Effects of pH alterations and hypoxia on isolated human intestine

Effects of hypoxia and pH alterations on the spontaneous contractions and responses to cholinergic stimuli or KCl were investigated in isolated human intestines. The longitudinal strip of human intestine showed spontaneous contractions. The spontaneous contraction was abolished by hypoxia with nitrogen gas substitution (95% N2 and 5% CO2) but not by substitution with acidic (pH 6.53) or alkaline (pH 7.75) solution. Contractile responses to acetylcholine (ACh) were not altered by treatment with hypoxia or pH alterations. KCl (10 mM)-induced contraction was inhibited by hypoxia but not by pH alterations. Transmural electrical stimulation elicited a transient contraction that was blocked by tetrodotoxin or atropine. Contractions induced by electrical stimulation at a low frequency (5 Hz) was not altered by hypoxia or pH alterations. The metabolic pathway related to energy generation and utilization for the spontaneous contraction and KCl-induced contraction seems to be more dependent on oxygen supply than that for ACh-induced contraction. The contractile mechanism in human intestine seems to be resistant to pH alterations.