Effect of pregnancy in the rabbit on the pressor response to angiotensin and noradrenaline

SUMMARY 1. The pressor responses to angiotensin II injections of 29, 117 and 468 pmol/kg and infusion at 54 pmol/kg per min were compared in near-term pregnant and matched non-pregnant rabbits. The responses to noradrenaline injections of 652, 2608 and 10 432 pmol/kg and infusion at 1185 pmol/kg per min were similarly compared. 2. At all doses of angiotensin and noradrenaline, whether by injection or infusion, the response of the pregnant animals was significantly greater. However the control arterial pressures of the pregnant rabbits were lower and fell in a range where the baroreceptor reflex might be less effective. Thus less efficient buffering could contribute to the greater response to the vasoconstrictor agents. 3. To test the effect of pregnancy on the vascular response to angiotensin and noradrenaline when reflex and central effects were excluded, hexamethonium was used to produce autonomic ganglion blockade. The response to both vasoconstrictors was now less in the pregnant rabbits than in the non-pregnant. 4. Thus in assessing the effects of pregnancy on the responses of the rabbit to angiotensin and noradrenaline the effect of pregnancy on mean blood pressure must be taken into account, since this can influence the extent to which the arterial baroreceptors may modulate the response.