Effect of autonomic blockade on pressor responses to vasopressin in pregnant rats.

OBJECTIVE

We tested the hypothesis that gestational changes in reflex neural control of the heart and vasculature contribute to altered cardiovascular responses to vasopressin during pregnancy.

STUDY DESIGN

Changes in mean arterial pressure, cardiac output, total peripheral resistance, and heart rate were measured in response to constant infusion of arginine vasopressin (0.15 to 2.5 mU/kg/min) in conscious pregnant and virgin rats (n = 9) with total autonomic blockade plus restoration of baseline hemodynamics by norepinephrine infusion.

RESULTS

Resting cardiac output was 40% higher and total peripheral resistance 30% lower in pregnant animals (p < 0.01). Constant infusion of arginine vasopressin evoked equivalent changes in mean arterial pressure in both groups, but the respective contributions of cardiac output and total peripheral resistance to mean arterial pressure differed between groups. Cardiac output was unchanged and the increase in total peripheral resistance was significantly blunted in pregnant vs virgin rats during arginine vasopressin infusion. Control data in nonblocked revealed similar pressor responses to arginine vasopressin in gravid compared with virgin rats but no differences in the contributions of cardiac output and total peripheral resistance to the change in mean arterial pressure.

CONCLUSION

These findings suggest that neural modulation of arginine vasopressin-induced hypertension is altered during pregnancy and are consistent with a reduction in intrinsic vascular sensitivity to arginine vasopressin during gestation.