Effects of R-(+)- and S-(-)-limonene on the respiratory tract in mice

The effects of airborne R - (+) - and S - (-) - limonene were studied in co nscious BALB/c mice by continuous monitoring respiratory rate (f), tidal vo lume (V-T) and mid-expiratory flow rate (V-D) during an exposure period of 30 min. Both enantiomers decreased f from a trigeminal reflex, i.e., due to sensory irritation. The exposure concentration decreasing f by 50% ( RD50) in the first 10 min of the exposure period was estimated to be 1076 ppm fo r R - (+)-limonene and 1467 ppm for S - (-) - limonene. Results for sensory irritation of R (+) - limonene in BALB/c mice and humans are in close agre ement. The reported sensory irritation threshold is above 80 ppm in humans while the no - observed - effect level was estimated to be 100 ppm in mice. The enantiomers were devoid of pulmonary irritation or general anesthetic effects with R - (+) - limonene less than or equal to 1599 ppm and S - (-) - limonene less than or equal to 2421 ppm. R - (+) - limonene did not influ ence VT below 629 ppm. S - (-) - limonene increased V-T above 1900 ppm. Bot h enantiomers induced a mild bronchoconstrictive effect above 1000 ppm.