Purinoceptors mediating relaxation and spasm in the rat gastric fundus.
1. The relaxant and spasmogenic effects of purines and analogues were studied in longitudinal strips of rat gastric fundus to characterize the purinoceptors involved. Classification was studied by use of agonist potency orders and of antagonists in circumstances where the influence of confounding factors was reduced. In general tone was raised by carbachol (0.1 microM). 2. Adenosine produced relaxation and was potentiated by nitrobenzylthioinosine (NBTI, 0.3 and 30 microM), an adenosine-uptake inhibitor. 8-Sulphophenyl-theophylline (8-SPT, 30 microM), a selective P1-purinoceptor antagonist, antagonized adenosine and 5'-N-ethylcarboxamidoadenosine (NECA), a selective agonist at P1-purinoceptors. 3. At resting tone, adenosine 5'-triphosphate (ATP) induced a small, phasic relaxation followed by a maintained spasm. When tone was raised by carbachol, ATP induced a larger relaxation followed by a smaller spasm. NBTI did not potentiate ATP, nor did 8-SPT antagonize ATP, suggesting that ATP does not act directly or indirectly at P1-purinoceptors. 4. With raised tone, and in the presence of indomethacin (10 microM) and 8-SPT (30 microM), 2-methylthio ATP (2-MeSATP) and ATP produced relaxations followed by spasms while alpha,beta-methylene ATP (alpha,beta-MeATP) induced only relaxation; all responses were concentration-dependent. The compounds had similar slopes and maxima for relaxation and spasm. The rank orders of potency were 2-MeSATP much greater than alpha,beta-MeATP greater than ATP for relaxation and 2-MeSATP much greater than ATP for spasm.(ABSTRACT TRUNCATED AT 250 WORDS)[1]References
- Purinoceptors mediating relaxation and spasm in the rat gastric fundus. Matharu, M.S., Hollingsworth, M. Br. J. Pharmacol. (1992) [Pubmed]
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