Abstract
Abstract In the guinea-pig isolated ileum, elevation of the extracellular concentration of calcium attenuated the excitatory influence of the opiate antagonist, naloxone, upon peristalsis. Application of 4-aminopyridine, which enhances calcium influx into cells, had a still more pronounced effect. Further, 4-aminopyridine impaired the inhibitory action of both morphine and the presynaptic α-adrenergic agonist, clonidine, upon peristalsis. The present data are consistent with the view that the intestinal mechanism subjected to naloxone blockade may function similarly to that proposed to explain the action of narcotics or of presynaptic α-adrenergic agonists upon other preparations. This mode of action may involve a reduction in the quantity of intracellular free ionized calcium available to the stimulus-release-coupling mechanism.
Published Version
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