Cardiovascular responsiveness to arginine vasopressin in water-loaded and sodium-depleted pregnant and non-pregnant sheep.

1. In conscious ewes pregnancy was associated with a significantly increased heart rate and cardiac output, while mean arterial pressure (MAP) and stroke volume were unchanged. 2. The present study examines the effect of arginine vasopressin (AVP) infused at 0.3, 1, 3.0, and 10 micrograms/h, into water-loaded and sodium-depleted ewes, either non-pregnant or during the last third of gestation. 3. In the water-loaded state, MAP rose significantly at the lowest rate of infusion in both pregnant and non-pregnant ewes. Bradycardia occurred first at 0.3 micrograms/h in the pregnant ewes but not until 3.0 micrograms/h in the non-pregnant animals. 4. In sodium deficiency there was no increase in MAP at any rate of infusion in either group. Bradycardia occurred in both groups at 1 microgram/h. 5. This study shows that the pressor effects of AVP are unchanged by pregnancy. However, pregnant ewes are more sensitive to AVP-induced bradycardia when the ewes are water-loaded.