| pubmed-article:3565562 | pubmed:abstractText | To clarify the physiological role for the marked increases in circulating norepinephrine (NE) and epinephrine (E) that occur at birth, we performed graded infusions of NE and E in preterm (131 days) and full-term (142 days) fetal sheep. A variety of hemodynamic, metabolic, and endocrine responses to stepwise increases in plasma catecholamine levels were analyzed by computer-based graphical analysis of the dose-response curves. We determined the "threshold" value or minimum plasma concentration necessary to produce discernible effects. We observed increases in systolic blood pressure, diastolic blood pressure, and dP/dt beginning at plasma concentrations of 500-800 pg/ml of NE or E. In contrast, increases in plasma free fatty acid and glucose levels were observed at E concentrations as low as 50-100 pg/ml. Full-term animals had generally lower thresholds and higher peak responses than preterm animals. Because these thresholds for infused NE and E are well within the range of plasma catecholamine values seen at birth, these results underscore the importance of circulating catecholamines in the events of neonatal adaptation. | lld:pubmed |
