Dose and pH dependent effects of aspirin on Guinea-Pig ileum
Differences in environmental pH and aspirin / indomethacin dosage could explain the conflict about the role of prostaglandins in neurotransmission in guinea-pig ileum in vitro. Neither spontaneous activity nor the responses to electrical stimuli (E.S.) were affected by changing the pH of the Tyrode solution. However, the dose of aspirin (2.4 x 10-4 M) which decreases the E.S. responses in Tyrode gassed with O2(pH 8.5), does not do so if the gas phase is carbogen (pH 7.4), but the response to histamine is increased. Switching the gas phase from oxygen to carbogen in the presence of a high dose of aspirin (4 x 10-3M) causes spontaneous contractures of the ileum which are abolished by reverting to oxygen aeration. Aspirin, in addition to its role as a prostaglandin synthetase inhibitor, has direct smooth muscle effects at pH 7.4. This can explain the divergence of opinion on the role of prostaglandins in neurotransmission in guinea-pig ileum.
KeywordsAspirin Spontaneous Activity Tyrode Solution Atropine Sulphate Procaine Hydrochloride
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