Pertussis toxin increases isoproterenol induced relaxation in field-stimulated ileum

We investigated the effects of pertussis toxin on contraction in field-stim ulated guinea pig ileum in the absence and presence of isoproterenol. Field -stimulation elicited pertussis toxin-insensitive contractions. Cumulative addition of isoproterenol produced a maximal 52% reduction in the contracti le response. Following pertussis toxin-treatment, the maximal inhibitory ef fect of isoproterenol increased to 83%. Pertussis toxin had no effect on th e ability isoproterenol to inhibit contractions elicited by histamine agoni sts. Our results suggest that the increased effectiveness of isoproterenol in pertussis toxin-treated ileum is due to an uncoupling of the muscarinic M-2 receptor contractile mechanism. (C) 1999 Elsevier Science B.V. All righ ts reserved.