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Carpenter RL, Lemmer JT, Francis RM, Knous JL, Sarzynski MA, Womack CJ. Tissue Plasminogen Activator And Plasminogen Activator Inhibitor-1 Gene Expression in Muscle After Maximal Acute Aerobic Exercise. JEPonline 2010;13(6):35-44. Animal studies suggest plasminogen activation in skeletal muscle is necessary for muscle repair. However, plasminogen activators have been studied little in humans. Therefore, the purposes of this study were to: 1) assess changes in skeletal muscle gene expression of fibrinolytic and coagulation factors 2) assess plasma activity of tPA and PAI-1 in response to an acute bout of maximal aerobic exercise, 3) determine if there is any relationship between muscle gene expression of tPA and PAI-1 with plasma activity levels. Six healthy, college-aged males volunteered blood and muscle samples prior to and immediately following a maximal treadmill exercise test. Muscle tissue was homogenized and purified RNA underwent RT- PCR using gene-specific primers for tPA and PAI-1 as well as biotynylation for microarray. Blood was analyzed via biofunctional immunosorbent assays for tPA and PAI-1 activity. A significant increase in tPA mRNA was seen with exercise (p=0.038) while PAI-1 mRNA showed no changes with the exercise. Muscle tPA activity showed no changes with the exercise bout. Plasma tPA showed a significant increase in activity (p<0.0001) while plasma PAI-1 activity had no change with the exercise bout. In conclusion, tPA synthesis increases in muscle following acute, high-intensity exercise and muscle production does not significantly contribute to plasma tPA increases seen with acute, high-intensity exercise. [ABSTRACT FROM AUTHOR]

In many small animals there are distinct differences in fiber-type composition among limb muscles, and these differences typically correspond to marked disparities in the oxidative capacities. However, whether there are similar differences in the oxidative capacity among leg muscles in humans is less clear. The purpose of this study was to compare the rate of phosphocreatine (PCr) recovery, a functional in vivo marker of oxidative capacity, in the lateral and medial gastrocnemius, soleus, and the anterior compartment of the leg (primarily the tibialis anterior) of humans. Subjects performed plantar flexion and dorsiflexion gated exercise protocols consisting of 70 sets of three rapid dynamic contractions (<2.86 s) at 20 s intervals (total: 23.3 min). Starting after the sixth set of contractions, 31P 2-D CSI (8 × 8 matrix, 14-16 cm FOV, 3 cm slice, TR 2.86 s) were acquired via a linear transmit/receive surface coil using a GE 3T Excite System. The CSI data were zero-filled (32 × 32) and a single FID was produced for each time point in the lateral and medial gastrocnemius, soleus, and anterior compartment. The time constant for PCr recovery was calculated from τ = -Δ t/ln[ D/( D + Q)], where Q is the percentage change in PCr due to contraction during the steady-state portion of the protocol, D the additional drop in PCr from rest, and Δ t is the interval between contractions. The τ of PCr recovery was longer ( p < 0.05) in the anterior compartment (32 ± 3 s) than in the lateral (23 ± 2 s) and medial gastrocnemius muscles (24 ± 3 s) and the soleus (22 ± 3 s) muscles. These findings suggest that the oxidative capacity is lower in the anterior compartment than in the triceps surae muscles and is consistent with the notion that fiber-type phenotypes vary among the leg muscles of humans. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In many small animals there are distinct differences in fiber-type composition among limb muscles, and these differences typically correspond to marked disparities in the oxidative capacities. However, whether there are similar differences in the oxidative capacity among leg muscles in humans is less clear. The purpose of this study was to compare the rate of phosphocreatine (PCr) recovery, a functional in vivo marker of oxidative capacity, in the lateral and medial gastrocnemius, soleus, and the anterior compartment of the leg (primarily the tibialis anterior) of humans. Subjects performed plantar flexion and dorsiflexion gated exercise protocols consisting of 70 sets of three rapid dynamic contractions (<2.86 s) at 20 s intervals (total: 23.3 min). Starting after the sixth set of contractions, (31)P 2-D CSI (8 x 8 matrix, 14-16 cm FOV, 3 cm slice, TR 2.86 s) were acquired via a linear transmit/receive surface coil using a GE 3T Excite System. The CSI data were zero-filled (32 x 32) and a single FID was produced for each time point in the lateral and medial gastrocnemius, soleus, and anterior compartment. The time constant for PCr recovery was calculated from tau = -Deltat/ln[D/(D + Q)], where Q is the percentage change in PCr due to contraction during the steady-state portion of the protocol, D the additional drop in PCr from rest, and Deltat is the interval between contractions. The tau of PCr recovery was longer (p < 0.05) in the anterior compartment (32 +/- 3 s) than in the lateral (23 +/- 2 s) and medial gastrocnemius muscles (24 +/- 3 s) and the soleus (22 +/- 3 s) muscles. These findings suggest that the oxidative capacity is lower in the anterior compartment than in the triceps surae muscles and is consistent with the notion that fiber-type phenotypes vary among the leg muscles of humans.