Glucose Metabolism Results & Discussion PDF

Preview

Summary

Lab Glucose Metabolism R&D...

Description

1

Glucose Metabolism Results and Discussion There is not a significant difference in AUC between the inactive, prior activity, and post-activity conditions. Results The objective of this experiment is to determine whether exercise before or after the consumption of a pure glucose solution, or remaining inactive following consumption, will affect plasma glucose concentrations, as measured by the mean AUC (which measures plasma glucose over time) in BIO 165U students. Baseline plasma glucose (before activity or ingestion of the solution) was measured using a plasma glucose monitoring system. For each of the three experimental conditions—inactive, prior activity, and post activity—plasma glucose concentration was measured in 15-minute intervals from the start of the experiment up to 60 minutes. The inactive group consumed the glucose solution at t = 0 and proceeded with the measurements. The prior activity group exercised for the first 15 minutes and then consumed the glucose solution. The post-activity group consumed the glucose solution at t = 0 and immediately began to exercise for 15 minutes. Three two-tailed, unpaired t-tests with alpha-levels of 0.05 were conducted to determine if the difference in mean AUC between any of the groups was statistically significant. This was the appropriate test because it was hypothesized that there would be a significant change in the mean AUC between the groups. The data do not show a significant difference between any of the three groups: inactive vs. prior, inactive vs. post, and prior vs. post (p = 0.21, p = 0.86, p = 0.17). The mean AUC and standard error was 571.636 ± 17.0931 for the inactive group, 544.065 ± 13.419 for the prior activity group, and 576.125 ± 18.275 for the post-activity group (figure 1). The mean plasma glucose levels for each condition, as recorded in 15-minute intervals, are visualized in figure 2. Figure 1. Each bar represents the average Area Under the Curve for each condition. There were 22 subjects in the inactivity condition, 23 in prior activity, and 24 in post-activity. The data do not show a significant difference between any of the three means.

Figure 2. This graph depicts the mean plasma glucose concentrations between subjects in each experimental condition in 15 minute intervals. They all begin with similar glucose levels; inactive and post-activity remain close, while prior activity diverges slightly.

2

Discussion This experiment demonstrated the effects of physical activity on glucose metabolism. Carbohydrates are broken down into soluble sugars, starting with salivary amylase in the mouth, and absorbed across the epithelium of the small intestine (Silverthorn, 2016). Once absorbed, the monosaccharides are transported to the peripheral tissues and cellular respiration begins. During glycolysis, glucose is broken down into pyruvate and generates a net yield of two ATPs. During pyruvate oxidation, three-carbon pyruvate undergoes oxidative decarboxylation and is converted into two-carbon acetyl-CoA, generating CO2 and two NADH molecules. The pyruvate molecules then go through the Krebs cycle and generates CO2, NADH, FADH2, and H2O. Finally, the electron transport chain utilizes the NADH and FADH2 produced from pyruvate oxidation and the Krebs cycle to generate more ATP. The body can detect an increase in plasma glucose concentration and trigger release of insulin, which stimulates glycogen synthesis in the liver and uptake of plasma glucose by adipose tissue and skeletal muscle cells. During physical activity, glucose levels are depleted, and internal processes leading to the mobilization of glucose for energy—such as glycogenolysis and gluconeogenesis—are upregulated by release of the hormone glucagon, while internal processes leading to the storage of glucose—such as glycogenesis—are downregulated. (Silverthorn, 2016). Figure 2 shows a dramatic increase in mean plasma glucose levels after ingestion of the glucose solution for each experimental condition. In all three conditions, plasma glucose levels continue to rise (as the glucose is absorbed) until the 45 minute mark, when insulin-stimulated uptake of glucose becomes observable. The prior activity condition shows a slight rise in plasma glucose concentration during low-intensity exercise (possibly due to glycogenolysis and gluconeogenesis in the liver to help provide the muscles with energy). The prior activity group has a lower mean plasma glucose concentration than the other two conditions from 0 to 45 minutes, and surpasses both of them at 60 minutes. This is likely due to mild depletion of glucose reserves during exercise, as well as the delay in activity of insulin-stimulated glucose uptake (as mentioned above). The inactivity and post-activity curves are very similar, suggesting that the mild exercise had little effect on glucose metabolism. The obtained results demonstrate that there was no significant difference in mean AUC between any two of the three groups (inactive vs. prior, inactive vs. post, and prior vs. post), meaning that there was no significant difference in mean increase of plasma glucose during the course of the experiment. It was hypothesized that exercise would lead to a significant decrease in blood glucose concentration due to depletion of glucose used to supply the body with energy. It was hypothesized that the prior activity group would have the lowest plasma glucose, due to an increase in glucose metabolism during physical exercise; followed by the post-activity group, which would begin exercise with a surplus of plasma glucose; and that the inactive group would have the highest blood glucose, as they would have a lower demand for energy. This discrepancy between expected and observed results may be attributed to differences between the internal happenings of each individual’s body, and possibly individuals not exercising vigorously enough to cause a significant depletion of glucose. It may also be attributed to the short time span of the experiment, during which the cellular processes generating the discrepancies may not have fully been carried out (Aldawi et al, 2018). One weakness of the study design was the lack of consideration of outside factors affecting blood sugar levels in subjects (other than glucose intake and current activity level), possibly leading to spurious correlations. There are many factors that influence an individual’s metabolic rate, such as their day to day activity level, sex, age, lean muscle mass amount, hormones, genetics, and diet. Basal metabolic rate is

3

difficult to obtain with complete accuracy, seeing as the true basal metabolic rate is when the rate is the lowest, and that would be when a person is sleeping. However, obtaining a MR when an individual is sleeping is extremely difficult, so the resting metabolic rate is usually obtained instead. The resting metabolic rate is often measured after an individual has fasted for twelve hours. The experiment performed only required subjects to fast for a four hour period, which could have caused slight variations in blood pressures from the subject’s actual resting metabolic rate. To alter the experiment, the subjects’ metabolic rates could be measured after a 12 hour fasting (overnight), as well as considering other variables such as sex, age and BMI of the subjects, before obtaining blood sugar readings, to better explain and determine all effects on blood sugar levels during inactivity and activity of individuals (Engelbrechtsen et al, 2018). One possible future investigation into glucose metabolism would be to perform the same (or similar) experiment in order to observe a difference in glucose metabolism between (non-diabetic) obese and lean individuals. Previous studies have shown there to be a decrease in insulin-stimulated uptake of glucose in overweight and obese individuals (Stolic et. al., 2002), and further investigation may help us to elucidate the physiological causes of insulin resistance and their implications for exercise physiology. Annotated Bibliography Aldawi N., Darwiche G., Abusnana S., Elbagir M., Elgzyri T. (2018). Initial increase in glucose variability during Ramadan fasting in non-insulin-treated patients with diabetes type 2 using continuous glucose monitoring. Libyan Med, 14 (1): 1-6. Non-insulin treated Muslim patients with type II diabetes were subjects of an observational study, where researchers monitored the patient’s blood sugar levels for pre-, early-, late-, and postRamadan fasting days. Studies showed that when compared to pre-Ramadan fasting days there was a significant increase in glucose levels at early-Ramadan fasting days, and that there were insignificant levels in late- and post-Ramadan fasting days. The data suggests that the body finds a way to equilibrate the glucose levels once the initial shock of fasting has ended and the body is able to stabilize its glucose levels and efficiently ration out its stored nutrients. Engelbrechtsen L., Mahendran Y., Jonsson A., Gjesing A., Weeke P., Jørgensen M., Færch K., Witte D., Holst J., Jørgensen T., Grarup N., Pedersen O., Vestergaard H., Torekov S., Kanters J., Hansen T. (2018). Common variants in the hERG (KCNH2) voltage-gated potassium channel are associated with altered fasting and glucose-stimulated plasma incretin and glucagon responses. BMC Genetics, 19 (15): 1-9. Homeostasis of glucose is regulated carefully by the limitation of glucose movements, where glucose is either stored or facilitated during fed- or fasted-state metabolism. The pancreatic hormone, Glucagon, in the fed-state, inhibits glycogenolysis and stimulates glycogenesis. Whereas the opposite occurs during the fasted-state metabolism. Metabolism is regulated by the ratio of insulin to glucagon. The researchers found that other variants were involved in the homeostatic control of glucose, levels of incretins, and insulin in subjects and took those other variants into consideration when conducting their experiment. Silverthorn, D.U. (2016). Digestive System: Metabolism In: Human Physiology: An Integrated Approach, 7e. Pearson Education, Inc., NY, pp. 698-725

4

Carbohydrates are absorbed primarily as glucose and is handled differently by the body when the metabolism is either in a “fed-state” or “fasted-state”. When metabolism is in a “fed-state”, glucose is used immediately for energy through the citric acid cycle and glycolysis, as well as used for synthesis of lipoprotein in the liver. Metabolism in the “fed-state” also goes through glycogenesis, where the glucose is stored in the muscles and liver as glycogen. Any excess glucose goes through lipogenesis, where it is converted into fat and stored in the adipose tissues. When the body’s metabolism is in the “fasted-state”, glucose levels increase in the kidney and liver after glycogenolysis, where glycogen polymers get broken down to glucose (or C6H13O9P for glycolysis use). Stolic, M., Russell, A., Hutley, L., Fielding, G., Hay, J., MacDonald, G., Whitehead, J., Prins, J. (2002). Glucose uptake and insulin action in human adipose tissue—influence of BMI, anatomical depot and body fat distribution. Stolic et. al. p erformed an in vitro study of basal and insulin-stimulated glucose uptake in human adipose tissue from individuals with varying BMIs and body fat distributions. In addition to comparing glucose uptake in two kinds of fat tissue, the researchers demonstrated that adipose tissue in obese patients was insulin resistant, and the distribution of insulin resistance was associated with the distribution of fat in the subject’s body....