The effect of exercise on PAI-1 and other markers of the insulin resistance syndrome in overweight & obese individuals : the impact of work stressors and other predictors
Introduction: Obesity, and in particular central fat accumulation, is associated with a number of metabolic disturbances such as dyslipidaemia and insulin resistance. Such `clustering' of factors is known as the Insulin ResistanceS yndrome( IRS). More recently, hypofibrinolysisa s a resulto f elevated concentrations of PAI-1 at rest has been included in the IRS. Acute exercise in normal weight individuals results in an increase in fibrinolytic capacity due to a rise in t-PA and a reduction in PAI-1 concentrations. The primary aim of the following studies therefore was to determine the effect of acute exercise and exercise training on fibrinolytic markers in obese populations. The secondary aim of this work was to examine the relationships between PAI-1 concentrations and other markers of the IRS to determine a potential role for these factors in the short-term regulation of plasma PAI-1 concentrations. Methods: Premenopausal female and male overweight and obese volunteers underwent acute bouts of exercise at intensities ranging from 50% to 100% V02 max A group of obese premenopausal omen also underwent a graded maximal exerciset est to exhaustionb efore and after 12 weeks of exercise training at 50% or 70% VO2 max. Venous blood samples were taken at rest, immediately post exercise and up to 2 hours post exercise. Samples were analysed for fibrinolytic factors (t-PA, total PAI-1 & active PAI-1), markers of endothelial damage (vWF) as well as other components of the IRS including lipid profiles, insulin and leptin. Results: Plasma t-PA concentrations rose with acute exercise at intensities greater than 50% V02 max in all study populations with the exception of obese sedentary males. In all cases t-PA returned to baseline levels 30 minutes post exercise. None of the protocols administered were sufficient to lower total PAI-1 concentrations immediately post exercise but exercise at an intensity of 70% V02 max and a duration of greater than 30 minutes resulted in elevated PAI-1 concentrations 30 minutes post exercise in the overweight and obese populations. Active PAI-1 concentrations decreased with exercise either immediately or within 30 minutes post exercise at an intensity of 70% V02 max and durations greater than 30 minutes. Exercise training at both 50% and 70% V02 max increased the t-PA response to maximal exercise but only exercise training at 70% V02 max resulted in greater decrease in active PAI-1 with exercise. No factors were consistently associated with PAI-1 throughout the studies although anthropometric measures and blood pressure were regularly associated with PAI-1 at rest. Conclusions: Overall, exercise at an intensity of 70% V02 max for duration of at least 30 minutes in obese populations results in an increased fibrinolytic capacity as shown by elevated t- PA concentrations and decreased active PAI-1 concentrations. It is important to remember however that obese populations still remain hypofibrinolytic with respect to non-obese populations at rest, during exercise and in the recovery period.