Cardiovascular and plasma catecholamine response to static exercise in normotensive blacks and whites

OBJECTIVES: The objectives of the present study were (1) to evaluate the pressor response to an isometric handgrip exercise in normotensive black and white males; (2) to measure plasma catecholamine levels pre- and post-exercise, as an index of sympathetic nervous system activity; and (3) to quantify the pressor response to bolus intravenous injections of phenylephrine (an alpha-specific agonist). METHODS: Cardiovascular and catecholamine responses to an isometric handgrip exercise (3 minutes at 30% MVC) were measured in 15 normotensive blacks and whites. In another phase of the study, pressor responses to bolus injections of phenylephrine were assessed to evaluate alpha-adrenergic sensitivity. RESULTS: The blood pressure in the blacks increased from 119/69 to 160/120 mm HG during isometric exercise, while in the whites it increased from 118/67 to 153/110 mm HG. The blacks exhibited a greater diastolic blood pressure reactivity, as evidenced by a significant race x time interaction (p < 0.05). The heart rate responses were not significantly different between the two groups. The plasma levels of norepinephrine were similar at rest, but were 25% lower in the blacks than in the whites following isometric exercise (p < 0.01). Black subjects also demonstrated an increased pressor response to intravenous injections of phenylephrine at rest (p < 0.05). CONCLUSIONS: The enhanced vascular sensitivity to norepinephrine may have contributed to the greater exercise pressor response in the blacks.