1. Skeletal muscle fibres normally respond to insulin by absorbing glucose. Failure of skeletal muscle to respond to insulin is a major factor in the development of type II diabetes.
(a) Distinguish between type I and type II diabetes.
A study was undertaken to investigate the effect of plasma lipids on the process of glucose absorption in response to insulin by muscle fibers. Muscle was bathed in a lipid solution for 5 hours. The lipid was then washed out over the next 3 hours. The graph shows the level of plasma fatty acids and the activity of an enzyme involved in glucose absorption in response to insulin over the period of the study. (Values are means ± standard error)
(b) State the relationship between plasma fatty acid level and enzyme activity.
(c) Calculate the percentage change of enzyme activity after 5 hours exposure to lipids.
(d) Discuss, using the data, whether the effect of lipids on this enzyme is reversible.
A further study was undertaken to look at the effect of increasing the concentration of insulin on glucose absorption in muscle bathed in lipids. A wide range of insulin concentrations were used in the same type of muscle. Glucose absorption was then measured after 5 hours.
(e) Calculate the increase in glucose absorption when insulin is increased from 0 to 103 μU ml–1 for the muscle bathed in lipid.
(f) Comment on the effect of increased insulin concentration on glucose absorption in the muscle bathed in lipid.
(g) Some investigators suggest that there is a strong relationship between high lipid diet and the body’s response to insulin. Using the data provided, evaluate this hypothesis.