NEURONAL METABOLISM OF CATECHOLAMINES IN PITHED AND ELECTRICALLY STIMULATED RATS

The aim of the present study was to investigate a possible physiologic al equilibrium, assessed by statistically significant correlations, be tween pre-junctional mechanisms that regulate both release and reuptak e of norepinephrine (NE) and post-junctional mechanisms that participa te in the regulation of the smooth muscle cell and thus in the regulat ion of blood pressure, This study was carried out in pithed and electr ically stimulated (2.5 Hz) rats to obtain an experimentally controled release of NE. A radio-enzymatic assay was used to measure plasma conc entrations of NE, index of NE release and levels of its deaminated met abolites 3,4-dihydroxyphenyl glycol (DHPG) and 3,4-dihydroxymandelic a cid (DOMA). DHPG is known to be an index of NE reuptake and deaminatio n while the physiological significance of DOMA remains unclear. Our re sults demonstrate a statistically significant correlation between plas ma NE concentration and blood pressure on one hand, and between plasma NE and DHPG concentrations on the other. These correlations support o ur working hypothesis and suggest a physiological equilibrium between pre- and post-junctional phenomena in the control of blood pressure. D uring 2.5-Hz stimulation, plasma DHPG concentration was increased whil e plasma DOMA remained unchanged. This is consistent with activation o f the reduction pathway and the consequent formation of DHPG by aldehy de reduction, while the oxidation pathway mediated by aldehyde dehydro genase does not appear to play a major role in the presynaptic metabol ism of reuptaken NE in the present experimental conditions. Further in vestigations are needed to investigate the apparent dissociation betwe en the two enzymatic pathways involved in the second step of the deami nation process.