Comparative immunohistochemistry studies on pancreas of domestic animals

Introduction

The pancreas is an example for mixed gland and consists of exo and endocrine portions. It is a soft, encapsulated, lobulated gland. The function of exocrine portion is secretion of digestive enzymes and ions into the gastrointestinal tract i.e duodenum, which are necessary for digestion of food, whereas, the lightly stained endocrine part secretes hormones i.e glucagon, insulin and somatostatin by α, β and δ cells of islets of Langerhans and they are highly vascularised and key regulators of glucose homeostatis. The endocrine part of pancreas consisted of cellular aggregations interspersed irregularly between the acini i.e islets of Langerhans and they were organized into round or polygonal clumps of cells in between the exocrine part. The acini contained a small lumen and were lined by pyramidal cells with basal, spherical nucleus. In pancreas, the exocrine component was far larger in domestic animals (Nickel et al. 1979) [20] , Dellmann and Eurell, (1998) [4] and Konig and Leibich (2004) [15] . Gautam (2015) [7] noted that the 98% of pancreas consists of exocrine part, while only 2% of the tissue makes the endocrine portion in pancreas of humans. But literature is scanty in pancreas of domestic animals. Therefore present study was undertaken to see comparative immunohistochemistry on pancreas of domestic animals.

Results

In the present study, three types of immunoreactive cells i.e glucagon (A or α cells), insulin (B or β cells) and somatostatin (D or δ cells) were observed in the islets of Langerhans in the pancreas of buffalo sheep, goat, dog and pig. The immunoreactive cells were also noticed in parenchyma of exocrine portion of pancreas and epithelium of the inter and intralobular duct in some animals. The glucagon immunoreactive cells were present at the periphery of the islets of Langerhans in buffalo (Fig. 1 & Table .2), sheep (Fig. ) when compared to other types of islet cells and most of the insulin immunoreactive cells were scattered throughout the islet especially center of the islet in buffalo (Fig. 6), dog and pig while, these insulin IR cells were distributed widely in most part of the islet of Langerhans in sheep (Fig. 7). These IR cells showed strong immunoreactivity for insulin than the other islet cells in pig (Fig. 8 & Table .5) and dog (Fig. 9 & Table .6). Moderate number of insulin immunoreactive cells were also noted between the epithelial cells of the inter and intralobular ducts in buffalo (Fig. 10 & Table .2) but absent in dog and pig. Some insulin IR cells were also observed between the exocrine portion as small islets or individual cells in buffalo, sheep and goat. The somatostatin immunoreactive cells were observed at the periphery of theislet of Langerhans in pancreas of buffalo (Fig. 11 & Table .2), sheep (Fig. 12 & Table .3), pig (Fig. 13 & Table .5), dog (Fig. ). These cells were scattered randomly between glucagon and insulin IR cells. They were distributed as isolated or individual cells between exocrine portion, but their presence was not observed in inter and intralobular ducts in buffalo, sheep, dog and pig while observed in goat.

Discussion

Immunohistochemical studies on endocrine part of pancreas of buffaloes, sheep, goat, dog and pig was studied. In the present study, the glucagon immunoreactive (IR) cells were placed at the periphery of islets of Langerhans in buffaloes, sheep, goat and pig. Similar findings were also reported by Hawkins et al. (1987) [11] in dog pancreas, Hiratsuka et al.

(1996) [13] in cows, Timurkaan et al. (2006) [23] and Budipitojo et al. (2016) [2] in pigs, Gustavsen et al. (2008) [9] in goats, Prakash et al. (2014) [21] in Madras red sheep, Hafez et al. (2015) [10] in bovines and camel, Tsuchitani et al. (2016) [24] in dogs, monkeys and minipigs. Contrary to the above findings, Karaca et al. (2014) [14] in cat, Helmstaedter et al. (1976) [12] , Furoka et al. (1989) [5] and Hafez et al. (2015) [10] in horses reported glucagon IR cells in the centre of the islet of Langerhans.

Further, in the present study, some alpha cells were scattered as small groups or isolated cells in the exocrine portion of pancreas in buffaloes, sheep, goat and pig. But in dogs the cells were also observed in between the lining epithelium of interlobular ducts. These findings were supported by Helmstaedter et al. (1976) [12] and Hafez et al.

(2015) [10] in horses and Lucini et al. (1988) [17] in bovines, Ku and Lee (2005) [16] in mice. Contrary to the above findings Timurkaan et al. (2006) [23] and Budipitojo et al.

(2016) [2] noted more number of alpha cells in the exocrine portion of pancreas of porcupine. In the present study, the small clusters of alpha cells were also noted within the connective tissue adjacent to the pancreatic duct in dog.

The percentage of α IR cells in large islets was 14.13% in buffalo, 20.86% in sheep, 16.88% in goat, 24.12 in dog% and 18.83% pigs, whereas, in medium islets their percentage was 14.98% in buffalo, 14.51% in sheep, 9.90% in goat, 13.69% in dog and 12.33% in pig. Hiratsuka et al. (1996) [13] noted 15 to 17% of α cells in cows, which is almost similar to the present findings in buffalo. But 20.40% of alpha cells were reported by Ku and Lee (2005) [16] in nude mice and 30% of α cells in humans pancreatic islets (Da and Xavier, 2018) [3] .

The insulin IR cells (β cells) were more in number in islets of pancreas compared to other types of cells. Most of these cells were located centrally and few cells were scattered at the periphery of the islets in buffaloes. Similar findings were also reported by Nakajima et al. (1988) [19] in bovines, Hiratsuka et al. (1996) [13] in cows and Hafez et al. (2015) [10] in bovines. Further, some insulin IR cells were also observed between the exocrine portion as small islets or individual cells. The above results were in conformity with the findings of Forssmann et al. (1977) [12] , Gersell et al.

(1979) [8] , Hawkins et al. (1987) [11] in dogs, Reddy and Elliott (1985a) [22] in goat foetus, Mahesh et al. (2017) [18] in goats, Prakash et al. (2014) [21] in sheep Helmstadter et al.

(1976) [12] , Furoka et al. (1989) [5] and Hafez et al. (2015) [10] in horses and Timurkaan et al. (2006) [23] and Budipitijo et al. (2016) [2] in pigs.

In the present study, the presence of β IR cells in large islets were 69.51% in buffalo, 65.36% in sheep, 71.81% in goat, 60.72% in dogs and 70.97% in pigs, whereas the medium islets consisted of 67.72% in buffalo, 67.92% in sheep, 67.62% in goat, 73.01% in dog and 73.04% in pig. Hiratsuka et al. (1996) [13] reported 72.8% beta cells in cow. Whereas, Da and Xavier (2018) [3] reported 60% of β cells in humans islets. In humans, β-cells were comparatively less in number when compared to domestic animals.

In the pancreas of buffalo, sheep, goat, dog and pig the somatostatin immunoreactive cells were very few in number and their number was least among the islet cells and observed at the periphery of the islet of Langerhans.

Helmstaedter et al. (1976) [12] and Furuoka et al. (1989) [5] also noted somatostatin cells between glucagon and insulin cell groups and Hawkins et al. (1987) [11] reported delta cells randomly and less in number in pancreas of dogs similar to the present findings in domestic animals.

The somatostatin IR cells were present between glucagon and insulin IR cells peripherally in medium and large-sized islet of Langerhans. They were distributed as isolated or individual cells between exocrine portion, but their presence was not observed in inter and intralobular ducts. Further, in the pancreas of sheep and goat few somatostatin IR cells were also noted in the center of the islet. The few somatostatin IR cells showed cytoplasmic processes in the islets. Similarly, Prakash et al. (2014) [21] also noted the delta cells peripherally in the islets of Langerhans with cytoplasmic process in Madras red sheep. Whereas, Hafez et al. (2015) [10] reported the clumps of few numbers of δ cells throughout the islets in camel and a few δ cells in peripheral location in the bovine pancreas as noted in the present study. Further, Budipitojo et al. (2016) [2] observed somatostatin cells in mantle area and a few numbers in central and peripheral areas and also few cells were noticed between acinar cells of exocrine of pancreas in porcine.

In the present study, the δ IR cells in large islets were 11.25% in buffalo, 9.61% in sheep, 8.14% in goat, 10.19% in dogs and 6.57% in pigs whereas, medium islets consisted of 10.83% in buffalo, 11.59% in sheep, 14.89% in goat, 8.62% in dog and 10.28% in pig. Ku and Lee (2005) [16] also noted somatostatin immunoreactive cells on peripheral parts of islets similar to glucagon secreting alpha cells with 2.10±1.66 and 15.60±2.95/100 cell frequencies in the central and peripheral regions and in the splenic lobe respectively. Similarly, in the duodenal lobe noticed 0.69±0.70 and 8.90±7.65/100 frequencies of cells in the central and peripheral regions respectively in mice. Timurkaan et al.

(2006) [23] noted that the somatostatin cells were mainly present in the mantle zones and at a lesser extent in the peripheral regions. Few were also scattered in the central regions of the pancreatic islets and in the exocrine portions in porcupine as observed in the present study.

In buffalo, sheep, goat, dog and pig the α cells were distributed peripherally and insulin secreting β cells in the center of the islets. According to Tsuchitani et al. (2016) [24] the β cells were occupied the large central part of the rat islet, α cells and few δ cells were located peripherally as observed in the present study. In monkey, few δ cells were located in the periphery and occasionally at the center of islet, whereas in minipig islets showed an irregular outline and α and β cells and few δ cells were scattered in all parts of the islet. 1), sheep (Fig. 2), pig (Fig . 3), goat (Fig . 4) and dog (Fig. 5) ABC method x 400 6), sheep (Fig. 7), pig (Fig . 8) and dog (Fig. 9). ABC method x 400 11), sheep (Fig. 12), pig (Fig . 13), dog (Fig. 14) and goat (Fig . 15). ABC method x 400

Conclusion

This study provides a comprehensive overview of the distribution and frequency of glucagon, insulin, and somatostatin IR cells in the pancreas of domestic animals, highlighting species-specific differences and similarities. These findings contribute to our understanding of the morphology and function of the endocrine pancreas in these species.

References

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