Uteroplacental blood flow during alkalosis in the sheep.

Uteroplacental blood flow was measured by the radioactive-microsphere technique in eight near-term pregnant ewes during a normal control period and during maternal metabolic alkalosis. All measurements were made on awake, unanesthetized animals. Alkalosis, defined for this study as an arterial pH of 7.60 or greater, was produced by the oral administration of sodium bicarbonate, 3 g/kg body wt. The rise in pH thus produced was unaccompanied by significant changes in systemic arterial blood pressure and cardiac output, while maternal arterial Pco2 rose slightly from control levels. Cotyledonary blood flow declined from a control value of 1,177 ml/min to 1,025 ml/min during alkalosis. This decline of 13 percent in cotyledonary blood flow is significant (P smaller than 0.002). Blood flow to the remaining uterine tissue, or noncotyledonary uterus, did not change with alkalosis, being maintained at approximately 195 ml/min. It is concluded that maternal alkalosis, unaccompained by major changes in Pco2 and systemic arterial pressure, causes a small increase in the resistance of the uteroplacental circulation.