IDENTIFICATION OF PURINOCEPTORS IN THE ISOLATED STOMACH AND INTESTINEOF THE 3-SPINED STICKLEBACK GASTEROSTEUS-ACULEATUS L

1. Adenine nucleosides and nucleotides were examined for pharmacologic al activity in isolated stomach and intestine from the stickleback Gas terosteus aculeatus L. 2. Adenosine and its stable analogues all conce ntration-dependently relaxed carbachol-contracted stomach and intestin e, with no significant difference in the potency of the analogues. Onl y 8-(p-sulphophenyl) theophylline inhibited the relaxant response to a denosine in both tissues; other adenosine antagonists such as 1,3-dipr opyl-8-cyclopentylxanthine were not active. 3. ATP, alpha, beta-methyl ene ATP (alpha,beta-MeATP) and 2-methylthio ATP (2-MeSATP) all caused concentration-dependent contractions of the stomach and intestine. 4. In the stomach, the order of potency was 2-MeSATP > alpha,beta-MeATP = ATP; the P2Y-purinoceptor antagonist reactive blue 2 inhibited respon ses to ATP. 5. In the intestine, the order of potency was alpha,beta-M eATP > 2-MeSATP = ATP; reactive blue 2 did not affect responses to ATP , nor did prolonged incubation with alpha,beta-MeATP. 6. It is conclud ed that in both the stomach and intestine, adenosine is acting through a non-specific or undifferentiated P1-purinoceptor. In the stomach, h owever, the P2-purinoceptor appears to be analogous to the mammalian P 2Y-purinoceptor, and in the intestine, the receptor is more similar to the mammalian P2X-subtype, although it was not susceptible to desensi tization.