Effects of exposure to sulfuric acid‐aerosol on airway responsiveness in guinea pigs: Concentration and time dependency

Abstract

We investigated the concentration and time dependency of the effects of exposure to sulfuric acid (H₂SO₄) aerosol on airway responsiveness. Two hundred and sixteen male Hartley guinea pigs were used. The animals were divided into 3 groups (n ‐72/group), with 1 group being exposed to filtered air and the other 2 to 1.0 mg/m³ or 3.2 mg/m³ H₂SO₄ aerosol. In each group, the animals were divided into 4 subgroups (n — 18/subgroup), with exposure terms of 3 d (24 h/d), 7 d, 14 d, and 30 d. Specific airway resistance (SRaw) under room air (SRaw₀) and airway responsiveness were determined 1 wk before the beginning of exposure and on the day of termination of the exposure. Specific airway resistance values under room air (SRawr₀) prior to and after exposure were compared. There was no significant change in SRaw₀ after the exposure to filtered air, 1.0 mg/m³, or 3.2 mg/m³ H2SO₄ aerosol. Our results also showed that exposure to filtered air or 1 mg/m³ H₂SO₄ aerosol did not cause any significant change in airway responsiveness to inhaled histamine aerosol, expressed as the effective concentration of histamine (EC₂₀₀His) that produced a doubling of SRaw_NaCl (SRaw after exposure to aerosol of 0.9% NaCI saline). On the contrary, exposure to 3.2 mg/m³ H₂SO₄ aerosol induced transient airway hyporesponsiveness after a 3‐d exposure [EC₂₀₀His prior to and after exposure: 1.35 ± 0.28 and 2.23 ± 0.22 mM (p < .01), respectively] and then transient hyperresponsiveness after a 14‐d exposure [EC₂₀₀His prior to and after exposure: 1.65 ± 0.27 and 0.95 ± 0.23 mM (p < .01), respectively]. Overall, the present results revealed that (1) 1.0 mg/m³ or 3.2 mg/m³ H₂SO₄ aerosol had no significant effect on SRaw₀ during a 30‐d exposure period, (2) a high concentration (3.2 mg/m³) of H₂SO₄ aerosol affected airway responsiveness during the 30‐d exposure, while a low concentration (1.0 mg/m³) of H₂SO₄ aerosol did not, and (3) the effect of exposure to 3.2 mg/m³ H₂SO₄ aerosol on airway responsiveness was transient and stimulatory or inhibitory, depending on the duration of exposure.