ANOXIC EFFECTS OF HIGH OXYGEN PRESSURE ON SMOOTH MUSCLE

Abstract

Exposure of isolated longitudinal duodenal muscle of the rabbit to oxygen at 75 pound pressure resulted in a progressive decrease in tonus, a decrease and irregularity in amplitude of the spontaneous rhythmic contractions and a decreased frequency of this rhythm to a point of periodic cessation interspersed by spasmodic unsustained increases in tonus. The pyloric sphincter tonus was decreased. Decompression to atmospheric pressure reversed these effects. The influence of O2 at high pressure on these isolated tissues is apparently due to a direct action on the effector cells themselves rather than to involvement of intermediate nerve endings. The similarity between the effects induced by high O2 pressure and those induced by NaCN and low O2 seems to indicate a common causal factor, which may be an increased intracellular acidity which in the case of the direct action of O2 at high barometric pressure arises from a poisoning of respiratory enzymes. In the O2 poisoning in intact animals the disturbance in the carriage of CO2 retains its importance as a causal factor. The seemingly paradoxical relationship in acute O2 poisoning, where a superabundance of O2 at high barometric pressure elicits responses typical of those induced by O2, is referred to as hyperoxic anoxia.