To investigate the effect of magnesium picolinate (MgPic) on lung and diaphragm of rats with acute respiratory distress syndrome (ARDS) treated with dexamethasone (Dex).

Twenty healthy adult male Sprague-Dawley rats were randomly assigned to a control group, an ARDS group, a Dex group, and a MgPic group, with five rats in each group. Rats in the control group were given 2 mL/kg isotonic NaCl solution with endotracheal atomization, and rats in the other three groups received endotracheally atomized lipopolysaccharide (4 mg/kg) to induce ARDS. After successful modeling, rats in the Dex and MgPic groups were intraperitoneally injected with Dex (1 mg·kg^-1·d^-1) for seven consecutive days. Rats in the control, ARDS, and Dex groups were fed a standard diet, while rats in the MgPic group were fed a standard diet supplemented with 500 mg/kg MgPic. After continuous feeding for seven days and fasting for 12 h, the body mass and serum Mg²⁺ concentration of rats were measured, and the lung function was evaluated, including peak inspiratory flow rate (PIF), peak expiratory flow rate (PEF), tidal volume (Vt), minute ventilation (Mv), and mid-expiratory flow rate (EF50). The wet/dry weight (W/D) ratio of lung tissue was calculated and the diaphragmatic weight was measured. The concentrations of tumor necrosis factor-alpha (TNF-α) and type Ⅲ procollagen (PCⅢ) in bronchoalveolar lavage fluid (BALF) were detected. The expression levels of transforming growth factor-beta1 (TGF-β1) in lung tissue and myosin heavy chain 2 (MYH2) in diaphragm tissue were detected by western-blotting. Quantitative real-time PCR (qRT-PCR) was used to detect the expression of TGF-β1 messenger RNA (mRNA) in lung tissue, and muscle ring finger 1 (MURF-1) and forkhead box class O1 (FoxO1) mRNA in diaphragm tissue.

The body mass, PIF, PEF, Vt, Mv, EF50, serum Mg²⁺ concentration, W/D ratio, TGF-β1 mRNA and TGF-β1 protein in lung tissue, TNF-α and PCⅢ content in BALF, diaphragmatic weight, MURF-1 mRNA, FoxO1 mRNA, and MYH2 protein in each group all showed significant differences (F = 21.248, 57.536, 34.547, 26.022, 32.458, 90.029, 79.975, 20.767, 37.857, 99.653, 64.862, 46.587, 19.187, 32.653, 41.110, 71.535; all P < 0.001). Further pairwise comparison found that compared with the MgPic group, the body mass, diaphragmatic weight, and MYH2 protein expression were significantly increased, while MURF-1 and FoxO1 mRNA expression levels were significantly decreased in the ARDS group (all P < 0.05). The body mass, diaphragmatic weight, and MYH2 protein expression were significantly decreased, while MURF-1 and FoxO1 mRNA expression levels were significantly increased in the Dex group compared with the MgPic group (all P < 0.05). The PIF, PEF, Vt, Mv, EF50, and Mg²⁺ concentration were decreased in the ARDS and Dex groups, and the levels of PIF, PEF, Vt, Mv, and EF50 were lowest in the ARDS group, while the concentration of Mg²⁺ was lowest in the Dex group compared with the MgPic group (all P < 0.05). The W/D ratio, TGF-β1 mRNA and TGF-β1 protein levels in lung tissue, and TNF-α and PCⅢ levels in BALF were obviously increased in the ARDS and Dex groups compared with the MgPic group, and the above indicators were highest in the ARDS group (all P < 0.05).

MgPic can enhance the inhibitory effect of Dex on lung tissue fibrosis, improve diaphragm atrophy caused by Dex, and help to improve lung function in rats with ARDS.