A comparison of two exercise training programs on cardiac responsiveness to beta-stimulation in obesity.
We demonstrated previously that exercise training did not restore normal cardiac beta-adrenergic responsiveness in obese rabbits. This study tested the hypothesis that an increased training volume was required to attenuate obesity-related reductions in isolated heart responsiveness to isoproterenol. Female New Zealand White rabbits were divided into lean control, lean exercise-trained, obese control, and obese exercise-trained groups. For the exercise-trained groups, total treadmill work over 12 weeks was increased 27% when compared with lean and obese animals trained with lower total training volume. After 12 weeks, Langendorff isolated hearts were used to study developed pressure, +dP/dt(max), and -dP/dt(max) responses to isoproterenol (10(-9) - 3 x 10(-7) M). Concentration-response data were fit to a sigmoidal function using a four-parameter logistic equation. Controls were compared with animals trained under the low- and high-training volume programs using one-way analysis of variance and Tukey's post-hoc test; separate analyses were conducted for lean and obese rabbits. In both lean and obese groups trained under the high-training volume program, EC50 values for +dP/day(tmax) and -dP/dt(max) were higher compared with same-weight controls and animals trained under the low-training volume program, indicating that contractility and relaxation responsiveness to isoproterenol was reduced by the higher training volume. Therefore, these data indicate that increased training volume failed to attenuate obesity-related decrements in isolated heart responsiveness to beta-adrenergic stimulation and caused reduced sensitivity to isoproterenol in both lean and obese animals.
Carroll
Joan F
JF
Department of Integrative Physiology, University of North Texas Health Science Center, 3500 Camp Bowie Boulevard, Fort Worth, TX 76107-2699, USA. jcarroll@hsc.unt.edu
Thaden
Jeremy J
JJ
Wright
Allison M
AM
D000318:Adrenergic beta-Agonists / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure; D001823:Body Composition; D004305:Dose-Response Relationship, Drug; D005081:Exercise Therapy; D005260:Female; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006728:Hormones / Q000032:analysis; D007545:Isoproterenol / Q000008:administration & dosage / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects* / Q000502:physiology; D009765:Obesity / Q000503:physiopathology*; D010805:Physical Conditioning, Animal / Q000502:physiology; D011817:Rabbits; D012064:Relaxation Therapy; D013997:Time Factors
D000318:Adrenergic beta-Agonists; D006728:Hormones; D007545:Isoproterenol