A comparison of the effects of paraquat and diquat on lung compliance,lung volumes and single breath diffusing capacity in the rat

Paraquat intoxication in its initiaal stage in characterized histologically in the lungs by atelectasis, hyaline membrane formation, alveolar edema and vascular hemorrhage often into the interstitium or air spaces. Information on the functional modification of paraquat-damaged lungs has been lacking.We evaluated lung volumes, single breath diffusing capacity of the lungs for carbon monoxide (D_LCO) and static lung compliance (C_st(L))_in rats treated with paraquat or diquat. Measurements were made 12, 24, 48, and 72 h after treatment. Paraquat by intratracheal (i.t.) installation 0.5 mg/kg or by intraperitoneal injection (i.p.) 27 mg/kg significantly decreased (P<0.01) the body weight, total lung capacity (TLC), functional residual capacity (FRC), vital capacity (VC), residual volume (RV), D_LCO, apparent alveolar volume (V_A) and C_st(L). At a lower dose level (13.5 mg/kg), the effects of paraquat peaked at about 24 h following treatment, causing a significantly decreased (P<0.01) VC and TLC. Diquat i.t. or i.p. had effect on the lungs. However, diquat i.p. decreased body weight (P<0.01) and caused a slight increase (P<0.05) in VC. The data obtained are consistent with the known pathological changes seen in paraquat-damaged lungs in that, by both routes, paraquat caused severe lung damage associated with decreased elasticity of the lungs and thorax, destruction of gas exchanging alveolar surfaces, and edema. These changes were detected reliably by lung function measurements.