Arterial chemoreceptor inhibition by a single inspirate containing carbon monoxide is accounted for by raised arterial PO2.

Carbon monoxide (CO) slugs (10--100 ml) injected into the inspired air of 6 hypoxic, anaesthetized cats reduced carotid body chemoreceptor discharge. The inhibition was invariably associated with a sharp rise in Pa, O2 which was continuously recorded by a fast responding intravascular electrode. This suggests that CO in solution in the blood leaving the lungs displaces O2 from blood after it was left the exchange region and that the displaced O2 raises the Pa, O2 and inhibits chemoreceptor discharge. Our results provide no support for the idea that a haemoglobin-like pigment is involved in the mechanism of arterial chemoreceptor excitation.