Exercise-Induced Muscle Damage and the Potential Protective Role of Estrogen :

1. The enzyme-substrate complex of yeast cytochrome c peroxidase is used as a sensitive, specific and accurate spectrophotometric H(2)O(2) indicator. 2. The cytochrome c peroxidase assay is suitable for use with subcellular fractions from tissue homogenates as well as with pure enzyme systems to measure H(2)O(2) generation. 3. Mitochondrial substrates entering the respiratory chain on the substrate side of the antimycin A-sensitive site support the mitochondrial generation of H(2)O(2). Succinate, the most effective substrate, yields H(2)O(2) at a rate of 0.5nmol/min per mg of protein in state 4. H(2)O(2) generation is decreased in the state 4-->state 3 transition. 4. In the combined mitochondrial-peroxisomal fraction of rat liver the changes in the mitochondrial generation of H(2)O(2) modulated by substrate, ADP and antimycin A are followed by parallel changes in the saturation of the intraperoxisomal catalase intermediate. 5. Peroxisomes supplemented with uric acid generate extraperoxisomal H(2)O(2) at a rate (8.6-16.4nmol/min per mg of protein) that corresponds to 42-61% of the rate of uric acid oxidation. Addition of azide increases these H(2)O(2) rates by a factor of 1.4-1.7. 6. The concentration of cytosolic uric acid is shown to vary during the isolation of the cellular fractions. 7. Microsomal fractions produce H(2)O(2) (up to 1.7nmol/min per mg of protein) at a ratio of 0.71-0.86mol of H(2)O(2)/mol of NADP(+) during the oxidation of NADPH. H(2)O(2) is also generated (6-25%) during the microsomal oxidation of NADH (0.06-0.025mol of H(2)O(2)/mol of NAD(+)). 8. Estimation of the rates of production of H(2)O(2) under physiological conditions can be made on the basis of the rates with the isolated fractions. The tentative value of 90nmol of H(2)O(2)/min per g of liver at 22 degrees C serves as a crude approximation to evaluate the biochemical impact of H(2)O(2) on cellular metabolism.

It is well documented in both animal and human studies that unaccustomed, particularly eccentric, muscle exercise may cause damage of muscle fiber contractile and cytoskeletal components. These injuries typically include: Z-band streaming and dissolution, A-band disruption, disintegration of the intermediate filament system, and misalignment of the myofibrils. The mechanical basis for this damage is suggested to be due to the fiber strain magnitude rather than the absolute stress imposed on the fiber. We hypothesize that eccentric contraction-induced damage occurs early in the treatment period, i.e., within the first few minutes. The structural abnormalities predominate in the fast-twitch glycolytic fibers. In the final section of this paper, we hypothesize a damage scheme, based on the muscle fiber oxidative capacity as a determining factor.

A cohort of 2270 white women, aged 40-69 years at baseline, were followed for an average of 8.5 years in the Lipid Research Clinics Program Follow-up Study. There were 44 deaths due to cardiovascular disease among the 1677 nonusers of estrogens and six cardiovascular disease deaths among the 593 estrogen users. The age-adjusted relative risk (RR) of cardiovascular disease deaths in users compared with nonusers was 0.34 (95% confidence limits 0.12 to 0.81). After multivariable adjustment for potential confounding factors (age, blood pressure, and smoking), the estimated RR for estrogen use was 0.37 (95% confidence limits 0.16 to 0.88). Analyses were done to explore whether these results could be due to selection bias for estrogen use. However, the prevalence of cardiovascular disease at baseline was slightly higher in estrogen users (12%) than in nonusers (10%); furthermore, the exclusion of all women with prevalent cardiovascular disease at baseline did not alter the apparent protective effect of estrogen use on cardiovascular disease mortality (RR = 0.42, 95% confidence limits 0.13 to 1.10). Additional analyses examining the complex association between estrogen use, lipoprotein levels, and cardiovascular disease mortality suggest that the protective effect of estrogen is substantially mediated through increased high-density lipoprotein levels.