Key result
In conscious dogs, vasopressin, but not sympatholytics or angiotensin, markedly attenuated the increased cardiac output and tachycardia associated with minoxidil or hydralazine administration.
Why the study?
How do sympatholytics, angiotensin, and vasopressin affect the cardiovascular response to minoxidil or hydralazine in conscious dogs?
How do sympatholytics, angiotensin, and vasopressin affect the cardiovascular response to minoxidil or hydralazine in conscious dogs?
In conscious dogs, vasopressin acts as a functional antagonist to the increased cardiac output and tachycardia induced by minoxidil or hydralazine, suggesting these responses are not dependent on sympathetic reflexes or cardiac afterload.
Vasopressin attenuates vasodilator-induced hemodynamics in dogs; leaves open relevance to human therapy.
Oral administration of minoxidil, 1 mg/kg, or hydralazine, 12 mg/kg, decreased arterial blood pressure and peripheral vascular resistance, while cardiac output and rate increased in conscious dogs. These responses were not significantly altered by treatment with propranolol or phenoxybenzamine. Angiotensin infusions sufficient to increase arterial blood pressure to levels observed before treatment with the vasodilators did not obtund the heightened cardiac activity. In contrast, vasopressin infusions sufficient to normalize blood pressure markedly attenuated the increased cardiac output and rate associated with minoxidil or bydralazine. The results suggest that the increased cardiac output and tachycardia associated with administration of minoxidil or hydralazine are not dependent upon sympathetic nervous reflexes or cardiac afterload. The compensatory bradycardia normally associated with blood pressure increases appeared to be inhibited in the presence of minoxidil or hydralazine. In these experiments, vasopressin was a functional antagonist to the cardiovascular response associated with the administration of minoxidil or hydralazine.
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Wendling et al. (1979) studied this question. Minoxidil or hydralazine was evaluated on Cardiovascular response (arterial blood pressure, peripheral vascular resistance, cardiac output, and rate). In conscious dogs, vasopressin, but not sympatholytics or angiotensin, markedly attenuated the increased cardiac output and tachycardia associated with minoxidil or hydralazine administration.
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