OBSERVATIONS ON THE RETURN OF VASCULAR TONE AFTER SYMPATHECTOMY

Abstract

Vasoconstriction, induced by struggle and other means, was studied in the normal and denervated ears of rabbits and of totally sympathectomized cats, both by direct observation and by temp. records taken with thermocouples. The diam. of denervated vessels (rabbit), unlike those normally innervated, was not affected by moderate changes of body temp. Struggle caused constriction of denervated vessels in both rabbits and sympathectomized cats, similar in its time course to that produced by intravenous adrenaline. Other drugs (acetyl-choline, pitressin, histamine) did not mimic the effect of struggle. The denervated vessels became gradually more sensitive to vasoconstrictors during the first few days after operation. Removal of the adrenal glands and of the celiae and mesenteric ganglia did not prevent the typical constriction of denervated vessels during struggle. In 2 of the 12 sympathectomized cats the typical response was absent. Adrenaline and sympathin were considered the agents producing this vasoconstriction, when it was present. The importance of using sympathectomized animals promptly to avoid confusing regeneration is stressed. No evidence was obtained for the existence of "myogenic" or "intrinsic" vascular tone; it can best be explained as a response of the sensitized smooth muscle of the blood vessel wall to circulating vasoconstrictor substances.