Abstract
In the smallest effective concentrations, histamine produced relaxation of the chick intestine. Increasing concentrations produced biphasic responses whereas high concentrations produced contraction. Relaxation responses to histamine were absent after pre-treatment with reserpine but could be acutely restored by treatment with noradrenaline or adrenaline. Relaxation responses to histamine were blocked in vitro by phentolamine, pronethalol, guanethidine, mepyramine and hexamethonium. The effect of guanethidine was partially antagonised by dexamphetamine. Histochemical evidence of adrenergic innervation of the chick gut, and of catecholamine depletion by reserpine is presented. It is concluded that, in addition to its contractile action, histamine releases catecholamine (probably adrenaline) from the chick intestine and that the mechanism of release involves a cholinergic step.
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