EFFECT OF ADRENALINE AND VASOPRESSIN ON THE UTERINE RESPONSE TO OXYTOCIN IN CONSCIOUS RABBITS

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Abstract
The effect of simultaneous injections of adrenaline and oxytocin and of vasopressin and oxytocin upon the uterus of intact, unanaesthetized puerperal rabbits has been studied using intrauterine balloons which could be left in situ for several days. Moderate doses of adrenaline (5-25 μg) did not inhibit the effect of simultaneously administered oxytocin on the uterus. The effect of oxytocin appears superimposed upon the uterine response to adrenaline. When low doses of oxytocin are used a delay of the oxytocic effect occurs. Vasopressin (lysine-8-vasopressin) in a proportion up to 1:1 had no effect or only slightly modified the effect of simultaneously administered oxytocin. No potentiation of the response to oxytocin was observed but some incoordination of the contractions as well as slight increase in uterine tone occurred in late puerperium. When present in a proportion of 10:1, vasopressin completely prevented the effect of oxytocin, the uterine response being similar to that seen after the same dose of vasopressin alone, namely a long lasting inhibition of uterine motility after a short initial excitatory period. However, more than 50 mU of vasopressin were necessary to elicit any inhibitory effect. Even larger doses of vasopressin (250 mU) that alone or together with ten times less oxytocin would have caused a strong inhibition, did not affect the response to equal doses of oxytocin.