EFFECTS OF HYPOXIA ON FORCE PRODUCED BY AGONISTS AND DEPOLARIZATION AND ARISING SPONTANEOUSLY IN THE RAT UTERUS

The effects of cyanide and nitrogen on contractile activity in rat ute ri was investigated. Hypoxia significantly reduced contractile activit y produced either spontaneously, or by application of carbachol (50 mu mol l(-1)) or oxytocin (20 nmol l(-1)) in preparations from pregnant and nonpregnant rats. Hypoxia had, however, significantly smaller effe cts on agonist-evoked than on spontaneous contractions. Application of agonists under hypoxic conditions restored some degree of force to pr eparations in which spontaneous activity had been abolished. This resu lt suggests that the loss of spontaneous contractions was, in part, du e to decreased excitability of the uterus, rather than to an impairmen t of the contractile machinery. Hypoxia significantly decreased the fo rce produced by depolarization of the uterus. The effects of hypoxia o n contraction produced by agonists or depolarization were not signific antly different, suggesting that a similar mechanism may maintain forc e under these conditions, and that this mechanism does not occur durin g spontaneous activity. Lowering the external Ca2+ concentration to 0. 1 mmol l(-1) resulted in production of significantly less force in the presence or absence of agonist. The ability of hypoxia to decrease ag onist-induced force was found not to be due to the intracellular acidi fication it produces. It was concluded that uterine hypoxia may decrea se uterine contractions in vivo and a possible role in dystocia during labour was discussed.