Activation of the sensory irritant receptor by C7-C11 n-alkanes.

The sensory irritation effect of vapours of n-alkanes with 7-11 carbon atoms was determined from a trigeminal reflex, decreasing the respiratory rate in mice. The maximum effect within the first 10 min of the exposure period decreased from heptane to undecane, equivalent to a decrease in intrinsic activity. The concentration which depressed the respiratory rate by 50% (RD-50) was 17,400 ppm for heptane. The n-alkanes C8-C11 were not able to produce this response level. The threshold concentration (RD-0) decreased from heptane to undecane, which corresponds to an increase in potency. The thermodynamic analysis suggests, however, that the affinity constants are equal, and thus the increase in potency is suggested to be due to altered distribution between the gas-air phase and the receptor phase. The expression 0.2. RD-0 was used to estimate the upper limits for sensory irritation which are expected to be acceptable in the industrial working environment. The corresponding limits are 1205, 605 and 125 ppm, for heptane, octane and nonane, respectively. For decane the limit is expected to be above 22 ppm. We were not able to obtain an estimate for undecane due to the low intrinsic activity. Pulmonary irritation was found to be weak, except for heptane.