Characterization and tissue location of the neural adenosine receptor in the rat ileum

1 The aim of the present investigation was to characterize and determine the tissue location of the adenosine receptors present in the rat ileum using a method that detects drug action on the cholinergic nerves innervating the longitudinal and circular muscles. 2 The non-selective adenosine agonist, NECA (10 and 100 nM) caused significant concentration-related reductions in the circular muscle responses to transmural stimulation over the frequency range of 2.5-40 Hz, but did not affect the responses of the longitudinal muscle, nor did it reduce the muscle responses of the guinea-pig ileum. 3 The affinity order of antagonists at inhibiting the effect of NECA. on the circular muscle was: CPDPX > 8-PT > DMPX with apparent pA(2) values of 9.31, 7.54 and 5.63 respectively. CPDPX (10-100 nM) caused parallel displacements of the concentration-effect curves to CPA with a pK(b) value of 9.15 and Schild slope of 1.03. 4 The agonists previously tested in the rat jejunum peristaltic reflex preparation were also shown to inhibit responses of the rat ileum in the following decreasing order of potency: CPA > NECA > 2-CADO > R-PIA > S-PIA > > PAA. In addition, CHA and CCPA were also potent agonists. NECA (100 nM) and CPA (32 nM) did not inhibit carbachol (1 mu M)-induced tone of tissues pre-treated with TTX (1 mu M). 5 In conclusion, the rat ileum contains inhibitory A(1) adenosine receptors situated on cholinergic nerve endings innervating the circular muscle.