Mechanisms involved in the β-cell mass increase induced by chronic sucrose feeding to normal rats

Abstract

The aim of the present study was to clarify the mechanisms by which a sucrose-rich diet (SRD) produces an increase in the pancreatic β-cell mass in the rat. Normal Wistar rats were fed for 30 weeks either an SRD (SRD rats; 63% wt/wt), or the same diet but with starch instead of sucrose in the same proportion (CD rats). We studied body weight, serum glucose and triacylglycerol levels, endocrine tissue and β-cell mass, β-cell replication rate (proliferating cell nuclear antigen; PCNA), islet neogenesis (cytokeratin immunostaining) and β-cell apoptosis (propidium iodide). Body weight (g) recorded in the SRD rats was significantly (P<0.05) larger than that of the CD group (556.0 ± 8.3 vs 470.0 ± 13.1). Both serum glucose and triacylglycerol levels (mmol/l) were also significantly higher (P<0.05) in SRD than in CD rats (serum glucose, 8.11 ± 0.14 vs 6.62 ± 0.17; triacyglycerol, 1.57 ± 0.18 vs 0.47 ± 0.04). The number of pancreatic islets per unit area increased significantly (P<0.05) in SRD rats (3.29 ± 0.1 vs 2.01 ± 0.2). A significant increment (2.6 times) in the mass of endocrine tissue was detected in SRD animals, mainly due to an increase in the β-cell mass (P=0.0025). The islet cell replication rate, measured as the percentage of PCNA-labelled β cells increased 6.8 times in SRD rats (P<0.03). The number of apoptotic cells in the endocrine pancreas decreased significantly (three times) in the SRD animals (P=0.03). The cytokeratin-positive area did not show significant differences between CD and SRD rats. The increase of β-cell mass induced by SRD was accomplished by an enhanced replication of β cells together with a decrease in the rate of β-cell apoptosis, without any evident participation of islet neogenesis. This pancreatic reaction was unable to maintain serum glucose levels of these rats at the level measured in CD animals.