The signal transduction pathway for A1adenosine receptor in airway smooth muscle from allergic rabbits was studied by investigating the effect of the selective A1adenosine-receptor agonist N6-cyclopentyladenosine (CPA) on tissue levels of inositol 1,4,5-trisphosphate [Ins(1,4,5) P3] measured by protein binding assay. CPA caused a rapid, transient, and concentration-dependent elevation of Ins(1,4,5) P3in airways from allergic rabbits. The agonist also produced a concentration-dependent contraction of the airway preparations from these animals. Both the Ins(1,4,5) P3and contractile responses generated by CPA were attenuated by the phospholipase C (PLC) inhibitor U-73122, indicating the coupling of these responses to PLC. The CPA-induced Ins(1,4,5) P3production observed in the allergic rabbit tissues was also inhibited by the adenosine-receptor antagonist 8-( p-sulfophenyl)-theophylline, suggesting that the effect was mediated by A1adenosine receptors. On the other hand, the A2adenosine-receptor agonist CGS-21680 was ineffective in altering the tissue concentration of Ins(1,4,5) P3, indicating that A2adenosine receptors may not be involved in the activation of PLC in the allergic rabbit airway smooth muscle. In this preparation, the Gi-Goinhibitor pertussis toxin (PTX) attenuated the CPA-induced Ins(1,4,5) P3accumulation, providing evidence that the generation of Ins(1,4,5) P3by A1adenosine-receptor stimulation is coupled to a PTX-sensitive G protein(s). The results suggest that activation of A1adenosine receptors in allergic rabbit airway smooth muscle causes the production of Ins(1,4,5) P3via a PTX-sensitive G protein-coupled PLC, and this signaling mechanism may be involved, at least in part, in the generation of contractile responses. It is hypothesized that this process may contribute to adenosine-induced bronchoconstriction in allergic asthma.