Comparison of the sensitivity of the vaginal mucous membranes of the albino rabbit and laboratory rat to nonoxynol-9.

Studies were conducted to compare the sensitivities of the vaginal mucous membranes of the albino rabbit and albino rat to irritation by the surfactant nonoxynol-9. The purpose of this comparison was to evaluate the rat as a model for screening vaginal products for their potential irritancy. Nonoxynol-9 at various concentrations in distilled water was administered intravaginally by lavage once a day for four consecutive days. On day 5, the animals were killed and the vaginal tissues were processed and examined histopathologically. Using a predetermined semiquantitative scoring system, it was found that the intensity of irritation was concentration dependent in both species. In the rabbit, the irritation was significantly greater than that in the rat, being mild with concentrations of 2.5 and 5% and moderate to severe at 12.5 and 25%. In the rat, irritation was negligible up to 12.5%, becoming mild at 25% and more moderate at 75%. Thus the vaginal mucosa of the rabbit is more sensitive than that of the rat and may be expected to give a more exaggerated representation of the irritation potential of a compound to the human vagina than would the rat mucosa.