Recovery after anaphylaxis of isolated guinea pig ileum segments

¹ Departments of Medicine and Physiology, University of Maryland School of Medicine, Baltimore, Maryland

Following anaphylactic contraction of actively sensitized, isolated guinea pig ileum segments in a continuously aerated system, spontaneous relaxation ensues. Interruption of aeration during anaphylactic contraction consistently inhibited the relaxation phase. If aeration was resumed, relaxation promptly ensued. Such relaxation was not an all-or-none reaction, but could be made to occur in stepwise fashion by intermittent interruption of aeration. These effects of interruption of aeration on muscle tone during anaphylaxis appeared specific, since opposite tone changes were observed during contractions induced with exogenous histamine. Studies with Tyrode's solution, pretreated with 100% O₂ or with 98.5% O₂–1.5% CO₂, suggested that the mechanism of action of aeration was, in part at least, mediated by an oxygen-dependent process and implicated the active participation of intracellular histamine-inactivating systems. Although postanaphylactic ileum relaxation was also accelerated in Tyrode's solution pretreated with 100% N₂, this effect differed in important details from accelerated relaxation in oxygenated systems and appeared to depend upon impaired ability of the contractile system to respond to released histamine.