Contribution of lungs to desipramine-induced changes in whole body catecholamine kinetics in newborn lambs.

To characterize pulmonary and total body norepinephrine and epinephrine kinetics in the immediate newborn period, the effects of desipramine were studied in six fetal lambs chronically instrumented at 133-134 days gestation (term 147 days) and delivered 1 wk later by cesarean section under spinal anesthesia. Norepinephrine and epinephrine kinetics were determined with isotope dilution methodology 4 h after birth and repeated 30 min after desipramine (2 mg/kg iv). At baseline, the lungs accounted for 35 ± 10 and 47 ± 13% of whole body norepinephrine clearance (93 ± 8 ml ⋅ min-1 ⋅ kg-1) and spillover (188 ± 29 ng ⋅ min-1 ⋅ kg-1) and 15 ± 2 and 19 ± 7% of whole body epinephrine clearance (82 ± 4 ml ⋅ min-1 ⋅ kg-1) and release (22.7 ± 2.7 ng ⋅ min-1 ⋅ kg-1), respectively. Desipramine decreased pulmonary norepinephrine and epinephrine clearance and spillover to near-zero levels, whereas whole body norepinephrine clearance fell by 51 ± 3% ( P < 0.001), norepinephrine spillover by 54 ± 6% ( P < 0.005), epinephrine clearance by 30 ± 6% ( P < 0.01), and epinephrine spillover by 34 ± 11% ( P < 0.05). These results indicate that, in the immediate newborn period, pulmonary removal and release of norepinephrine and epinephrine is mediated by a desipramine-sensitive process that accounts for a major portion of associated reductions in whole body norepinephrine and epinephrine clearance and release.