Urinary excretion, osmolarity and electrolytes after bolus-injection of fenoterol in female rabbits.

The effects of bolus injections of 1.0-80.0 micrograms/kg body weight fenoterol on urinary excretion, osmolarity and electrolytes were studied in unanesthetized, water-loaded rabbits. In animals infused initially with isotonic solution over 2 h with 60 ml/h and thereafter over 10 h with 45 ml/h, urine excretion was 538 ml/12 h, sodium excretion was 65.4 mmol/12 h, and potassium excretion was 4.8 mmol/12 h. In animals injected with 5.0-80.0 micrograms/kg body weight fenoterol, a strong antidiuresis occurred, lasting for 2 (10.0 micrograms/kg) to 4 h (80.0 micrograms/kg). Due to the strong antidiuresis, urinary osmolarity was significantly elevated for 2 (10.0 micrograms/kg) to 3 h (80.0 micrograms/kg). The changes of sodium excretion after fenoterol injection were very similar to those of urine excretion. Maximum reduction of sodium excretion was found after injection of 10.0-80.0 micrograms/kg body weight fenoterol, the effect lasting for 1 h (10.0 micrograms/kg) to 4 h (80.0 micrograms/kg). Potassium excretion was significantly reduced after injection of 5.0-80.0 micrograms/kg body weight fenoterol. In contrast to all the other parameters measured, potassium excretion remained significantly reduced until the end of the infusion period in animals treated with 10.0-80.0 micrograms/kg body weight fenoterol and was not dose dependent. Our data presented in this work extend earlier findings in the rabbit in that bolus injection of fenoterol also results in a drastic decrease of urine and electrolyte excretion. The results are discussed with special reference for the management of acute fetal distress with betamimetics and to the development of pulmonary edema that has been shown to occur under therapy with betamimetics on both female rabbits and humans.