Lack of effects of nose-only inhalation exposure on testicular toxicity inmale rats

Reductions in testicular mass, sperm motility, and mating frequency have be en attributed to the stresses caused by confinement of Sprague-Dawley male rats in nose-only inhalation exposure tubes. Testicular changes, including an increase in testicular atrophy, have been detected at an increased incid ence in male rats used in inhalation studies as compared with rats of the s ame age and strain used in oral toxicity studies. This study was designed t o determine whether nose-only exposure of male rats caused testicular toxic ity under conditions of cooling of the exposure room and appropriate acclim ation to the exposure tubes. In order to acclimate the rats to the nose-onl y inhalation exposure apparatus, all male rats were placed in the exposure tubes for at least four successively increasing time intervals (15, 30, 45, and 60 min)on 4 separate days, with a rest period of approximately 48 h be tween the first and second acclimation, Twenty male rats were exposed nose- only to filtered air for approximately 2 h per day for 28 days before cohab itation and continuing throughout a 14-day cohabitation period. To reduce t hermal stress, the exposure room temperature was maintained at 64 to 70 deg rees F, Twenty control rats were housed in the same room as the exposed rat s but were not placed in exposure tubes. End points monitored were body wei ght, testicular weight, sperm count, sperm motility, and histopathology of the testes, epididymides, prostate, and seminal vesicles. The control rats gained weight more rapidly than the exposed rats. All the rats in both grou ps mated successfully, and testicular weights, normalized to body weight, w ere similar for both groups. More importantly, there were no microscopic ch anges that could be considered an adverse effect on the reproductive tissue s in the male rats placed in exposure tubes. Thus, nose-only exposure for u p to 2 h per day for a total of 42 days did not cause adverse effects on th e reproductive organs, fertility, or reproductive performance of male rats under the conditions of this study.