The effect of beta-receptor-stimulating agents on the utero-placental blood flow

The influence of salbutamol, a beta-2-receptor-stimulating agent, on the blood flow through the utero-placental unit was evaluated in the human. Serial placenta scintigrams were analysed quantitatively, after injection of 0.5 mCi Indium-113m, by means of a gamma-camera connected on line to a computer. The examinations were performed in the third trimester of pregnancy. No sedation was used. Uterine contractions were not present. Salbutamol caused an increase in activity over the placental region, corresponding to a 15% increase in blood volume. The rise time of the initial phase of isotope accumulation (calculated from 5 to 95% of final activity) was prolonged by 100% during salbutamol infusion. As the rise time is proportional to the volume/flow ratio of blood in the uteroplacental region, our data indicate that salbutamol infusion causes a decrease in blood flow in the absence of uterine contractions.