[Effect of the beta-blocker metoprolol on the cardiovascular system and plasma catecholamines of the fetus in normoxia and acute hypoxia--animal experiment studies].

Metoprolol, a beta 1 blocking agent, is being used with increasing frequency during pregnancy for treatment of disorders such as hypertension or beta-mimetic induced tachycardia. Since it is well documented that beta-blocking agents are able to cross the placenta, the question arises whether these drugs have any adverse effect on the fetal metabolic or cardiovascular system. It was the aim of this animal experimental study to investigate the following questions: 1. Does metoprolol exert a negative influence on fetal metabolic and cardiovascular functions during normoxia? 2. Is the fetal reaction to an acute short period of hypoxemia altered by metoprolol? To answer these questions, experiments were carried out in 6 pregnant sheep at 110-130 days of gestation. In 8 experiments metoprolol was infused into a fetal vein in increasing dosage (0,04-0,32 mg/min). In a second series of experiments (n = 8), an acute hypoxemia was induced by complete reduction of uterine blood flow for 1 minute, and the results obtained with or without metoprolol were compared. Metoprolol does not exert a negative influence on fetal oxygenation, acid-base balance, lactate concentration and blood pressure, although the metoprolol concentration measured in fetal plasma was relatively high (two - to threefold above therapeutic metoprolol levels). Thus, definitive adverse effects on the fetus induced by metoprolol are not recognizable. The fetal sympathoadrenal reaction to an acute hypoxemia, as measured by the concentration of the free catecholamines epinephrine, norepinephrine and dopamine in the fetal plasma, is also unchanged by metoprolol.(ABSTRACT TRUNCATED AT 250 WORDS)