Acute bout of resistance exercise increases vitamin D receptor protein expression in rat skeletal muscle

Vitamin D and vitamin D receptor (VDR) are involved in the maintenance of skeletal muscle mass and function. Although resistance exercise is well known to enhance muscle growth and improve muscle function, the effect of resistance exercise on VDR has been unclear. We investigated intramuscular VDR expression in response to an acute bout of resistance exercise or endurance exercise. Male adult Sprague-Dawley rats were subjected to either resistance exercise (isometrically exercised via percutaneous electrical stimulation for five sets of ten 3s contractions, with a 7s interval between contractions and 3min rest intervals between sets) or endurance exercise (treadmill at 25mmin(-1) for 60min). Rats were killed immediately or 1, 3, 6 or 24h after completion of the resistance or endurance exercise, and gastrocnemius muscles were removed. Non-exercised control animals were killed in a basal state (control group). Intramuscular VDR expression was significantly higher immediately after resistance exercise and elevated for 3h after exercise compared with the control group (P<0.05), and the resistance exercise significantly increased phosphorylated ERK1/2 and Mnk1 expression (P<0.05), which may be associated with VDR expression, immediately after exercise. Additionally, intramuscular expression of cytochrome P450 27B1, an enzyme related to vitaminD metabolism, was significantly higher at 1 and 3h after exercise (P<0.05) compared with the control group. In contrast, endurance exercise had no effect on any of the measured proteins. Our results indicate that resistance exercise may be an efficient way to increase intramuscular VDR and related enzyme expression.