Effects of exposure to sulfuric acid-aerosol on airway responsiveness in guinea pigs: concentration and time dependency.

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 (SRaw0) 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 SRawNaCl (SRaw after exposure to aerosol of 0.9% NaCl 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 +/- 0.21 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.