title: Loss of resting bradycardia with detraining is associated with intrinsic heart rate changes.
abstract: The mechanisms underlying the loss of resting bradycardia with detraining were studied in rats. The relative contribution of autonomic and non-autonomic mechanisms was studied in 26 male Wistar rats (180-220 g) randomly assigned to four groups: sedentary (S, N = 6), trained (T, N = 8), detrained for 1 week (D1, N = 6), and detrained for 2 weeks (D2, N = 6). T, D1 and D2 were treadmill trained 5 days/week for 60 min with a gradual increase towards 50% peak VO2. After the last training session, D1 and D2 were detrained for 1 and 2 weeks, respectively. The effect of the autonomic nervous system in causing training-induced resting bradycardia and in restoring heart rate (HR) to pre-exercise training level (PET) with detraining was examined indirectly after cardiac muscarinic and adrenergic receptor blockade. T rats significantly increased peak VO2 by 15 or 23.5% when compared to PET and S rats, respectively. Detraining reduced peak VO2 in both D1 and D2 rats by 22% compared to T rats, indicating loss of aerobic capacity. Resting HR was significantly lower in T and D1 rats than in S rats (313 +/- 6.67 and 321 +/- 6.01 vs 342 +/- 12.2 bpm) and was associated with a significantly decreased intrinsic HR (368 +/- 6.1 and 362 +/- 7.3 vs 390 +/- 8 bpm). Two weeks of detraining reversed the resting HR near PET (335 +/- 6.01 bpm) due to an increased intrinsic HR in D2 rats compared with T and D1 rats (376 +/- 8.8 bpm). The present study provides the first evidence of intrinsic HR-mediated loss of resting bradycardia with detraining in rats.
authors: Departamento de Biodinâmica do Movimento do Corpo Humano, Escola de Educação Física e Esporte, Universidade de São Paulo, SP, Brasil.
authors: F S
authors: FS
authors: Evangelista
authors: S E D
authors: SE
authors: Martuchi
authors: C E
authors: CE
authors: Negrão
authors: P C
authors: PC
authors: Brum
mesh_terms: D000818:Animals; D001341:Autonomic Nervous System / Q000502:physiology*; D001919:Bradycardia / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology*; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D012146:Rest / Q000502:physiology*