Isometric exercise before and after beta-receptor blockade with propranolol and mepindolol sulfate

The effect of isometric exercise on hemodynamic parameters before and after beta blockade were investigated in two groups of six male volunteers, ages 25-28 years. On the basis of a randomized scheme, the subjects received either 15 mg propranolol i.v. or 0.5 mg mepindolol sulfate i.v. Cardiac output (CO) was determined by means of the Swan-Ganz thermodilution technique, and blood pressure was measured invasively in the radial artery. Analysis of the results pointed to the following conclusions. Isometric contraction brings about a reflex constriction of arterial and venous vessels, and thus an increase in blood pressure, pulmonary artery wedge pressures (PAWP) and CO, as well as a reduction in stroke volume (SV). The circulatory reflex mechanism operative during isometric exercise cannot be significantly influenced by beta blockade with propranolol or mepindolol sulfate. The increase in heart rate during isometric exercise is therefore unlikely to be the result of sympathetic activation, but rather of other (vagal?) reflex mechanisms.