[Cardiovascular action, placental passage, pharmakokinetics and metabolism of fenoterol in pregnant guinea pigs (authors transl)].

Cardiovascular action, placental passage and metabolism of fenoterol was studied in pregnant guinea pigs following either a single intravenous injection of 4.5 mug/kg or an infusion of 0.45 mug/kg per min. for 1 hour. After a single injection maternal heart rate increased from 212 to 248 beats/min. within the first minute retruning to basal levels after 35 min. Blood pressure decreased from 70 to 63 mm Hg within 6 min. Fetal heart rate remained unchanged during the first 15 min. but decreased lateron. Fenoterol was rapidly eliminated (t 1/2 = 36 min.) and metabolished. Metabolism consisted of a fast (t 1/2 =2,5 min.) and a slow (t 1/2 = 58 min.) component. Little radioactivity was found in fetal plasma following a single injection. Infusion of 0.45 mug/kg min. for 1 hour increased maternal heart rate from 208 to 234 beats/min. and decreased maternal blood pressure from 76 to 66 mg Hg within the first 10 min. Fetal heart rate remained unchanged for the first 15 min., but decreased from 249 to 219 beats/min. the second 15 min. Little radioactivity was found in fetal plasma also following infusion. Only 2 to 6 percent of the radioactivity (0.0lng/ml) were identified as unchanged fenoterol. The low lipophilic property of fenoterol may be responsible for the low permeability of the placental barrier.