HISTOMORPHOLOGICAL PECULIARITIES OF THE PANCREATIC PARENCHYMA IN RATS WITH ALLOXAN-INDUCED DIABETES OF DIFFERENT DURATION

Abstract

Summary The study of pathohistological and morphofunctional changes in the endocrine pancreas is an integral part of experimental diabetology, which allows obtaining a significant amount of information on various aspects of the etiology and pathogenesis of diabetes and its complications using experimental animal models. Aim of the study was to conduct a comprehensive evaluation of histostructure peculiarities of the pancreas and the reparative potential of the affected pancreatic islets of Langerhans in rats with alloxan-induced experimental diabetes mellitus (EDM) of different duration. Materials and methods. The experiments were performed on 63 white non-linear adult male rats, experimental diabetes mellitus (EDМ) was induced in 53 of them (10 intact rats served as control group). At 10, 20, 25, 30, 40 and 45 days after the administration of the diabetogenic substance, the experimental animals were withdrawn from the experiment, the pancreas was removed and serial sections were made, stained with hematoxylin and eosin according to the standard technique, as well as with aldehyde fuchsin – for the identification of β-cells of the islets of Langerhans. To quantify the endocrine part of the pancreas, the average diameter of the islets of Langerhans (μm), the average number of cells in the islets of Langerhans in the profile of the histological section, as well as the specific volume of the islets of Langerhans in the pancreatic tissue (%) were studied in serial histological sections. Results. The course of alloxan-induced EDM was accompanied by significant destructive-degenerative changes in the pancreatic islets during all observation periods. On the 11th day after alloxan administration, most of the cells of the islets of Langerhans were in a state of necrosis with signs of karyopyknosis and karyorrhexis. As a result of alterative processes, the number and size of islets of Langerhans, their specific volume in the pancreatic tissue, and the average number of cells in them were greatly reduced. No specific staining of β-cells with aldehyde fuchsin was detected. Moderate swelling of the pancreatic interstitium, focal dystrophic processes in the epitheliocytes of the exocrine pancreas, sometimes with pronounced microcystic formations, were found on the 11th day of the experiment. On the 21st and 26th day after alloxan administration, the specific volume, the size of the pancreatic islets of Langerhans and their cellularity parameters continued to decrease reliably. The majority of Langerhans islets were in a state of necrosis, but signs of karyolysis, observed mainly in the center of the islets, were added to the previously existing signs of karyopyknosis and karyorrhexis. The cells of the exocrine pancreas showed no visible signs of alteration, indicating their recovery after the 11th day of the experiment. In the 31-day EDM, all the main trends observed in the previous stages of the experiment were maintained, with the exception of necrotic changes in the cells of the islets of Langerhans – no necrotic insulocytes were detected. However, no β-cells were detected in the pancreatic islets, similar to the situation on days 21 and 26 of the experiment. Similar histologic and morphometric results were obtained on day 41 of the experiment. The decrease in cytarity of the preserved islets was maximal in the 46-day EDM for the entire duration of the experiment, and aldehyde-fuchsin staining of histological sections did not reveal even single β-cells in the pancreatic islets of Langerhans. Conclusions. A single intraperitoneal administration of alloxan solution at a dose of 160 mg/kg bw to experimental animals induced pathomorphologic changes in the islet part of the pancreas, which had a significant degenerative-destructive character already on the 11th day of the experiment, increased and persisted at all its stages. The diabetogenic cytotoxin alloxan caused severe dystrophic changes in the pancreatic islets of varying intensity at all stages of the experiment – from karyopyknosis/ karyorrhexis beginning on the 11th day of observation to their burden with karyolysis beginning on the 21st day of observation. The necrobiotic processes led to a reliable decrease in the endocrine parenchyma and a decrease in the specific volume of the islets of Langerhans in the pancreatic tissue, a decrease in the average size of the islets of Langerhans with a significant reduction in their cellular composition. The beta-cells of the islets of Langerhans exceptionally served as a morphofunctional substrate for the pancreatotoxic effect of alloxan, while the cells of the exocrine pancreas did not show any significant signs of alteration already after the 11th day of the experiment. The absence of even single β-cells in the pancreatic islets at all time points of the experiment (when histological sections were stained with aldehyde-fuchsin) indicates the irreversibility of their damage and the absence of reparative regeneration. Alloxan-induced destruction of β-cells with subsequent loss of their secretory activity confirms the validity of the simulated experimental model for the development of decompensated diabetes in animals due to insulin deficiency.