RESPONSE OF VASCULAR STRIP PREPARATIONS TO NORADRENALINE AND TYRAMINE

Abstract

In order to investigate the sensitivity to norepinephrine the smooth muscle strip prepared from the following blood vessels were used: normal, reserpinized aorta of cats and rabbits; the carotid, renal, mesenteric, femoral, coronary artery, and jugular vein of pigs; umbilical artery of human placenta. The effect of tyramine was also studied on some of the above preparations. The ED50s were calculated from dose-response curves. The ED50 of norepinephine was increased by reserpine pretreatment in cats, while decreased in rabbits. Tyramine failed to produce any response in reserpinlzed aortic strips in doses enough to elicit contractions in normal preparations. The response to the amine reappeared by exposing the strip to submaximal doses of norepinephrine. Cocaine prevented this restoration. The norepinephrine induced relaxation of coronary strips was inhibited after the treatment with dichloroisoproterenol. When epinephrine was used a reversal of the response was observed. Tyramine produced a biphasic response: a contraction in the case of lowere doses and a relaxation for higher ones. The umbilical artery was still capable of responding to norepinephrine and tyramine even though the contraction was much less marked than that exerted by histamine and serotonin. Pure O2 bubbled into the bath solution produced an increase of the tone and CO2 caused a prompt relaxation of the strips accompanied by changes of the pH. Norepinephrine contents of blood vessels in pigs were determined in the following order of decreasing concentration: carotid, mesenteric, renal, coronary, femoral artery, and jugular vein. Little discernible correlation was demonstrated between sensitivity to norepinephrine and the amount of the amine found in blood vessels. It was considered that norepinephrine concentrations at the storage site are unlikely the unique factor in controlling susceptibity of the receptors.