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

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 +/- 4.2 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 1.5 +/- 0.3 to 5.1 +/- 0.8 mM (P<0.05) and the arterial-jugular venous difference (a-v diff) from -0.01 +/- 0.03 to 0.30 +/- 0.05 mM (P<0.05) at rest and during exercise, respectively. During exercise the glucose a-v diff of 0.46 +/- 0.06 mM remained at a level similar to rest (0.54 +/- 0.03 mM) and at exhaustion the CMR was not significantly changed (5.8 +/- 1.1 versus 6.0 +/- 0.6). In controls, CMR decreased from 5.6 +/- 0.9 at rest to 3.4 +/- 0.7 (P<0.05) during maximal exercise and at a lactate level comparable to that achieved by the patients it was 3.8 +/- 0.4.

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.