The effect of precursors of noradrenalin on the response to tyramine and sympathetic stimulation.

Previous observations have shown that the effects of sympathetic stimulation and of tyramine were absent in the organs of animals treated with reserpine, but that they were restored by an infusion of noradrenaline. Observations are described showing that an infusion of adrenaline did not restore the pressor action of tyramine in the cat or in the rat, but that in the rat the pressor action was restored by an infusion of dopamine, or of (-)-dopa, or of m-tyrosine,or of phenylalanine. Observations are also described showing that the effect of postganglionic stimulation of the fibres to the nictitating membrane and to the iris was restored by an infusion of dopamine or of (-)-dopa; it was restored less well by an infusion of noradrenaline. An infusion of noradrenaline did not restore the action of tyramine on the denervated iris or on the denervated vessels of the cat's foreleg. An infusion of noradrenaline appeared to increase the effect of sympathetic stimulation of the hypogastric nerves to the uterus of the virgin cat about as much as an infusion of adrenaline. An infusion of noradrenaline restored the constrictor action of nicotine on the perfused vessels of the rabbit ear.