Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Kinesiology

Supervisor

Melling, Jamie

Abstract

The purpose of this study was to examine sex-specific differences in the blood glucose (BG) response to recurrent aerobic exercise in type 1 diabetes. Specifically, we examined the role of peak estrogen (E2) concentrations during proestrus on BG response to prolonged aerobic exercise. To do so, nineteen Sprague-Dawley rats were assigned to four exercised groups: control female (CXF; n = 5), control male (CXM; n = 5), diabetic female (DXF, n = 5) and diabetic male (DXM, n = 4). Diabetes was induced in DX groups via subcutaneous injection of low dose streptozotocin. After four days of exercise, liver glycogen and BG responses were compared. The final bout of exercise took place during proestrus when estrogen concentrations were at their highest in the female rats. No liver glycogen differences between DXF and DXM or CXF and CXM were evident. During days 1-3, DXF had lower BG concentrations during exercise, but quicker BG recovery than DXM. Therefore, fluctuating estrogen concentrations may have reduced the sex based differences in BG response and fuel selection during exercise.

Summary for Lay Audience

Type 1 diabetes mellitus (T1DM) is a disease that results in the body being unable to produce a hormone called insulin, which helps to control blood sugar levels. There is no singular cause of T1DM, and there is no known cure. Treatment of this disease includes insulin administration either by pump or injection to maintain blood sugar near normal levels. Diet and exercise can assist in the management of this disease; however, aerobic exercise, which is moderate or high intensity exercise for a prolonged period of time, can result in low blood sugar, or hypoglycemia. During aerobic exercise the body uses a combination of sugar (glucose) and fat as fuel, and for a person with T1DM it would be more beneficial to utilize primarily fat as a fuel source in order to maintain blood sugar. The female sex hormone estrogen has been shown to increase the usage of fat and spare the usage of glucose. The level of estrogen fluctuates throughout the menstrual cycle and is considerably higher during the luteal phase of the cycle, which accounts for half of the cycle length. It is possible that due to the higher estrogen levels during this phase of menstruation females with T1DM may be more likely to use fat than sugar during aerobic exercise, protecting them against exercise induced hypoglycemia to a greater degree than males with T1DM. In this thesis we studied four rodent groups: diabetic males, diabetic females, nondiabetic males and nondiabetic females. All animals underwent four consecutive days of aerobic exercise training. Vaginal cytology was used to determine the cycle length and pattern in the rats, and the female rats were staged so that the final day of exercise took place during the phase with the highest estrogen levels (proestrus). Liver samples were taken on the final day of exercise to elucidate and glycogen sparing effect. The primary findings of this study was that the diabetic females recovered from exercise faster than the diabetic males. We did not find a glycogen sparing effect between the diabetic males and the diabetic females; however, both the diabetic males and females had significantly less liver glycogen than their non-diabetic counterparts by the end of the four day protocol. These findings indicate that there is less risk of hypoglycemia to the T1DM female during recurrent aerobic exercise when estrogen levels are high, but no protective effect against liver glycogen depletion.

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