Relation in rat hind-limb blood vessels between nervous vasomotor tone and the response to vasoconstrictor drugs.

When the nervous component of the vasomotor tone of the blood vessels of the innervated rat hind limb perfused with blood was reduced by ganglion blockade, by section of the nerves to the hind limb, or by the indirect effect of drugs, the vasoconstrictor response of the blood vessels to noradrenaline was immediately increased. This increased peripheral response was observed only when the blood perfusing the hind limb was from the same animal or from a genetically similar animal. Reduction of the nervous component of the vasomotor tone also increased the constrictor response of the hind-limb blood vessels to adrenaline, ephedrine, tyramine and 5-hydroxytryptamine, but did not increase the response to angiotensin, vasopressin or S-methyl isothiourea. Pre-treatment with reserpine increased the hind-limb response to noradrenaline but reduced the response to ephedrine, tyramine and 5-hydroxytryptamine. The results suggest that, in rats, activity in the sympathetic nervous system directly influences the reactivity of peripheral blood vessels to noradrenaline and other sympathomimetic drugs.