[Relationships between noradrenaline kinetics and hemodynamic response under physical stressors]

Noradrenaline (NA) levels in blood and urine were measured in 7 male adults before, during, and after a mild ergometer exercise. Blood pressure (BP) and heart rate (HR) were continuously recorded during all of their stages. Blood specimens were obtained with a catheter introduced into the antecubital vein and plasma NA (PNA) level was measured with high performance liquid chromatography (HPLC) with electrochemical detection. NA and vanillylmandelic acid (VMA) levels in urine were measured by HPLC. The sequential changes of BP, HR, PNA, UNA, and VMA were simulated in a mathematical models of multiexponential functions as expressed by: sigma Aiexp(-Bit)(t; time). The present study suggests that the sequential changes of HR and systolic blood pressure (SBP) reflected the amount of NA secreted at sympathetic nerve endings on the effectors subserving HR and SBP changes, and therefore they were related to overflow of NA into plasma and urine, and also that of VMA into urine. The net NA levels at the nerve endings, as a result of NA kinetics, could be estimated from SBP and HR and could determine the rate of overflow of NA into plasma and urine. It was also revealed that the levels of SBP, PNA, UNA and urine volume immediately before the exercise were closely related to the rate of the diffusion. The rate of diffusion of NA into urine decreased to some extent as that of NA into plasma increased, but the rate of diffusion turned to an increase, when the latter exceeded a critical level.