Effects of cortisone and testosterone on diaphragmatic function and biochemistry in the rabbit

The effects of cortisone and testosterone on in vivo diaphragmatic function and biochemistry were assessed in rabbits to determine whether androgens can prevent the effects of corticosteroids on diaphragmatic function and biochemistry and what mechanisms of muscle function may be altered. Cortisone altered respiratory muscle endurance and diaphragmatic glycogen and lactate levels but had little effect on diaphragmatic strength. Testosterone had no significant impact on diaphragmatic strength, endurance, or biochemistry. However, concomitant administration of testosterone with cortisone blunted the effect of cortisone on respiratory muscle endurance, even though it failed to block the effects of cortisone on diaphragmatic glycogen and lactate levels. Alterations in respiratory muscle endurance were not due to low- or high-frequency contractile fatigue of the diaphragm or diaphragmatic glycogen depletion or lactate accumulation in any of the treatment conditions. On the other hand, alterations in central drive played a dominant role, as evidenced by alterations in inspiratory duty cycle and a falloff in the intensity of central drive during loading. Although the exact mechanisms underlying the alterations in central drive remain unknown, concomitant administration of androgens with corticosteroids blunted the impact of corticosteroids on respiratory muscle function.