Master of Science
Melling, CW James
In patients with Type I diabetes mellitus (T1DM) undergoing intensive insulin therapy, the development of insulin resistance (IR) is linked to the improper storage of intramyocellular lipid (IMCL) species. While both IR and IMCL are improved with combined aerobic and resistance training, it is unclear how these adaptations relate to individual fibre-type transitions and metabolic function. This study aimed to compare the effects of combined exercise training versus conventional and intensive insulin therapy on skeletal muscle fibres in T1DM rodents. Seventeen Sprague-Dawley rats were divided into groups: Control-Sedentary (CS; n=4), conventionally-treated T1DM sedentary (DCT; n=4), intensively-treated T1DM sedentary (DIT; n=5) and combined aerobic/resistance exercise-trained T1DM (DCE; n=4). After twelve weeks, muscle fibre type, IMCL, and muscle glycogen content were analyzed. Significant increases in IMCL storage solely in type I fibres implicate improvements in oxidative capacity rather than a shift towards more oxidative fibres as the primary mechanism for these improvements.
Summary for Lay Audience
Type 1 diabetes mellitus (T1DM) is caused by the body’s immune system targeting and destroying the Beta cells in the pancreas that are responsible for producing insulin. Therefore, most T1DM patients rely on insulin injections to maintain their blood sugar levels as close to normal as possible. The traditional (or conventional) insulin therapy consists of patients injecting insulin once or twice per day, with minimal monitoring of their blood sugar levels. The use of intensive insulin therapy has lessened the development of cardiovascular and other diabetes-related complications, though it is associated with the development of insulin resistance (IR). IR is a condition where injected insulin has a diminishing effect over time requiring progressively more insulin to achieve the same reduction in blood sugar. In the current study, IR development in T1DM is linked to the accumulation of improperly stored fat within the muscle, which is readily improved with combined endurance and resistance exercise training. In this thesis we set out further to test whether the improvements in fat storage were due to a preferential shift in the number of fibres or whether the individual fibres improved the way they stored the fat. Four groups were studied: 1) healthy but sedentary rats, 2) well-controlled intensively insulin-treated T1DM rats, 3) poorly-controlled conventionally insulin-treated T1DM rats, and 4) poorly controlled conventionally insulin-treated T1DM rats that underwent a combined exercise training program. Histochemical staining was used to determine the type of muscle fibre, and the quantity of both fat and glycogen stored in these fibres using the mixed-fibre plantaris muscle. The primary finding of the current study was that both intensive insulin therapy and combined exercise training led to a significant increase in type I fibres. However, combined exercise led to a significantly greater increase in type I fibre fat content in comparison to that of the intensive insulin-treated T1DM group. These findings would indicate that preferential shifts to type 1 fibres are evident following intensive insulin therapy and combined exercise training; however, exercise training leads to an increase in preferential fat storage to these oxidative fibres.
McBey, David P., "The Effects of Exercise Training versus Intensive Insulin Treatment on Skeletal Muscle Fibre Content in Type 1 Diabetes Mellitus Rodents" (2019). Electronic Thesis and Dissertation Repository. 6615.
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