title: Thresholds for physiological effects of plasma catecholamines in fetal sheep.
abstract: 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.
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D001784:Blood Gas Analysis; D001786:Blood Glucose / Q000378:metabolism; D002395:Catecholamines / Q000494:pharmacology / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005865:Gestational Age; D005934:Glucagon / Q000097:blood; D006439:Hemodynamics / Q000187:drug effects; D012756:Sheep / Q000196:embryology* / Q000502:physiology
chemical_list: D001786:Blood Glucose; D002395:Catecholamines; D005230:Fatty Acids, Nonesterified; D005934:Glucagon