Journals of Gerontology Series A: Biological Sciences and Medical Sciences Large Type Edition
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Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 52, Issue 1 M36-M43, Copyright © 1997 by The Gerontological Society of America

JOURNAL ARTICLE

Dopaminergic responses in the Fischer 344 rat heart: preserved chronotropic and dromotropic responses with aging

JB Schwartz
Department of Medicine, Northwestern University Medical School, Chicago, USA. [email protected]

BACKGROUND: Marked decreases in cardiac responses to beta-adrenergic stimuli have been found in cellular, animal, and human models of physiologic aging. As another probe of receptor-regulated cardiovascular changes with aging, responses to dopamine were studied. Responses were studied with and without depletion of myocardial catecholamines to eliminate effects secondary to myocardial catecholamine release. METHODS: Responses of heart rate (A-A intervals), atrioventricular conduction (AV intervals and AV Wenckebach block cycle length) to 0-50 microM dopamine were studied in Langendorff perfused hearts from 10 mature (6.2 +/- 0.8 mo, mean +/- SD) and 9 senescent (23.6 +/- 0.7 mo) Fischer 344 rats and in hearts from 10 mature (5.3 +/- 0.4 mo) and 8 senescent (23.9 +/- 0.8) Fischer 344 rats after myocardial catecholamine depletion by reserpine (0.25 mg/kg i.p. x 5 days). RESULTS: Dopamine decreased A-A (p < .0001) and AV conduction intervals (p < .0001) and increased peak developed pressure (p < .0001) and dP/dt (p < .001) in hearts from nonreserpine treated mature and senescent rats. Greater decreases in A-A intervals and AV conduction were seen in senescent compared to mature hearts (p < .0001). Contractile responses were greater in mature hearts (p < .001). After reserpine, A-A interval and paced AV conduction dose vs response relationships shifted rightward (p < .0001), but peak responses and age- related differences in responses were not significantly affected. In contrast, increases in peak developed pressure were greatly reduced in mature hearts (p < .0001) and age-related differences in contractile responses to dopamine were eliminated in hearts from reserpine-treated rats. CONCLUSIONS: (a) A-A interval and AV conduction responses to dopamine were greater in senescent hearts even after catecholamine depletion, suggesting age-related differences in sinus and AV nodal responses to direct dopaminergic stimuli exist. (b) Age-related differences in contractile responses to dopamine were eliminated by reserpine suggesting basal age-related differences in response were secondary to age-related differences in responses to myocardial catecholamine release.




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