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1 Hypertension Unit, Heart Institute-InCor, Medical School,
3 Conselho Nacional de Desenvolvimento Científico e
Tecnológico Programa Institucional de Bolsas de
Iniciaç
o Científica, 4 Divisão de
Bioengenharia, Heart Institute, Medical School, University of São
Paulo, São Paulo, São Paulo 5403-000; and
2 Laboratory of Cardiovascular Physiology, Department of
Physiology, Basic, and Health Sciences Institute, University of Rio
Grande do Sul, Porto Alegre, Rio Grande do Sul 90050 - 170, Brazil
Aging is associated with altered autonomic control of cardiovascular
function, but baroreflex function in animal models of aging remains
controversial. In this study, pressor and depressor agent-induced
reflex bradycardia and tachycardia were attenuated in conscious old (24 mo) rats [57 and 59% of responses in young (10 wk) Wistar rats,
respectively]. The intrinsic heart rate (HR, 339 ± 5 vs.
410 ± 10 beats/min) was reduced in aged animals, but no
intergroup differences in resting mean arterial blood pressure (MAP,
112 ± 3 vs. 113 ± 5 mmHg) or HR (344 ± 9 vs. 347 ± 9 beats/min) existed between old and young rats, respectively. The
aged group also exhibited a depressed (49%) parasympathetic
contribution to the resting HR value (vagal effect) but preserved
sympathetic function after intravenous methylatropine and propranolol.
An implantable electrode revealed tonic renal sympathetic nerve
activity (RSNA) was similar between groups. However, old rats showed
impaired baroreflex control of HR and RSNA after intravenous
nitroprusside (
0.63 ± 0.18 vs. 1.84 ± 0.4 bars · cycle
1 · mmHg1 · s1).
Therefore, aging in rats is associated with 1) preserved
baseline MAP, HR, and RSNA, 2) impaired baroreflex control
of HR and RSNA, and 3) altered autonomic control of resting HR.
sympathetic activity; cardiovascular function; autonomic control; vagal effect
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