The ontogeny of purinoceptors in rat urinary bladder and duodenum

1 The ontogeny of responses to purines and analogues of smooth muscle preparations was studied in rat duodenum and rat urinary bladder. 2 Responses to adenosine and to adenosine 5′‐triphosphate (ATP) mediated by P 1 ‐ and P 2 ‐purinoceptors respectively were present as early as postnatal day 2, the earliest day studied. 3 In rat bladder, adenosine was inhibitory and ATP and adenosine 5′‐(β,γ‐methylene) triphosphonate (AMP‐PCP) were excitatory, acting on the P 2X subtype of P 2 ‐purinoceptors. Adenosine was more potent in the neonate than in the adult, while the potency of the nucleotides initially increased with age but then declined, being highest between postnatal days 10 and 25. 4 In rat duodenum also, adenosine was inhibitory, its potency being less than the adult before day 15. 5 ATP at low concentrations was inhibitory in rat duodenum at every age studied and its potency increased with age, but higher concentrations of ATP (3 μ m and above) were excitatory until day 15. Both relaxations and contractions were mediated by the P 2Y subtype of P 2 ‐purinoceptors. These ATP‐induced contractions were not inhibited by indomethacin (25 μ m ) or by tetrodotoxin (1 μ m ) and are therefore not due to prostaglandin synthesis or to ATP‐induced release of transmitter substances from nerves. 6 These results show that responses to adenosine and to adenine nucleotides are present from birth and vary with age, and that the changes seen indicate a differential development for P 1 , P 2X ‐ and P 2Y ‐purinoceptors.