Nifedipine does not adversely affect uteroplacental blood flow in the hypertensive term-pregnant rat

The short-term effect of the calcium channel blocker, nifedipine, on maternal hemodynamics and organ perfusion was investigated in 12 hypertensive term-pregnant, spontaneously hypertensive rats by means of the radioactive-labeled microsphere technique. The normal fall in blood pressure during pregnancy was prevented by reducing litter size to two conceptuses on day 7 of gestation. Nifedipine (200 micrograms/kg) effectively lowered mean arterial pressure 25% by decreasing total peripheral resistance 38%. Cardiac output was increased 15%. Blood flows to the splanchnic region and the reproductive organs were increased after nifedipine administration. The increase in blood flow to the reproductive organs was the result of increased ovarian and uterine wall perfusion caused by large reductions in vascular resistances. Placental blood flow was not significantly altered, but resistance was decreased. Thus, the use of nifedipine to lower maternal blood pressure in pregnancy complicated by extreme hypertension does not necessarily decrease uteroplacental perfusion.