[Dosage related effect of fenoterol on fetal hemoglobin oxygen affinity (author's transl)]

Fenoterol induced displacements of the fetal oxygen dissociation curve were investigated in animal experiments by determining the oxygen halfsaturation pressure (P 50). At term pregnant rabbits were infused intravenously over 3 hours with an increasing Fenoterol dosis (10 to 30 microgram/kg/min) up to a dosis level which produced complete labour inhibition. By cesarean section fetal aortic blood was collected and the oxygen halfsaturation pressure (P 50) was determined as described by Lichtman et al. (14). All P 50 values were corrected to so-called standard conditions (pH: 7.4; PCO2: 40 mmHg; t: 37 degrees C). Likewise, in a second series P 50 values were measured in newborn rabbits which received Fenoterol subcutaneously as a single shot injection. In the first series standardized P 50 significantly fell from 20.9 to 15.0 mmHg and in the second series it fell from 20.9 to 14.4 mmHg. This raised oxygen hemoglobin affinity, i.e. leftward shift of the fetal oxygen dissociation curve, is probably due to a Fenoterol induced diminution of the red cell 2.3-DPG concentration. In all cases of severe fetal hypoxia a beneficial effect on O2-transport is discussed whereas at normoxia or mild hypoxia a rightward shift of the oxygen dissociation curve would be more favourable.