Effect of long-term low and moderate levels of carbon monoxide exposure on platelet counts of rabbits.

Most of the traditional studies of carbon monoxide (CO) toxicology have emphasized the dramatic effects of heavy exposure, therefore, remarkably little information is available about the consequences occurring after exposure to low concentrations similar to those found in the polluted community air. In previous studies hypoxia has been reported to cause a decrease in platelet counts in experimental animals. In an effort to investigate the abnormalities of circulating platelets in rabbits exposed to low and moderate levels of CO, three groups of animals were studied. The first (control) group of rabbits breathed ambient air whereas the second was exposed to low level CO (50 ppm by volume) for 24 hr continuously for 8 weeks. The third group was exposed to 300 ppm for 4 weeks (8 hr/day for 5 days). Per cent oxyhemoglobin (HbO2), per cent hemoglobin (Hb) and per cent carboxyhemoglobin (HbCO) and circulating platelet counts were monitored in all groups. A consistant pattern of change in circulating platelet quantity was found at the observed time intervals in CO exposed animals. No changes were observed in the same tests in rabbits exposed to ambient air. Prolonged low level CO exposure may influence change in circulating platelet counts and/or congenital platelet function disorders in man through this mechanism.