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Department of Molecular Physiology and Biophysics, Vanderbilt University Schoool of Medicine, Nashville, Tennessee 37232
Received 20 August 1996; accepted in final form 4 December 1996.
Coker, Robert H., Mahesh G. Krishna, D. Brooks Lacy, Eric J. Allen, and David H. Wasserman. Sympathetic drive to liver and
nonhepatic splanchnic tissue during heavy exercise. J. Appl. Physiol. 82(4): 1244-1249, 1997.
The
contribution of sympathetic drive and vascular catecholamine delivery
to the splanchnic bed during heavy exercise was studied in dogs that
underwent a laparotomy during which flow probes were implanted onto the
portal vein and hepatic artery and catheters were inserted into the
carotid artery, portal vein, and hepatic vein. At least 16 days after
surgery, dogs completed a 20-min heavy exercise protocol (mean work
rate of 5.7 ± 1 miles/h, 20 ± 2% grade). Arterial epinephrine
(Epi) and norepinephrine (NE) increased by ~500 and ~900 pg/ml,
respectively, after 20 min of heavy exercise. Because Epi is not
released from the splanchnic bed and because Epi fractional extraction
(FX) = NE FX, NE uptake by splanchnic tissue can be calculated despite simultaneous release of NE. Basal nonhepatic splanchnic (NHS) FX
increased from a basal rate of 0.52 ± 0.09 to a peak of 0.64 ± 0.05 at 10 min of exercise. Hepatic Epi FX increased from
a basal rate of 0.68 ± 0.10 to 0.81 ± 0.09 at 20 min of exercise. Even though NHS extraction of Epi reduced portal vein
Epi levels by ~60%, the release of NE from NHS tissue maintained
portal vein NE at levels similar to those in arterial blood. NHS NE
spillover increased from a basal rate of 5.7 ± 1.4 to 11.7 ± 2.8 ng · kg
1 · min
1
at 20 min of exercise. Hepatic NE spillover increased from a basal rate
of 5.0 ± 1.2 ng · kg
1 · min
1
to a peak of 14.2 ± 2.8 ng · kg
1 · min
1
at 15 min of exercise. These results show that
1) approximately two- and threefold
increases in NHS and hepatic NE spillover occur during heavy exercise,
demonstrating that sympathetic drive to these tissues contributes to
the increase in circulating NE; 2) the high catecholamine FX by the NHS tissues results in an Epi level at
the liver that is considerably lower than that in the arterial blood;
and 3) circulating NE delivery to
the liver is sustained despite high catecholamine FX due to
simultaneous NHS NE release.
catecholamines; fractional extraction; uptake; spillover
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