Effect of isoproterenol on uterine blood flow and cardiac output distribution in pregnant guinea pigs

Abstract The effects of isoproterenol, 0.05 μg · min −1 · kg −1 infused intravenously for 2 hours, on cardiac output distribution and uteroplacental blood flow were studied in six chronically catheterized guinea pigs between 60 and 68 days of pregnancy. Isoproterenol caused marked cardiac stimulation: Cardiac output was increased by 41%, of which 70% was distributed to the carcass and gastrointestinal tract. Absolute placental blood flow remained essentially unchanged, but the placental fraction of cardiac output decreased from 16% to 11%. Myometrial blood flow increased by 72%. Uteroplacental vascular resistance did not change significantly. In the guinea pig in late pregnancy β-adrenergic receptors are present in the myoendometrial vessels but could not be demonstrated in the maternal vessels supplying the placenta.