Prior heat stress induces moderation of diabetic alterations in glycogen metabolism of rats

Adaptation to one environmental stressor sometimes provides protection against additional, more intensive type of stress, a phenomenon called cross-tolerance. We aimed to estimate theprotection provided by acute heat stress (AHS) over carbohydrate disturbances in streptozotocin-diabetic rats. We investigated changes in activity of some hepatic glycolitic and gluconeogenic enzymes, and concentration of some substrates in control and diabetic animals exposed to AHS (41±0.5°C / 1 h), with 1 h and 24 h recovery at room temperature before sacrifice or induction of streptozotocin (STZ)-diabetes, respectively. AHS with 1 h-recovery before sacrifice resulted in intensive glycogenolysis, directed to endogenous glucose production and further utilization of glucose by peripheral tissues, while 24 h recovery resulted in a slight tendency towards normalization of metabolic disturbances caused by AHS. Experimental diabetes caused a significant decrease of substrates and glycolytic enzymes, but an increase of gluconeogenic enzymes. In diabetic animals previously exposed to AHS we measured a less intensive decrease of liver glycogen and glucose-6-phosphate concentration and hexokinase activity, as well as less intensive increase of liver glucose concentration, glucose-6-phosphatase and fructose-1,6-bisphosphatase activity compared to control diabetic animals that had been maintained at room temperature. Prior AHS provided some protection over diabetes-induced alterations in carbohydrate-related parameters (see graphical apstract), indicating a possible development of cross-tolerance phenomenon between the two stressors, AHS and STZ-diabetes.