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- May 13, 2014
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I read from UWorld that alpha1 agonist such as phenylephrine (a1>a2) decreases CO because of the combined effects of increased sympathetic tone (vasoconstriction) from alpha2 and vascoconstriction from alpha1. The answer also stated that the agonist would also decrease preload or venous return.
1. But wouldn't sympathetic activation from alpha1 receptor elevate HR, and thus would compensate for the increased TPR, and maintain constant CO?
2. I think I read from other sources that alpha1 agonist activity includes increasing venous tone (venoconstriction). Shouldn't the drug then increas the venous return?
3. What's the alpha2's effect on venous tone?
I'd appreciate any help!
1. But wouldn't sympathetic activation from alpha1 receptor elevate HR, and thus would compensate for the increased TPR, and maintain constant CO?
2. I think I read from other sources that alpha1 agonist activity includes increasing venous tone (venoconstriction). Shouldn't the drug then increas the venous return?
3. What's the alpha2's effect on venous tone?
I'd appreciate any help!