Effects of oestrogens on erythrocyte enzyme efflux in normal men and women

Exercise-induced muscle protein leakage in the rat. Effects of hormonal manipulation

Differences in exercise-induced muscle damage between males and females were studied in an animal model by measuring the serum activities of specific muscle enzymes (creatine kinase and aspartate aminotransferase). It was found that rats showed muscle damage, comparable to that observed in humans after long-term exercise: males were much more affected than females. For example, the CK activity in male rats immediately after exercise was 335% of the resting value, but remained unchanged in females. To test the hypothesis that oestrogens may protect the female muscle membrane, female rats were ovariectomized at different stages of sexual maturity and exercised. A clear effect of this hormonal manipulation was observed: operated animals showed post-exercise CK elevations, depending of the age at the time of ovariectomy. Rats, ovariectomized before reaching sexual maturity, showed more damage than those ovariectomized after reaching sexual maturity.

Large delayed plasma creatine kinase changes after stepping exercise

Muscle changes have been examined in 16 normal subjects (eight female) after both a 20-minute and a prolonged step test. Stepping differs from most exercise tests in that it involves eccentric contractions (negative work) in which the active muscle is lengthened. Plasma creatine kinase (CK), muscle force, contractile properties, and tenderness in the quadriceps were measured for up to 9 days after the exercise. Muscle tenderness was experienced only in the muscles that had performed eccentric contractions (i.e., stepped down). All subjects showed some early rise in CK (less than 400 IU/liter) but eight (both male and female) showed a much greater response (up to 34,500 IU/liter) which took a long time to reach peak levels (4-5 days after stepping). It is suggested that eccentric contractions involved in this form of exercise result in some particular form of muscle damage which, in susceptible subjects, may initiate changes giving rise to a large delayed release of muscle enzymes.

Studies on the variability of glutathione S-transferase from human erythrocytes

Glutathione S-transferase activity has been measured in erythrocytes from 101 subjects. Specific activity in the female subjects was significantly greater than that in the males, but there was no relationship in either sex between enzyme activity and age or between enzyme activity and the most common erythrocyte antigens. Separation of erythrocytes by age using isopycnic centrifugation showed that enzyme activity was constant during the life of the cell.

Serum creatine kinase in the detection of Duchenne muscular dystrophy carriers: effects of season and multiple testing

The usefulness of serum creatine kinase (CK) activity in the detection of Duchenne muscular dystrophy (DMD) carriers is dependent upon a reliable control distribution. In controls there is a small but reproducible seasonal variation in CK activity, with a statistically significant variation in the upper 95th percentile (78 IU/liter in May, 53 IU/liter in November, as compared with 67 IU/liter for the whole calendar year). Because CK values in DMD heterozygotes are higher in November than in May, the carrier detection rate may be highest in November. Failure to consider this seasonal variation in controls may cause misclassification of too many normal subjects. If tests are conducted throughout the year, however, the seasonal influence can be reduced by serial testing at intervals of several months. In this case, use of the highest of the results obtained in 3 tests compared with the normal range of single measurements misclassifies too many normal subjects. Use of the mean of 3 determinations provides more accurate classification.