[The effect of calpeptin on injury and atrophy of diaphragm under mechanical ventilation in rats].

OBJECTIVE

To investigate the effect of calpeptin on diaphragmatic injury and atrophy under controlled mechanical ventilation in rats.

METHODS

A total of 24 SPF Sprague-Dawley (SD) rats were randomly divided into anesthetized control group (CON group), 24-hour controlled mechanical ventilation group (CMV group), and 24-hour CMV + treatment with calpeptin group (CMVC group), with 8 rats in each group. Animals in the CON group received an intraperitoneal injection of pentobarbital sodium without CMV and continuous infusion of pentobarbital sodium. A small-animal ventilator was used for 24 hours in rats of CMV group. Rats of CMVC were treated with a specific calpain inhibitor calpeptin (4 mg/kg). The drug was injected subcutaneously 2 hours before and 8, 15 and 23 hours after mechanical ventilation. Changes in diaphragm ultrastructure, light microscopic picture, and myosin heavy chain (MHC) expression were observed.

RESULTS

(1) Alignment of myofilaments and normal Z-band, and the shape of mitochondria were maintained in CON group as revealed by electron microscope. The signs of misalignment of myofibrils, disruption of Z-band and vacuolar mitochondria were found in CMV group, and they were obviously improved in CMVC group. The density of muscle injury (× 10⁻²/μm²) in CMV group was significantly higher than that in control group (36.8 ± 13.7 vs. 6.4 ± 6.3, t=6.373, P=0.001), and that in CMVC group was significantly lowered (17.6 ± 9.1 vs. 36.8 ± 13.7, t=3.694, P=0.002).(2) In CON group, the diaphragm fibers appeared regular in cross section without pathologic change under light microscopy. Fuzzy muscle striations, irregular muscle fibers, centralized nuclei and swelling of capillary endothelial cells were observed in CMV group, while pathological changes in the CMVC group were milder significantly. (3) In CMV group, the density of MHCslow and MHCfast was lower compared with that of CON group, and the gray value was lowered by 61.1% (t=8.138, P=0.001) and 77.1% (t=8.844, P=0.001), respectively, especially in MHCfast. However, the gray values of MHCslow and MHCfast were increased by 1.51 folds (t=4.601, P=0.010), and 1.33 folds (t=2.859, P=0.011), respectively, after treatment with calpeptin, and the elevation was more significantly in MHCslow.

CONCLUSIONS

Diaphragmatic injury and atrophy were found after CMV for 24 hours. Calpeptin could reverse the detrimental effects of CMV, and it suggested that calpain plays an important role in modulating the ventilator-induced dysfunction of the diaphragm.