High Intensity Exercise Training and Cardiac Beta-Adrenergic Responsiveness

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0896 We demonstrated previously that exercise training did not alter beta-adrenergic responsiveness in isolated hearts of either lean and obese rabbits (Carroll, MSSE, 2003;35:548). PURPOSE: To determine whether increased exercise intensity altered intrinsic beta-adrenergic responsiveness. In addition, we proposed that increased training intensity would reverse obesity-related reductions in beta-adrenergic responsiveness of isolated hearts. METHODS: Rabbits were assigned to lean control (LC, n = 7), lean exercise-trained (L-HI, n = 7), obese control (OC, n = 12), or obese exercise-trained (O-HI, n = 7) groups. Lean rabbits were fed a maintenance diet; obese rabbits were fed an ad lib high-fat diet. Exercise trained rabbits underwent a 12-wk progressive treadmill exercise program. Total work over 12 wks was 27% higher than the previous lower-intensity program. The Langendorff isolated heart method was used to study developed pressure, +dP/dt, and −dP/dt responses to increasing concentrations of isoproterenol (10−9−3×10−7 M). Concentration-response data were fit to a sigmoidal function using a four-parameter logistic equation. L-HI and O-HI were compared with respective controls and with animals trained under the lower intensity protocol (L-LO [n = 9] and O-LO [n = 8]) using a one-way ANOVA. RESULTS: +dP/dt and −dP/dt EC50 values were increased in L-HI and O-HI compared with respective LO and controls (see table) (*p ≤ 0.05; values expressed as mean ± SE). CONCLUSIONS: These data suggest that intrinsic responsiveness to beta-adrenergic stimulation may be reduced by high intensity training. Further, high intensity training did not reverse obesity-related alterations in beta-adrenergic responsiveness. Support by NIH HL04297 and HL64913Table: No Caption Available.