Effects Of Hypoxia And Hypothermia On Glucose Tolerance And Islet Function In Rats

Objective: To observe the changes of glucose tolerance and islet function in rats under hypoxia and hypothermia,and to explore the effects of special environmental factors on glucose metabolism.Methods: 160 male SD rats were randomly divided into control group,hypoxia（low-pressure oxygen chamber,10%O₂）groups for 1,3,7,14 and 28 days,hypothermia（ambient temperature 4-8℃）groups for 1,3,7,14 and 28 days,and hypoxia + hypothermia（10%O2+4-8℃）groups for 1,3,7,14 and 28 days,with 10 rats in each group.After feeding for a certain period of time,glucose tolerance test was performed in the abdominal cavity,blood was collected from the abdominal aorta,serum was separated,and insulin,glucagon and glycated hemoglobin levels were detected by ELISA.The insulin secretion index,insulin sensitivity index and insulin resistance index were calculated and analyzed statistically.Results :1.Under pure hypoxia condition,with the prolongation of hypoxia time,the levels of fasting blood glucose and IPGTT 0.5h,1h and 2h blood glucose in rats were firstly increased and then decreased（P < 0.05）,and the highest level of blood glucose was found on the third day of hypoxia;There were no significant differences in the levels of Hb A1 c and fasting insulin among all groups（P > 0.05）,glucagon and insulin resistance index were firstly increased and then decreased（P < 0.05）,while insulin secretion index and sensitivity index were firstly decreased and then increased（P < 0.05）.2.Under the condition of hypothermia alone,with the prolongation of hypothermia,the fasting blood glucose of rats decreased first and then increased,and the blood glucose was the lowest on the first day of hypothermia,while there were no statistical differences between the IPGTT 0.5h,1h,2h blood glucose and Hb A1 c groups.With the prolongation of hypothermia,fasting insulin and insulin resistance index were firstly decreased and then increased（P < 0.05）,while glucagon and insulin sensitivity index were firstly increased and then gradually decreased（P <0.05）.3.Under the combined hypoxia and hypothermia conditions,with the prolongation of time,fasting blood glucose and IPGTT blood glucose at 0.5h,1h and2 h were firstly increased and then gradually decreased（P < 0.05）;There were no significant differences in Hb A1 c and insulin level among all groups（P > 0.05）,while glucagon and insulin resistance index increased first and then decreased（P <0.05）.The insulin secretion index and insulin sensitivity index showed a trend of decreasing first and then increasing gradually（P < 0.05）.4.Comparison of different treatment conditions at each time point showed that:（1）On day 1,3 and 7,the comparison of hypoxia,hypothermia and hypoxia+hypothermia groups showed significant increases in fasting and postprandial blood glucose,decreased insulin sensitivity and more severe insulin resistance in hypoxia group;In the hypothermia group,fasting blood glucose decreased,postprandial blood glucose remained basically unchanged,and insulin sensitivity increased.The changes of glucose metabolism and islet function in hypoxia + hypothermia group were similar to those in hypoxia group,but decreased in hypoxia +hypothermia group.（2）Comparison of hypoxia,hypothermia and hypoxia + hypothermia groups on days 14 and 28: fasting and postprandial blood glucose decreased and insulin sensitivity increased in hypoxia group;There was no significant difference in fasting and postprandial blood glucose and insulin sensitivity between the hypothermia group and the control group.The changes of glucose metabolism and islet function in hypoxia+hypothermia group were similar to those in hypoxia group,but the changes in hypoxic + hypoxic group were more obvious.Conclusion:hypoxia,hypothermia and hypoxia + hypothermia environment can affect glucose metabolism:1.Shorter periods of hypoxia（1-7 days）can lead to elevated fasting and postprandial blood glucose and decreased insulin sensitivity;Prolonged hypoxia（14-28 days）can lead to decreased fasting and postprandial blood glucose and increased insulin sensitivity.2.Hypothermia for a short period of time（1-7 days）can lead to a decrease in fasting blood glucose,basically unchanged postprandial blood glucose,decreased insulin level and increased insulin sensitivity;With the prolongation of hypothermia,the levels of fasting blood glucose,insulin and insulin sensitivity were gradually restored to the level of control group.3.The effects of hypoxia and hypothermia on fasting,postprandial blood glucose and islet function were similar to those of hypoxia: hypoxia and hypothermia were slightly weaker than hypoxia for a short period of time（1-7 days）,which was between hypoxia and hypothermia group,while hypoxia and hypothermia were more significant for a long period of time（14-28 days）.