ISSN:
1440-1681
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
1. The effects of ATP, adenosine and N6-substituted adenosines, adenosine receptor agonists, on the twitch contraction of guinea-pig ileum evoked by transmural stimulation were evaluated.2. Adenosine and ATP produced an immediate and concentration dependent inhibition of the twitch, IC50 being 1.1 × 10−5 mol/l and 1.2 × 10−5 mol/l, respectively.3. N6-l-phenylisopropyl adenosine (L-PIA), N6-cyclohexyl adenosine (CHA) and N6-allyl adenosine also induced inhibitions which were gradual and persistent, IC50 being 2.6 × 10−8, 2.7 × 10−8 and 5.4 × 10−7 mol/l, respectively.4. Dipyridamole (10−7 mol/l), an adenosine uptake inhibitor, markedly augmented the inhibition evoked by adenosine and ATP, but not that by three N6-substituted adenosines, while theophylline (10−4mol/l) almost completely antagonized the inhibitory effects of all purine compounds. IC50 value of adenosine in the presence of dipyridamole (5 × 10−7 mol/l) was shifted to the left about 50 times from the control, whereas that of L-PIA was virtually unchanged.5. Tissue-medium ratios indicating uptake of [H]adenosine, [3H]ATP and [3H]CHA into the segment were 3.23 (s.e.m. =0.59), 3.59 (s.e.m. =0.78) and 0.41 (s.e.m. =0.04), respectively.6. These results suggest that not only adenosine and ATP but also these N6-substituted adenosines are potent agonists for the PI receptor, implying a similarity between PI and A, receptor in a functional role and these purine compounds may thereby modulate cholinergic neurotransmission by altering adenylate cyclase activity.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1440-1681.1985.tb00305.x
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