstance histochemistry of Brunner’s glands, pyloric glands and duodenal goblet cells in the ferret. Histochemistry and cell biol. 65: 67–81.

26. Goyal, M. and Pandher, K. (2017). Postnatal development of Brunner glands in rabbit, Int. J. Adv. Res.5 (3): 868-876.

27. Krause, W.J. (1981). Morphological and histochemical observations on the duodenal glands of eight wild ungulate species native to North America. J Anat, 162:167–181.

28. Krause W.J. (1975). The duodenal glands of fourteen primate species, Acta anatomica, 93:580-589.

29. Treasure T (1978). The ducts of Brunner’s glands. Journal of Anatomy, 127: 299-304.

30. Mohammadpour, A. A. (2011). Morphological and histochemical study of guinea pig duodenal submucosal glands, Bulgarian Journal of Veterinary Medicine, 14(4): 201−208.

31. Schumacher, U.; Duker, M.; Katoh, M.; Jorns, J.and Krause, W.J. (2004). Histochemical similarities of mucins produced by Brunner’s glands and pyloric glands : A comparative study. J Anat Rec Part A; 278(A): 540-550.

32. Bohe, H.; Bohe, M.; Lindstrom, C. and Ohlsson, K. (1995). Pancreatic secretory trypsin inhibitor in human Brunner’s glands. J.Gastroenterol., 30(1):90-95.

33. Kirkegaard, P.; Olsen, P. S.; Nexo, E.; Holst, J. J. and Poulsen, S. S. (1984). Effect of vasoactive intestinal polypeptide and somatostatin on secretion of epidermal growth factor and bicarbonate from Brunner’s glands. Gut., 25(11):1225-1229.

34. Obuoforibo, A. A. (1975). Mucosubstances in Brunner's glands of the mouse J. Anat., 119 ( 2): 287-294.

Received on 25.10.2018 Modified on 14.11.2018

Research J. Pharm. and Tech. 2019; 12(5):2421-2424.

DOI: 10.5958/0974-360X.2019.00406.2