Local changes in venous tone due to bolus injections.

Abstract

Solutions were infused at a constant rate into ear veins of anaesthetized sheep and changes in venous tone were measured from changes in pressures in the infusion line when boluses of drugs and solutions were given. Approximately one in six veins was unresponsive. These appeared to be larger veins and the lack of response was probably due to greater blood flow causing appreciable dilution of the test solutions with blood. Most veins gave a transient venoconstriction to boluses of saline which had been made acid or alkaline and also to boluses of drugs such as aminophylline, calcium chloride, noradrenaline, metoclopramide, pentobarbitone, ethanol and thiopentone. Transient venoconstriction was usually repeatable and in proportion to the amount of solution or drug given, but sometimes the magnitude of the response changed unpredictably. Papaverine and nicotinamide usually reduced tone.