Abstract
Structure–activity studies with a number of adenosine derivatives and analogs, measuring their relaxant effects in a variety of smooth muscle systems, were conducted in the hope of obtaining indications of the possible involvement of adenylate cyclase in their mechanism of action. While it was confirmed that a C6 aminofunction is of importance for agonist activity, several compounds, in particular the relatively potent N6-hydroxylaminopurine ribonucleoside, were not antagonized by 8-p-sulfophenyltheophylline, indicating that some nucleosides cause smooth muscle relaxation by a mechanism other than adenosine receptor stimulation. Nucleosides not bearing a C6 aminofunction were essentially inactive in rabbit intestine but showed weak relaxant effects in bovine coronary artery; this may indicate a difference between the adenosine receptor systems in these tissues and the intracellular mechanisms of relaxation. Comparing the relative potencies of compounds such as adenosine, 2-chloroadenosine, 5′-(N-ethylcarboxamido)adenosine, and (−)N6-(R-phenylisopropyl)adenosine, which have been used widely to classify adenylate cyclase-coupled adenosine receptors, no uniform pattern became apparent among different smooth muscle systems used in this study and reported in the recent literature. Thus, we conclude that a classification of smooth muscle adenosine receptors according to criteria established for cyclase-coupled receptors may be inappropriate or misleading, particularly with respect to implications of adenylate cyclase involvement in the relaxant effects of adenosine and related nucleosides.
Publisher
Canadian Science Publishing
Subject
Physiology (medical),Pharmacology,General Medicine,Physiology
Cited by
18 articles.
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