A comparison of the anatomical structure of the pancreas in experimental animals

Abstract

As basic knowledge for evaluation of pancreatic toxicity, anatomical structures were compared among experimental animal species, including rats, dogs, monkeys, and minipigs. In terms of gross anatomy, the pancreases of dogs, monkeys, and minipigs are compact and similar to that of humans. The rat pancreas is relatively compact at the splenic segment, but the duodenal segment is dispersed within the mesentery. In terms of histology, the islet of each animal is characterized by a topographic distribution pattern of α- versus β-cells. β-cells occupy the large central part of the rat islet, and α-cells are located in the periphery and occasionally exhibit cuffing. In dog islets, β-cells are distributed in all parts and α-cells are scattered in the center or periphery of the islet (at body and left lobe); whereas β-cells occupy all parts of the islet and no α-cells are present in the islet (at right lobe). Monkey islets show two distinct patterns, that is, α-cell-rich or β-cell-rich islets, and the former represent peripheral β-cells forming an irregular ring. Minipig islets show an irregular outline, and both α- and β-cells are present in all parts of the islet, intermingling with each other. According to morphometry, the endocrine tissue accounts for <2% of the pancreas roughly in rats and minipigs, and that of monkeys accounts for >7% of the pancreas (at tail). The endocrine tissue proportion tends to increase as the position changes from right to left in the pancreas in each species.

Keywords: endocrine-exocrine interface; extra-insular endocrine cell; pancreas; peri-islet; α-cell; β-cell.

Fig. 1.

The pancreas of the rat, dog, monkey, and minipig are illustrated with positional relation to the spleen and gut. The names of the lobes (portions) are as follows: D, duodenal segment; P, parabiliary segment; G, gastric segment; S, splenic segment; R, right lobe; B, body; B_A, anterior portion of body; B_P, posterior portion of body; L, left lobe; H, head; T, tail.

Fig. 2.

Macroscopic features of the pancreas in the rat, dog, monkey, and minipig.

Fig. 3.

Histological features of the pancreas in the rat, dog, monkey, and minipig with H&E staining and immunohistochemistry for insulin and glucagon in serial sections. All photographs were taken using a 4× objective lens. Large islets are visible in the rat and monkey, and middle-sized islets are visible in the dog (left lobe) and minipig; only small islets are visible in the dog (right lobe).

Fig. 4.

Histological features of typical islets in the rat, dog, monkey, and minipig with H&E staining and immunohistochemistry for insulin, glucagon, and somatostatin in serial sections. The photographs of the rat, dog, and minipig were taken using a 20× objective lens, and those of monkey were taken using a 10× objective lens. The photographs in the second and third rows show peripheral α-cell and central α-cell islets of a dog. The photographs in the fourth row show a small islet in serial sections of the right lobe of a dog, and the inset photograph in the third column shows an extra-insular α-cell found in the same section. The photographs in the fifth and sixth rows show α-cell-rich and β-cell-rich islets of a monkey.

Fig. 5.

Percentage areas of α-, β-, and δ-cells in the pancreas of each species. The area of each endocrine cell was measured in sections immunostained for insulin, glucagon, and somatostatin. The total area of the pancreatic tissue was measured in H&E-stained sections cut sequentially. D, duodenal segment; P, parabiliary segment; G, gastric segment; S, splenic segment; R, right lobe; B, body; L, left lobe; H, head; T, tail.