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1. Cardiac chronotropic responses to isoprenaline are reduced with ageing in man. It is unclear whether this is due to reduced cardiac beta-adrenergic sensitivity or to age-associated differences in reflex cardiovascular responses to the vasodilatory effects of isoprenaline. Age-associated changes in physical activity are also reported to influence beta-adrenergic sensitivity. 2. The aim of the present study was to determine the contribution of alterations in reflex changes in para-sympathetic and sympathetic influences and physical fitness to the age-associated reduction in cardiac chronotropic responses to beta-adrenergic agonists. 3. The effect of 'autonomic blockade' with atropine (40 micrograms/kg intravenously) and clonidine (4 micrograms/kg intravenously) on blood pressure, heart rate and chronotropic responses to intravenous bolus isoprenaline doses was determined in eight healthy young (mean age 21 years), nine healthy elderly (72 years) and 10 endurance-trained elderly (69 years) subjects. 4. Elderly subjects had a reduced increase in heart rate after atropine (young, 49 +/- 9 beats/min; elderly, 36 +/- 5 beats/min; endurance-trained elderly, 34 +/- 12 beats/min; P < 0.01) and did not demonstrate the transient increase in systolic blood pressure after clonidine observed in young subjects (young, 11 +/- 10 mmHg; elderly, -12 +/- 16 mmHg; endurance-trained elderly, -18 +/- 11 mmHg; P < 0.01). 5. Cardiac chronotropic sensitivity to isoprenaline after 'autonomic blockade' increased in the young but decreased in the elderly subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Type

Journal article

Journal

Clin Sci (Lond)

Publication Date

09/1994

Volume

87

Pages

297 - 302

Keywords

Adult, Age Factors, Aged, Aged, 80 and over, Atropine, Autonomic Nervous System, Blood Pressure, Clonidine, Heart, Heart Rate, Hemodynamics, Humans, Isoproterenol, Male, Physical Endurance, Stimulation, Chemical