Maintained cerebral metabolic ratio during exercise in patients with β-adrenergic blockade

P>Background: Decreased cerebral metabolic ratio (CMR) [molar uptake of O(2) versus molar uptake of (glucose + 1/2 lactate)] during exercise is attenuated by intravenous administration of the non-selective beta-adrenergic receptor antagonist propranolol. We evaluated to what extent cirrhotic patients in oral treatment with propranolol are able to mobilize brain non-oxidative carbohydrate metabolism. Methods: Incremental cycle ergometry to exhaustion (86 +/- 4 center dot 2 W; mean +/- SD) was performed in eight cirrhotic patients instrumented with a catheter in the brachial artery and one retrograde in the right internal jugular vein. Healthy subjects form the control group. Results: In beta-blocked cirrhotic patients arterial lactate increased from 1 center dot 5 +/- 0 center dot 3 to 5 center dot 1 +/- 0 center dot 8 mM (P < 0 center dot 05) and the arterial-jugular venous difference (a-v diff) from -0 center dot 01 +/- 0 center dot 03 to 0 center dot 30 +/- 0 center dot 05 mM (P < 0 center dot 05) at rest and during exercise, respectively. During exercise the glucose a-v diff of 0 center dot 46 +/- 0 center dot 06 mM remained at a level similar to rest (0 center dot 54 +/- 0 center dot 03 mM) and at exhaustion the CMR was not significantly changed (5 center dot 8 +/- 1 center dot 1 versus 6 center dot 0 +/- 0 center dot 6). In controls, CMR decreased from 5 center dot 6 +/- 0 center dot 9 at rest to 3 center dot 4 +/- 0 center dot 7 (P < 0 center dot 05) during maximal exercise and at a lactate level comparable to that achieved by the patients it was 3 center dot 8 +/- 0 center dot 4. Conclusion: During exhaustive exercise in cirrhotic patients the CMR is maintained and a significant cerebral uptake of lactate is demonstrated. The data suggest that oral treatment with a non-selective beta-adrenergic receptor antagonist attenuates cerebral non-oxidative metabolism.