Fenoterol-induced changes of urine excretion, body weight, blood hematocrit, hemoglobin, total protein values and serum electrolyte levels in pregnant rabbits.
Infusion of the beta 2-sympathomimetic agonist fenoterol into pregnant rabbits at a dose of 20 micrograms/kg/min + 2.5 or 30 ml/h isotonic solution significantly reduced urine excretion. Body weight changes of animals infused with 20 micrograms/kg/min fenoterol + 2.5 or 30 ml/h isotonic solution were inversely correlated to the reduction of urine excretion. The urinary potassium excretion per 24 h was not significantly altered after the infusion of fenoterol + 2.5 or 30 ml/h isotonic solution. On the other hand, the urinary sodium excretion per 24 h was significantly decreased in animals infused with 20 micrograms/kg/min fenoterol + 30 ml/h isotonic solution. Infusion of 20 micrograms/kg/min fenoterol + 2.5 ml/h isotonic solution did not significantly change hematocrit, hemoglobin or total protein values. In contrast, increasing the volume of isotonic solution to 30 ml/h resulted in significantly decreased hematocrit, hemoglobin and total protein levels at 6, 12 and 24 h after starting infusion. Serum potassium concentrations were reduced at 2-24 h after infusion of 20 micrograms/kg/min fenoterol + 2.5 or 30 ml/h isotonic solution was started. The serum sodium concentrations did not change significantly during the infusion of 20 micrograms/kg/min fenoterol + 2.5 or 30 ml/h isotonic solution. While in animals infused with isotonic solution alone or with 20 micrograms/kg/min fenoterol + 2.5 ml/h isotonic solution the central venous pressure did not change significantly, it was strongly increased in animals infused with 20 micrograms/kg/min fenoterol + 30 ml/h isotonic solution at 12-24 h after start of infusion. The results of this study are discussed with respect to those obtained from pregnant women under tocolytic therapy and to the possible pathomechanism of the development of pulmonary edema.