Evaluation of concentration-response relationships for histamine and sulfuric acid aerosols in unanesthetized guinea pigs for their effects on ventilatory response to CO2.

Through the addition of aerosols to 10% CO2 mixtures, acute respiratory responses can be detected in unanesthetized guinea pigs. This conclusion was supported by results from a previous study conducted in our laboratory in which animals were exposed to nebulized histamine or sulfuric acid while placed in a whole-body plethysmograph. In that study, only one concentration of each agent was examined. The present data were collected over a wider range of histamine and sulfuric acid exposure concentrations and the results served to reinforce the previous conclusion regarding the ease in detecting acute responses with this approach. Again, inspiratory volume (VI) and pressure changes (delta P), proportional to inspired volume, were measured continously and significant decreases in these parameters occurred during aerosol challenges. In addition, respiratory frequency (f) was evaluated during all exposures but few changes in frequency were observed other than the increases induced by 10% CO2 alone. Measurements of VI and delta P indicated similar levels of response to the tested aerosols, except during intense bronchoconstriction evoked by higher concentrations of histamine. In such constricted states, VI was a more sensitive indicator. Concentration-response relationships for histamine and sulfuric acid using VI measurements were comparable to those of other investigators who measured airflow resistance. Therefore, the new method offers many advantages over previous methods through its noninvasive and simple features yet there is comparable sensitivity to detect acute responses, as demonstrated by this study.