Peripheral Catecholaminergic Function Evaluated by Norepinephrine Measurements in Plasma, Extracellular Fluid, and Lymphocytes, from Nerve Recordings and Cellular Responses

Abstract

There is a close correlation between forearm venous plasma norepinephrine (NE) and muscle sympathetic nerve activity, as measured by microneurography. This has been observed not only at rest, but also during mental stress, hypoglycemia, and after raising and lowering arterial blood pressure, as well as during several pathophysiological states. Other than forearm organ release of NE can be calculated from the venous-arterial difference of NE corrected for the extraction of NE across the organ and from the blood flow to the organ. Studies in animals have indicated that the overflow is proportional to the impulse activity in sympathetic nerves to the organ, although this may not be true during all situations. The catecholamines may be derived from internalization of β 2 -adrenoceptors because there is a close correlation between cyclic adenosine monophosphate and the level of catecholamines in lymphocytes. Further studies of lymphocyte NE have demonstrated a marked difference in the NE content of lymphocytes from elderly smokers as compared with nonsmokers. It is well established that plasma NE increases with age. This phenomena is most pronounced in long-term smokers but also may be observed in nonsmokers. In lymphocytes, NE concentration was found to be increased in elderly nonsmokers but was markedly reduced in smokers. Further studies have shown that β 2 -adrenoceptor mRNA concentration is not reduced in long-term smokers, suggesting that the decrease in NE reflects a defective membrane function, especially of NK-cells, in long-term smokers.