الفهرس 
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Abstract
Type 2 Diabetes Mellitus is an epidemic non-communicable disease that threatens health and life quality of people. Currently, there are 285 million people worldwide living with diabetes, and 90–95% have type 2 DM. This number is expected to reach 439 million by the year 2030.
A novel association with diabetes that has received a considerable attention recently is vitamin D disturbance. Some evidences indicate a high prevalence of vitamin D deficiency worldwide. Vitamin D deficiency is usually caused by low dietary vitamin D intake and reduced cutaneous production of vitamin D.
The most abundant form of vitamin D is 25-hydroxyvitamin D (25(OH)D3), which indicates the serum concentrations of vitamin D status. It exerts its biological effects through the active metabolite 1α- 25 dihydroxyvitamin D3, which serves as a ligand for vitamin D receptors (VDR). This receptor is a member of the steroid/ thyroid hormone receptor family. As many tissues express VDR, it is hypothesized that vitamin D may have a role in the pathogenesis and prevention of type 2 DM mellitus.
Aerobic exercise is the activity which increases the demand for oxygen, and causes a person´s heart to beat faster than usual. Swimming exercise is widely used in rats as a model for evaluating the effects of aerobic activity in pathological and physiological conditions. The role of regular physical training on cardiovascular and metabolic disorders, including diabetes has been assessed. However, little is known about the effect of exercise on vitamin D status in case of type 2 DM.
This work aimed to study the effect of swimming exercise on serum vitamin D level and tissue vitamin D receptors in experimentally induced type 2 DM Mellitus in rats.
The present study included 60 adult male albino-rats weighed (120-200) gm. Rats were randomly divided into 2 main groups, control (group 1) and diabetic (group 2). Each group was further subdivided equally into sedentary, and exercised.
Diabetes Mellitus was induced by single intraperitoneal (IP) dose of streptozotocin (50 mg/kg) dissolved in cold 0.01M citrate buffer (pH 4.5). After adaptation phase, exercised subgroups either diabetic or control were swimming for 60 min session, 5 times/week for 4 weeks. At the end of the experiment all rats were sacrified by decapitation and blood samples were collected and sera were separated. Extraction and homogenization of pancreas, skeletal muscle, and adipose tissue were performed for VDR assessment.
Fasting serum glucose, triglycerides, cholesterol, high Density Lipoprotein cholesterol, and free Fatty Acid (FFA) levels were evaluated. Low Density Lipoprotein and homeostasis model assessment of insulin resistance (HOMA-IR) were calculated. By ELISA techniques serum insulin, serum vitamin D levels, in addition to VDR in pancreas, muscle, and adipose tissue in each rat were assessed.
The results of the present study showed significant increase in fasting serum glucose, insulin, HOMA-IR, cholesterol, triglycerides, and low density lipoprotein levels in sedentary diabetic rats. While, high density lipoprotein, free Fatty Acid (FFA), serum level of vitamin D and pancreatic, adipose, and muscular VDR showed significant decrease in the same group. It is evident that all these parameters were reversed by swimming exercise indicating its beneficial role in type 2 DM. In sedentary and exercised diabetic rats, serum vitamin D was found to be correlated negatively with serum glucose, insulin, HOMA, cholesterol, triglycerides, and LDL and positively correlated with HDL and tissue VDR in pancreas, muscle, and adipose tissue confirming its role in modulation of metabolic consequences associated with the disease.
It could be concluded that:
• The important role of vitamin D in contributing with metabolic homeostasis and its possible role in regulation of glucose homeostasis, insulin and lipid metabolism
• Hypo-vitaminosis D and decreased tissue VDR are associated with various metabolic factors related to diabetes in sedentary type 2 diabetic rats.
• Moderate swimming exercise is beneficial in improving metabolic consequences in type2 diabetes. This could be mediated by the activated vitamin D and its receptors.
It is recommended that:
• Type 2 diabetic patients should maintain their serum vitamin D at normal levels by regular monitoring.
• An aquatic exercise program with appropriate intensity could be also suggested in those subjects.
• Future studies could be designed to investigate the effect of combination of vitamin D intake with exercise in diabetic patients.
• Future studies could be designed to investigate the effect of vitamin D on type 1 DM in patients.
• The role of vitamin D in diabetes using inflammation as the main outcome is needed to provide a more pathophysiological link.
• Investigation of more genetic polymorphism on a larger sample size to identify individuals that are more susceptible to vitamin D deficiency is also suggested.