Thermoregulation in mildly hypertensive men during beta-adrenergic blockade.

Nonselective beta 1,beta 2-adrenergic blockade (nBB) reduces the cutaneous blood flow and sweating responses to exercise in normotensive men and results in a relative increase in heat storage. To determine whether hypertensives incur similar problems in thermoregulation, we studied six mildly hypertensive men during 30 min of cycle ergometer exercise at 60% maximum O2 uptake at 22 degrees C. Each subject ingested either propranolol (Pr, 80 mg; nBB), metoprolol (Me, 50 mg; cardioselective, sBB), pindolol (Pi, 5 mg; nBB), or placebo (Pl) capsules 2 h before exercise in a double-blind crossover design. Steady-state exercise heart rate, systolic blood pressure (SBP), and cardiac output (Q) were reduced from means (+/- SD) of 134 +/- 7 beats.min-1, 181 +/- 5 mm Hg, and 14.5 +/- 0.9 l.min-1, respectively, with Pl to 107 +/- 3 beats.min-1, 159 +/- 7 mm Hg, and 12.7 +/- 1.1 l.min-1, respectively, with beta-blockade (BB, average of Pr, Me, and Pi) (P less than 0.05). During nBB, we found 1) a decrease in peak forearm blood flow (FBF) and 2) a reduction in the slopes of the FBF-esophageal temperature (Tes) and local chest sweat rate-Tes (Pr only) relationships. These resulted in a trend toward higher Tes at 30 min of exercise. Forearm vascular resistance was increased with nBB but not sBB, demonstrating a relative cutaneous vasoconstriction during nBB. Since nBB and sBB produced similar effects on the central circulatory variables (SBP and Q) but had different effects on FBF and FVR, our data do not support a role for baroreflexes in the altered control of FBF during BB.