Development of pituitary lesions in ND4 Swiss Webster mice when estimating the sensory irritancy of airborne...

This study determined the origin of pituitary lesions found in male ND4 Swiss Webster mice following a single head-only exposure to inhaled test materials using ASTM E981-84, standard test method for estimating sensory irritancy of airborne chemicals. Necropsy and histopathology data were evaluated due to the occurrence of unexpected pituitary lesions in sham control and exposure groups. Groups of four mice were restrained in body plethysmographs and exposed for 30 min to increasing dust concentrations of one of three test chemicals to assess the ability to cause sensory irritation. Sham control and test material-exposed mice were sacrificed after a single exposure and subjected to a complete necropsy and microscopic evaluation of the pituitary gland. Control mice remained in the animal room and were not restrained in the plethysmograph. Gross observation at necropsy showed pituitary lesions in one of seven unrestrained control mice (revised to zero of seven after microscopic examination). Seven of seven sham control mice had pituitary lesions, suggesting that the lesions were not related to test material exposure. Each test material-exposed group also had pituitary lesions with high incidence (52/60 for all groups combined), which was not exposure concentration-dependent. Microscopic evaluation of the pituitary glands revealed that darkening of the gland was due to hemorrhage and confirmed that the lesions developed with 100% incidence (19/19) in plethysmograph-housed animals. The rubber neck seal used to restrict animal movement in the plethysmograph appears to have caused an increase in pressure in the blood vessels in the pituitary gland; vessels then ruptured and hemorrhaged. This finding should not adversely affect sensory irritation responses evaluated with this method.