Aortic intimal injury in rabbits. An evaluation of a threshold limit

Sixty-one rabbits were exposed to carbon monoxide, and aortae were then examined by light microscopy and transmission and scanning electron microscopy. The CO concentration in ambient air and the exposure time were varied to estimate the threshold limit for CO-induced focal intimal edema. A significantly higher incidence (P less than .0001) of focal intimal changes was present in rabbits exposed to 180 ppm of CO for four hours or more than in rabbits given a shorter or weaker exposure. The present study, as well as recent reports on the effect of low-level CO exposure on the cardiovascular system, suggests that the CO content in tobacco smoke and in heavily polluted atmospheric air may be deleterious to the arterial wall and enhance atherogenesis. A reevaluation of the recommended threshold limit for industrial CO exposure is proposed.