Plasma dose-response studies with noradrenaline and adrenaline in man.

Graded infusions of noradrenaline (n = 25) and adrenaline (n = 30) were performed in normal human subjects. Plasma noradrenaline thresholds for biologic effects were 1,500-2,000 pg/ml, higher than levels achieved under common physiologic conditions. Thus, noradrenaline functions primarily as a sympathetic postganglionic neurotransmitter although it may also function as a hormone in some physiologic and many pathophysiologic states. Plasma adrenaline thresholds were lower - approximately 100 pg/ml for cardiac chronotropic, systolic pressor and lipolytic effects, 150-200 pg/ml for hyperglycemic, glycolytic, ketogenic and diastolic depressor effects and greater than 400 pg/ml for suppression of insulin secretion. Since these levels lie within the physiologic range, adrenaline is likely to be a biologically important regulatory hormone. Further, noradrenaline and adrenaline were found to accelerate their own plasma metabolic clearance rates.