Pediatric research
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A model of patent ductus arteriosus in premature lambs was created to study the relative importance of beta-adrenoreceptor stimulation and increased myocardial contractility. In 39 fetal lambs (133 +/- 2, +/- SD days gestation, term 145 days), the ductus arteriosus was infiltrated with formalin, and a snare was placed around it to regulate its patency. One day later, the lambs were delivered, given sheep surfactant, paralyzed, and mechanically ventilated. ⋯ The left atrium was paced in both control and propranolol-treated lambs. When the ductus was closed, propranolol significantly decreased stroke volume and peak dP/dt without changing left ventricular end-diastolic pressure or systemic vascular resistance. During a saline volume load (50 ml/kg over a 3-min period), propranolol-treated lambs had a reduced stroke volume and peak dP/dt despite similar values of left ventricular end-diastolic pressure and resistance as those of control lambs.(ABSTRACT TRUNCATED AT 250 WORDS)