Abstract
To study the direct effect of tolazoline (T) in a high resistance pulmonary vascular bed, we infused T in nine chronically prepared fetal sheep with and without calcium channel blockade. An electromagnetic flow transducer placed around the left pulmonary artery (LPA) measured blood flow to the left lung (QL). Catheters placed in the left atrium (LA), main pulmonary artery, aorta and amniotic cavity measured pressure. An infusion catheter was placed in the LPA. After obtaining baseline measurements for 30 minutes, T (4.5 mg/hour) was continuously infused into the LPA for 90 minutes. After an increase over the first 30 minutes, QL decreased toward the control value. Throughout the infusion, the concentration of T steadily increased in the LA (peak=0.53 ugm/ml). When verapamil (V) was infused with T, the increase in QL was sustained throughout the 90 minute infusion period.
There were no significant changes in heart rate or pressures. V alone had no effect on QL. We conclude that T dilates the pulmonary vascular bed in the fetal sheep, but adaptation occurs despite increasing drug levels. The adaptive response to T may be a calcium dependent mechanism.
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Abman, S., Accurso, F., Ward, R. et al. 227 ADAPTATION OF FETAL PULMONARY BLOOD FLOW TO LOCAL INFUSION OF TOLAZOLINE. Pediatr Res 19, 148 (1985). https://doi.org/10.1203/00006450-198504000-00257
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DOI: https://doi.org/10.1203/00006450-198504000-00257