EFFECTS OF CORTISONE AND TESTOSTERONE ON DIAPHRAGMATIC FUNCTION AND BIOCHEMISTRY IN THE RABBIT

The effects of cortisone and testosterone on in vivo diaphragmatic fun ction and biochemistry were assessed in rabbits to determine whether a ndrogens can prevent the effects of corticosteroids on diaphragmatic f unction and biochemistry and what mechanisms of muscle function may be altered. Cortisone altered respiratory muscle endurance and diaphragm atic glycogen and lactate levels but had little effect on diaphragmati c strength. Testosterone had no significant impact on diaphragmatic st rength, endurance, or biochemistry. However, concomitant administratio n of testosterone with cortisone blunted the effect of cortisone on re spiratory muscle endurance, even though it failed to block the effects of cortisone on diaphragmatic glycogen and lactate levels. Alteration s in respiratory muscle endurance were not due to low- or high-frequen cy contractile fatigue of the diaphragm or diaphragmatic glycogen depl etion or lactate accumulation in any of the treatment conditions. On t he other hand, alterations in central drive played a dominant role, as evidenced by alterations in inspiratory duty cycle and a falloff in t he intensity of central drive during loading. Although the exact mecha nisms underlying the alterations in central drive remain unknown, conc omitant administration of androgens with corticosteroids blunted the i mpact of corticosteroids on respiratory muscle function.