Regional XXXX production in @entity1 .

@entity1 @entity712 @entity4728 @entity5581 @entity750 @entity1130 @entity1063 @entity11460
Veno-arterial plasma concentration differences and regional organ plasma flows were used to quantify the relative amounts of @entity1130 ( @entity5581 ) contributed by various sites into the peripheral circulation. Positive venoarterial concentration gradients were found in the hepatosplanchnic, forearm, cardiac and jugular vessels in the healthy subjects. The renal circulation was determined to be the principal site of @entity5581 clearance, extracting 18 +/- 2 nmol/min. The gut was the greatest contributor to the total @entity5581 plasma pool with the relative contributions of the various organs being as follows: hepatosplanchnic organs 58%, skeletal muscle 26%, brain 6% and the heart 3%. The source of @entity5581 stemming from these regional beds remains unknown, it may derive from @entity750 taken up by and deaminated in ubiquitous endothelial cells, enterochromaffin cells of the gut, peripheral serotonergic nerves, @entity750 turnover in platelets or perhaps the metabolism of @entity750 taken up by sympathetic nerves. To test the latter hypothesis we examined 23 @entity1 with chronic @entity712 and 9 @entity1 with @entity4728 to investigate the possible effects of sympathetic nervous system overactivity and underactivity on peripheral @entity5581 production and plasma @entity5581 concentration. The resting arterial plasma @entity5581 concentration in the @entity712 @entity1 was increased three-fold. This elevated plasma @entity5581 concentration was attributable to an increased rate of whole body @entity5581 production. The arterial @entity5581 plasma concentration in the @entity11460 @entity1 was paradoxically elevated, being 70% greater than that of the healthy subjects. The increased @entity5581 plasma concentration in these @entity1 was accounted for by a reduction in @entity5581 plasma clearance. In all subjects studied there was a weak relationship only between total body @entity1063 spillover to plasma and the arterial @entity5581 plasma concentration. We found that in healthy subjects the overflow of @entity5581 into the hepatic vein was significantly related to the underlying degree of sympathetic activity. It can be concluded that @entity5581 is produced at a number of sites throughout the body with the arterial plasma concentration being dependent on both the level of production and plasma clearance. By far the majority of @entity5581 in plasma is derived from the gut with only minimal contribution from the brain.
