SPLANCHNIC GLUCOSE PRODUCTION AND BLOOD FLOW DURING EXERCISE: THE RENIN-ANGIOTENSIN SYSTEM 247

Abstract

The importance of the renin-angiotensin system for liver glucose output and flow was tested in 8 male subjects (age:25 +/- 1 yrs (mean and SE), Vo2max:4.0+/- 0.2 l/min). They performed semisupine cycling for 40 min at 50% Vo2max and 30 min at 70%Vo2max without (C) or with i.v. administration of an angiotensin-converting-enzyme inhibitor (10mg enalapril) (ACE) prior to exercise. Whole body glucose turnover was measured by primed constant infusion of 3H-glucose, and splanchnic substrate exchange and flow was measured by constant ICG-infusion and blood sampling from arterial and hepatic venous catheters. During exercise heart rate, mean arterial blood pressure, arterial lactate and RER increased similarly in drug and control studies (p>0.05). Hepatic glucose production increased during exercise similar in both experimental situations measured with 3H-glucose isotope dilution as well as with arterial and hepatic vein measurements (2.11 +/- 0.23 mg/min/kg to 7.29+/- 1.03 (ACE) and 2.21 +/- 0.18 to 7.82 +/- 0.70 (C)). Glucose production matched peripheral glucose uptake, and in both ACE and C arterial glucose did not change significantly during exercise (5.27 +/- 0.10 mM to 4.71 +/- 0.28(ACE) and 5.22 +/- 0.11 to 4.69 +/- 0.23 (C)). Splanchnic blood flow fell by 10% during moderate and 45% during intense exercise in both ACE (1.64 +/- 0.22 l/min to 1.52 +/- 0.20 (35 min) and 0.92 +/- 0.12 (65min)) and C (1.55 +/- 0.20 to 1.36 +/- 0.18 and 0.81 +/- 0.13) experiments. In conclusion Inhibition of the renin-angiotensin system does not influence neither the rise in hepatic glucose production nor the reduction in splanchnic flow during moderate or intense dynamic exercise in humans.