We examined the chronotropic and sympathoadrenal responses to a strenuous exercise in eight normal subjects receiving placebo and carteolol, a nonselective beta-adrenoceptor blocker. Plasma catecholamines were measured with high-performance liquid chromatography with electrochemical detection (HPLC-ECD). Mean plasma norepinephrine (NE) and epinephrine (E) concentrations attained at 0.5 and 2 min after exercise were significantly (p less than 0.001-0.05) greater in the carteolol trial than in the placebo trial and approached concentrations fairly similar to preexercise baseline values by 15 min after cessation of exercise in the two trials. The postexercise plasma NE and E concentration-chronotropic response relationships were shifted to the right in the carteolol as compared with the placebo phase. The maximal postexercise NE concentrations measured during the placebo trial correlated significantly with beta-adrenoceptor blockade (p less than 0.05, r = 0.74), whereas the relationship between E concentrations and beta-adrenoceptor blockade did not reach significant level in this small group of study subjects. The results suggest that beta-adrenoceptor blockade increases plasma concentrations of both NE and E during an earlier postexercise period and may cause a greater reflex sympathetic activation as compared with the adrenal response. However, the mechanism(s) remains unclear. Whether the exercise-induced NE rather than E would participate more predominantly in the chronotropic response to beta-adrenoceptor blockade requires further studies.
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