Acute hemodynamic responses to intravenous and intra-arterial guanethidine

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Abstract
Intravenous administration of guanethidine to dogs causes an abrupt fall in systemic arterial pressure which is followed by a sustained increase. These studies were made to determine the nature of this biphasic response. Observations were made on dogs before and at frequent intervals after guanethidine was given. A fall in arterial pressure, an increase in cardiac output, and a decrease in peripheral resistance were observed within 10 sec; these changes lasted 40–50 sec. After the depressor phase, blood pressure and stroke volume increased while resistance returned to control levels. These acute changes subsided within 10–15 min. Ganglionic blockade augmented the pressor response and adrenergic blockade reduced it. Intra-arterial injection of guanethidine into perfused denervated forelegs caused brief vasodilatation followed by vasoconstriction. This response was qualitatively different from that seen with intra-arterial injection of norepinephrine. The results support indirectly the hypothesis that the systemic pressor response is caused by circulating catecholamines. The results demonstrate also that the drug has a local vasodilator action on the blood vessels of the foreleg.