Autonomic mechanisms of training bradycardia: beta-adrenergic receptors in humans

Five healthy adult well trained men (averaging 49 miles running per week) were exercised to exhaustion on a treadmill. Plasma epinephrine increased from 168 \m=+-\37 pg/ml prior to exercise to 633 \ m=+-\155 pg/ml immediately after exercise (P < 0.025) and plasma norepinephrine increased from 1608 \ m=+-\345 to 8576 \m=+-\1662 pg/ml (P < 0.025) in the two respective periods. Beta receptor density increased from 53 \ m=+-\18 fmol/mg protein before exercise, to 223 \m=+-\63 fmol/mg (P < 0.05) protein immediately after exercise, and then decreased to 83 \ m=+-\ 27 fmol/mg protein 1 h later (P < 0.05 compared to postexercise). The mean Kd value prior to exercise of 1.5 \ m=+-\ 0.2 \ m=x\10\m=-\11 m was unchanged statistically throughout the study. Following correction for haemodilution, serum total and free T4 and T3 concentrations were also unchanged during exercise, although reverse T3 levels did increase from 39 \ m=+-\ 4 to 45 \ m=+-\ 0 ng/dl (P < 0.05). These findings suggest that: 1) plasma epinephrine, norepinephrine and beta receptor density, but not Kd, increase acutely during exercise and 2) total and free T4 and 3, after correction for haemodilution, do not change during acute exercise.Our data indicate that acute exercise represents an unusual condition during which 'down regulation' is not observed, but, rather, there appear to be parallel altera¬ tions in beta receptor density and plasma catecholamine levels.Recent studies by Tohmeh & Cryer (1980) have demonstrated the unexpected finding that isopro¬ terenol infusion initially (up to 1 h) increased beta receptor density in peripheral mononuclear cells whereas continuation of the infusion for 4-6 h gradually decreased beta receptor density; epine¬ phrine infusion (0-1 h) also increased beta re¬ ceptor density. These findings were unexpected since earlier work had demonstrated that chroni¬ cally increased catecholamine levels caused a 'down regulation' and resultant decrease in beta receptor number (Lefkowitz 1979;Motulsky & Insel 1982).These trends in beta receptor numbers appear dependent upon the time period of the elevated plasma catecholamines and these studies stimu¬ lated interesting questions concerning the mecha¬ nism by which such an early rapid increase in beta receptor density could occur, especially consider¬ ing the unlikely possibility that this increase repre¬ sents new receptor synthesis. We decided to inve¬ stigate whether endogenous elevations in plasma catecholamines would also be associated with shortterm increases in beta receptor density.

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“…These parameters were also not changed in longitudinal studies as normal volunteers exercised (Williams et al 1981). …”

Section: Discussionmentioning

confidence: 90%

Beta receptors in peripheral mononuclear cells increase acutely during exercise

Burman

Ferguson

Djuh

et al. 1985

Acta Endocrinologica

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“…However, several other studies have failed to demonstrate differences in vagal tone between trained and untrained subjects (6,32,36,37). Yet, others have indicated a decrease in sympathetic activity in the sinus node (38) or both an increase in vagal activity and a decrease in sympathetic activity (39). On the other hand, studies on animals (33) and on humans (6,32,36,40) have suggested that this bradycardia is mainly due to a reduction in intrinsic HR.…”

Section: Discussionmentioning

confidence: 99%

Effects of aerobic exercise training on heart rate variability during wakefulness and sleep and cardiorespiratory responses of young and middle-aged healthy men

Catai

Chacon-Mikahil

Martinelli

et al. 2002

Braz J Med Biol Res

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The purpose of the present study was to evaluate the effects of aerobic physical training (APT) on heart rate variability (HRV) and cardiorespiratory responses at peak condition and ventilatory anaerobic threshold. Ten young (Y: median = 21 years) and seven middle-aged (MA = 53 years) healthy sedentary men were studied. Dynamic exercise tests were performed on a cycloergometer using a continuous ramp protocol (12 to 20 W/min) until exhaustion. A dynamic 24-h electrocardiogram was analyzed by time (TD) (standard deviation of mean R-R intervals) and frequency domain (FD) methods. The power spectral components were expressed as absolute (a) and normalized units (nu) at low (LF) and high (HF) frequencies and as the LF/HF ratio. Control (C) condition: HRV in TD (Y: 108, MA: 96 ms; P<0.05) and FD -LFa, HFa -was significantly higher in young (1030; 2589 ms 2 /Hz) than in middle-aged men (357; 342 ms 2 /Hz) only during sleep (P<0.05); posttraining effects: resting bradycardia (P<0.05) in the awake condition in both groups; V . O 2 increased for both groups at anaerobic threshold (P<0.05), and at peak condition only in young men; HRV in TD and FD (a and nu) was not significantly changed by training in either groups. The vagal predominance during sleep is reduced with aging. The resting bradycardia induced by short-term APT in both age groups suggests that this adaptation is much more related to intrinsic alterations in sinus node than in efferent vagal-sympathetic modulation. Furthermore, the greater alterations in V . O 2 than in HRV may be related to short-term APT.

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“…The remaining relations between aging and the other variables of Figures 1 and 2 were described earlier. 8 Although increased physiological sensitivity to catecholamines results from aerobic training, details of this adaptation are not completely clear; that is, whereas R. S. Williams, Eden, Moll, Lester, and Wallace (1981) found increased beta-receptor sensitivity in only skeletal (not heart) muscle after aerobic training in human subjects and R. S. Williams, Caron, and Daniel (1984) found similar results in rats, others have found heart sensitivity increases. Even sympathetic nervous system nerve fi ber densities have been increased in the hearts of rats trained by running throughout their adult lives, in comparison with untrained rats (Alho, Koistinaho, Kovanen, Suominen, & Hervonen, 1984).…”

Section: Research Confi Rmation Of the Modelmentioning

confidence: 99%

Arousal and physiological toughness: Implications for mental and physical health.

Dienstbier

1989

Psychological Review

796

585

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From W. B. Cannon's identification of adrenaline with "ftght or flight" to modern views of stress, negative views of peripheral physiological arousal predominate. Sympathetic nervous system (SNS) arousal is associated with anxiety, neuroticism, the Type A personality, cardiovascular disease, and immune system suppression; illness susceptibility is associated with life events requiring adjustments. "Stress control" has become almost synonymous with arousal reduction. A contrary positive view of peripheral arousal follows from studies of subjects exposed to intermittent stressors. Such exposure leads to low SNS arousal base rates, but to strong and responsive challenge-or stressinduced SNS-adrenal-medullary arousal, with resistance to brain catecholamine depletion and with suppression of pituitary adrenal-cortical responses. That pattern of arousal defines physiological toughness and, in interaction with psychological coping, corresponds with positive performance in even complex tasks, with emotional stability, and with immune system enhancement. The toughness concept suggests an opposition between effective short-and long-term coping, with implications for effective therapies and stress-inoculating life-styles.Confrontations with stressors and challenges evoke central and peripheral physiological arousal. Characterizations of that peripheral arousal traditionally have been negative, but some modern views are more positive. After providing some definitions, I discuss the apparent contradictions between literatures whose basis is an assumption of the harmfulness of peripheral physiological arousal and those whose basis is not. DefinitionsAccording to Folkman and Lazarus (1985), the term stress implies "a relationship between the person and the environment that is appraised by the person as relevant to his or her well-being and in which the person's resources are taxed or exceeded" (p. 152). As components of stress, Folkman and Lazarus described threat as "potential for harm or loss," challenge as "potential for growth," and harm-loss as "injury already done" (p. 152). However, because I often emphasize the differences between challenge, on the one hand, and threat and loss, on the other, I use the term challenge separately, using stress to capture only the components of the concept associated with threat and harm/loss.

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Autonomic mechanisms of training bradycardia: beta-adrenergic receptors in humans

Cited by 55 publications

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Beta receptors in peripheral mononuclear cells increase acutely during exercise

Beta receptors in peripheral mononuclear cells increase acutely during exercise

Effects of aerobic exercise training on heart rate variability during wakefulness and sleep and cardiorespiratory responses of young and middle-aged healthy men

Arousal and physiological toughness: Implications for mental and physical health.

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