Contribution of adrenal norepinephrine output to increase aortic norepinephrine during carotid sinus reflex activation in anesthetized dogs.

Changes in circulating plasma catecholamine (CA: E, epinephrine; NE, norepinephrine; and DA, dopamine) concentrations in aortic (AO) blood were investigated in relation to variable rates of CA secretion from both adrenal (ADR) glands in response to bilateral carotid artery occlusion (BLCO) in vagotomized dogs anesthetized with sodium pentobarbital. During BLCO (3 min), AO systolic pressure (AP) increased along with significant increases in ADR-CA output, renal venous (RV) CA output, as well as in AO-E and NE concentrations. A ratio of NE:E in ADR venous and AO blood did not exceed 0.42 +/- 0.09 and 1.09 +/- 0.24 upon BLCO, respectively. In contrast, the NE:E ratio in RV blood increased significantly from 5.39 +/- 0.91 to 9.78 +/- 1.31. Following adrenalectomy (ADRX), the increase in AO-NE in response to BLCO was significantly attenuated by approximately 56%, but the increase in RV-NE output was not affected by ADRX. The results show that in vagotomized dogs, NE is co-released with E from the adrenal glands upon BLCO. The data also indicate that the increase in AO-NE concentration was dependent to a similar extent on the simultaneous increases in ADR-NE output and neuronal NE release. We conclude that under conditions where the sympathoadrenal system is activated, circulating plasma NE concentration may be significantly affected by an increase in ADR-NE output. Sympathetic neuronal contributions would, thereby, be overestimated in assessing overall sympathetic nerve activity by measuring circulating NE. NE concentrations in local venous effluent from individual organs may be more reliable estimates of the sympathetic nerve activity.