Research on one group of nine anesthetized dogs pretreated with a-naphthyl-thiourea showed that doses of the β-sympathicomimetic fenoterol such as those normally administered in clinical tocolysis (2 µg/kg per minute) lead to significant fluid displacement to the extravascular space of the lung in the sense of a preclinical interstitial edema. In a second group (N=9) with the same pretreatment the addition of the β-1 selective blocker, metoprolol* (1.5 µg/kg per minute) served to antagonize the hemodynamic changes and possibly the increase of pulmonary capillary permeability induced by the β-mimetic. Fluid displacement into the interstitium of the lung was prevented by metoprolol. These observations corroborate the hypothesis that pulmonary edema occurring during tocolytic therapy is largely a result of the use of β-mimetics. In addition to its cardioprotective effect, the administration of the β-l selective blocker, metoprolol, may reduce the risk of the development of pulmonary edema in β-sympathicomimetic therapy for premature labor.
© 1986 The American College of Obstetricians and Gynecologists