Effects of the tocolytic agent fenoterol on body weight, urine excretion, blood hematocrit, hemoglobin, serum protein, and electrolyte levels in nonpregnant rabbits.

Infusion of an isotonic solution and increasing doses of the beta 2-sympathomimetic agonist fenoterol (0.6, 20, or 80 micrograms/kg/min) into female rabbits led to a reduction in urine excretion and a concomitant dose-dependent increase in body weight. Although an infusion at 2.5 ml/hr of an isotonic solution that contained 0.6 or 20 micrograms/kg/min of fenoterol did not significantly change the hematocrit, hemoglobin, or serum protein levels, they were significantly decreased by a similar infusion that contained 80 micrograms/kg/min of fenoterol and by giving 20 ml/hr of an isotonic solution that contained 0.6, 20 or 80 micrograms/kg/min of fenoterol. The central venous pressure remained unchanged in animals that received 2.5 ml/hr of an isotonic solution alone or in combination with 0.6 to 80 micrograms/kg/min of fenoterol. It was significantly elevated in animals treated with 30 ml/hr at similar doses. These data support our hypothesis that the development of pulmonary edema which has been reported with the use of tocolytic therapy is mainly due to hypervolemia related to the antidiuretic effect of the beta 2-sympathomimetics. The intravascular hypervolemia leads to an increased fluid content of the lung and may explain the development of pulmonary edema.