Effects of ambient and stagnant hypoxia on the mechanical and electrical activity of the canine upper jejunum

The effects of ambient and stagnant hypoxia on the mechanical and electrical activity of the upper jejunum were studied in 32 anesthetized dogs. A 50 or 75% reduction in oxygen content of inhaled air produced ambient hypoxia; superior mesenteric artery (SMA) occlusion or thrombin induced mesenteric thrombosis resulted in stagnant hypoxia. Induction of hypoxia was immediately followed by a transient increase in mechanical activity. A 50% reduction in oxygen content had no other effect. A 75% reduction in oxygen content resulted in a gradual decrease in electrical control activity (ECA) frequency and in the disappearance of electrical response activity (ERA), and in jejunal contractions; however, ECA persisted until cardiac arrest occurred after 30 to 45 minutes of hypoxia. Occlusion of the SMA resulted in a significant decrease in contractile activity but ECA was not affected. Thrombin induced mesenteric thrombosis produced rapid and irreversible disappearance of both electrical and mechanical activities. Jejunal contractions and ERA are dependent upon an adequate oxygenated blood supply. ECA however, is highly resistant to reduction in oxygen content of perfused blood and continues until perfusion stops.