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  • Title: Direct effects of alpha1- and alpha2-adrenergic agonists on spinal and cerebral pial vessels in dogs.
    Author: Iida H, Ohata H, Iida M, Watanabe Y, Dohi S.
    Journal: Anesthesiology; 1999 Aug; 91(2):479-85. PubMed ID: 10443612.
    Abstract:
    BACKGROUND: The effects of adrenergic agonists, often used as local anesthetic additives or spinal analgesics, on spinal vessels have not been firmly established. The authors investigated the effects of alpha2- and alpha1-adrenergic agonists on spinal and cerebral pial vessels in vivo. METHODS: Pentobarbital-anesthetized dogs (n = 28) were prepared for measurement of spinal pial-vessel diameter in a spinal-window preparation. The authors applied dexmedetomidine, clonidine, phenylephrine, or epinephrine in three different concentrations (0.5, 5.0, and 50 microg/ml; [2.1, 1.9, 2.5, and 2.3] x [10(-6), 10(-5), and 10(-4)] M, respectively) under the window (one drug in each dog) and measured spinal pial arteriolar and venular diameters in a sequential manner. To enable the comparison of their effects on cerebral vessels, the authors also administered these drugs under a cranial window. RESULTS: On topical administration, each drug constricted spinal pial arterioles in a concentration-dependent manner. Phenylephrine and epinephrine induced a significantly larger arteriolar constriction than dexmedetomidine or clonidine at 5 microg/ml (8%, 11%, 0%, and 1%, respectively). Spinal pial venules tended to be less constricted than arterioles. In cerebral arterioles, greater constrictions were induced by dexmedetomidine and clonidine than those induced by phenylephrine and epinephrine (14%, 8%, 0%, and 1%, respectively). Cerebral pial venules tended to exhibit larger constrictions than cerebral arterioles (unlike in spinal vessels). CONCLUSION: Dexmedetomidine and clonidine constricted spinal vessels in a concentration-dependent manner, but such vasoconstrictions were smaller than those induced by phenylephrine and epinephrine.
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