Differential Effects of Dihydroergotamine on the Circulatory Actions of Arterial and Venous Dilators in the Rat

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Abstract
Summary We attempted to characterize six vasodilators with respect to their arterial or venous activity by studying their interaction with the circulatory effects of dihydroergotamine (DHE) in pentobarbital-anesthetized rats. DHE is a selective venoconstrictive agent which increases mean arterial pressure (MAP) and cardiac output (CO) in the pithed rat without affecting peripheral resistance (R). In the anesthetized rat no effect of DHE on MAP, CO, and R could be demonstrated. In the anesthetized rat the hypotensive effect of venodilators (sodium nitrite, glyceryl trinitrate, and molsidomine) was diminished after pretreatment with DHE, whereas the decrease in MAP induced by arterial vasodilators (hydralazine, diazoxide, and endralazine) remained unaltered after pretreatment with DHE. After pretreatment with DHE, the decrease in CO by sodium nitrite was diminished, whereas its effect on R was not altered. The response of CO and R to hydralazine was not altered after pretreatment with DHE. Pretreatment with DHE offers the possibility of differentiating between arterial or venous activity of vasodilators in vivo.

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