Changes of insulin secretion and its signal transduction mechanism at early stage of severe scald in rats

Objective To observe the changes of insulin secretion in the early stage of severe scald in rats, and to explore its signal transduction mechanism. Methods Twenty-four male Wistar rats aged 7 weeks were divided into sham injury alone (SIA) group, sham injury+ BPV (HOpic) (SIB) group, scald alone (SA) group, and scald+ BPV (HOpic) (SB) group using the random number table, with 6 rats in each group. Full-thickness scald of 50% total body surface area was inflicted in rats of SA and SB groups by a 6-s immersion of the abdomen and a 12-s immersion of the back in 94 ℃ hot water. Rats in SIA and SIB groups received sham injuries through immersion of the back and abdomen in 37 ℃ warm water for 6 and 12 seconds respectively. From 0 (immediately) to 2 day (s) after injury, the rats in groups SB and SIB were intraperitoneally injected with the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway enhancer BPV (HOpic) solution (0.5 mg/mL) at the dosage of 0.6 mg/kg once a day, and the rats in groups SA and SIA were intraperitoneally injected with the same volume of dimethyl sulfoxide once a day. At post injury hour (PIH) 72, the tail blood of rats was sampled for measuring fasting blood glucose (FBG) with a glucometer, and the pancreatic tissue samples of rats was harvested for observing the pathological manifestations of islets by hematoxylin-eosin staining, counting the docked granules per 10 μm membrane of islet beta cells and calculating the proportion of insulin vesicles through the observation of the ultrastructure of islet beta cells by transmission electron microscope, and detecting the phosphorylation level of Akt in the pancreatic PI3K/Akt signaling pathway by Western blotting. Data were statistically analyzed with one-way analysis of variance and least significant difference test. Results (1) At PIH 72, the rat FBG levels in SIA and SIB groups were normal and similar (P>0.05). Compared with the levels of those two groups, the rat FBG level in SA group was increased significantly (P<0.01), while the level in SB group showed no obvious change (P>0.05). Compared with that in SA group, the rat FBG level in SB group was decreased significantly (P<0.01). (2) At PIH 72, the morphology of rat islets was complete and the islet cells distributed regularly in SIA and SIB groups. Compared with those in SIA and SIB groups, the morphology of rat islets was incomplete, the insulin vesicles in islets were common, the islet cells distributed irregularly, and the cytoplasm of some islet beta cells was lightly stained or translucent in SA group; the morphology of islets in SB group did not change obviously. Compared with those in SA group, the morphology of islets was comparatively complete, the insulin vesicles in islets were less common, the islet cells distributed comparatively regularly, and the lightly stained or translucent cytoplasm of islet beta cells was less in SB group. (3) At PIH 72, the number of docked granules per 10 μm membrane of rat islet beta cells and the proportion of insulin vesicles in SIA and SIB groups were similar (P>0.05). Compared with those in SIA and SIB groups, the number of docked granules per 10 μm membrane of rat islet beta cells in SA group was decreased significantly (P<0.01), while the proportion of insulin vesicles was increased significantly (P<0.01); the number of docked granules per 10 μm membrane of rat islet beta cells in SB group was obviously decreased (P<0.05), while the proportion of insulin vesicles did not change obviously (P>0.05). Compared with those in SA group, the number of docked granules per 10 μm membrane of rat islet beta cells in SB group was significantly increased (P<0.01), while the proportion of insulin vesicles was significantly decreased (P<0.01). (4) At PIH 72, the phosphorylation levels of Akt in SIA, SIB, SA, and SB groups were 0.91±0.03, 0.98±0.03, 0.78±0.08, and 0.87±0.08, respectively. Compared with that in SIA group, the phosphorylation level of Akt was increased obviously in SIB group (P<0.05) but was decreased significantly in SA group (P<0.01), while the level in SB group did not change obviously (P>0.05). Compared with the level in SIB group, the phosphorylation levels of Akt in SA and SB groups were decreased significantly (P<0.01). Compared with that in SA group, the phosphorylation level of Akt in SB group was increased significantly (P<0.05). Conclusions At the early stage post severe scald in rats, the activity of the pancreatic PI3K/Akt signaling pathway and the function of insulin secretion are reduced. Improving the activity of the pancreatic PI3K/Akt signaling pathway in rats can ameliorate the function of insulin secretion and recover the physiological level of blood glucose.