Estradiol Attenuates Oxidative Stress, Skeletal Muscle Apoptosis, and Exercise-Induced Muscle Injury in Females

Abstract

PURPOSE: 17β-estradiol possesses anti-oxidant properties which may provide protection against the associated effects of exercise-induced muscle injury. This study's purpose was to determine if an estrogenic protective mechanism exists between genders for skeletal muscle oxidative stress, apoptosis, and muscle injury resulting from eccentric muscle contractions. METHODS: Eight males and eight females performed 7 sets of 10 eccentric repetitions at 150% 1RM of the knee extensors on the same day that corresponded to the mid-luteal (days 21–23) phase of each female's menstrual cycle. Blood and muscle biopsy samples were obtained prior to exercise and 6 and 24 h post-exercise, while additional blood samples were obtained at 48 and 72 h post-exercise. Knee extensor strength and perceived muscle soreness were determined at 6, 24, 48 and 72 h post-exercise. Blood samples were assayed for 17β-estradiol and oxidative stress markers (superoxide dismutase and 8-isoprostane) using EIA. Muscle samples were used to determine markers of mitochondrial apoptosis (bax, bcl-2, cytochrome-c) and cell death using ELISA. Myofibrillar protein and total DNA content were determined at OD595 and OD260, respectively. RESULTS: Knee extensor strength decreases were significantly greater in males than females (p <0.001) and peaked at 24 h post-exercise. Males reported greater (p <0.001) readings of muscle soreness that peaked at 24 h post-exercise. Females had greater estrogen levels throughout all time points (p < 0.001). Females had higher (p <0.001) levels of serum superoxide dismutase compared to males, while 8-isoprostane levels were higher (p 0.05). Cell death increased in males at 24h post-exercise (p0.05). Myofibrillar protein content was similar between genders but significantly decreased (p = 0.047) at 24 h post-exercise. Decreases in total DNA content were greater for males (p <0.05) and peaked at 24 h post-exercise compared to pre-exercise. CONCLUSIONS: As a result of its anti-oxidant properties and elevated levels in females, 17β-estradiol appears to reduce levels of oxidative stress, which may in fact attenuate apoptosis and muscle injury in response to a single bout of eccentric exercise otherwise observed in males.