Chappell B A, Padbury J F, Habib D M, Martinez A M, Thio S L, Burnell E E, Humme J A
Department of Pediatrics, Harbor-UCLA Medical Center, Torrance 90509.
Pediatr Res. 1991 Jan;29(1):93-7. doi: 10.1203/00006450-199101000-00018.
The lungs play an important role in the metabolism of vasoactive substances including endogenous amines. The role of pulmonary clearance of circulating norepinephrine has not been well defined in the young lamb (7-8 d of age). Using radiolabeled tracer norepinephrine in acutely instrumented lambs, we determined the in vivo pulmonary clearance and spillover rate of norepinephrine under baseline and hypoxic conditions. The fractional extraction of norepinephrine, the percent removed on a single pass through the pulmonary circulation, was 23 +/- 2%. The corresponding pulmonary clearance rate was 61 +/- 10 mL/kg/min and the net pulmonary norepinephrine removal rate was 0.41 +/- 0.14 nmol/kg/min. This clearance represented over 70% of whole body norepinephrine clearance. The spillover of synaptic norepinephrine was 0.22 +/- 0.13 nmol/kg/min. During hypoxia, animals showed significant increases in pulmonary artery pressure and resistance. Fractional extraction and norepinephrine decreased to 16 +/- 3%, p less than 0.005. Pulmonary clearance decreased to 31 +/- 7 mL/kg/min, and net pulmonary norepinephrine removal rate decreased to 0.27 +/- 0.07 nmol/kg/min. These results demonstrate that pulmonary clearance plays a significant role in norepinephrine clearance in 1-wk-old lambs. Alteration of norepinephrine clearance during physiologic states such as hypoxia may be important in the pathophysiology of altered pulmonary vascular resistance in newborn animals.
肺在包括内源性胺类在内的血管活性物质代谢中发挥着重要作用。循环去甲肾上腺素的肺清除作用在幼龄羔羊（7 - 8日龄）中尚未得到很好的界定。我们在急性插管的羔羊中使用放射性标记的示踪去甲肾上腺素，测定了基线和低氧条件下去甲肾上腺素的体内肺清除率和溢出率。去甲肾上腺素的分数提取率，即单次通过肺循环时被清除的百分比，为23±2%。相应的肺清除率为61±10 mL/kg/min，肺去甲肾上腺素净清除率为0.41±0.14 nmol/kg/min。这种清除率占全身去甲肾上腺素清除率的70%以上。突触去甲肾上腺素的溢出率为0.22±0.13 nmol/kg/min。在低氧期间，动物的肺动脉压和阻力显著增加。分数提取率和去甲肾上腺素降至16±3%，p<0.005。肺清除率降至31±7 mL/kg/min，肺去甲肾上腺素净清除率降至0.27±0.07 nmol/kg/min。这些结果表明，肺清除在1周龄羔羊的去甲肾上腺素清除中起重要作用。在诸如低氧等生理状态下去甲肾上腺素清除的改变在新生动物肺血管阻力改变的病理生理学中可能很重要。
