Direct effects of alpha1- and alpha2-adrenergic agonists on spinal and cerebral pial vessels in dogs.
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).


CONCLUSIONS
Dexmedetomidine and clonidine constricted spinal vessels in a concentration-dependent manner, but such vasoconstrictions were smaller than those induced by phenylephrine and epinephrine.
Iida
H
H
Department of Anesthesiology and Critical Care Medicine, Gifu University School of Medicine, Gifu City, Japan. iida@cc.gifu-u.ac.jp
Ohata
H
H
Iida
M
M
Watanabe
Y
Y
Dohi
S
S
D058646:Adrenergic alpha-1 Receptor Agonists; D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001160:Arterioles / Q000187:drug effects; D001921:Brain / Q000098:blood supply*; D002560:Cerebrovascular Circulation / Q000187:drug effects; D003000:Clonidine / Q000494:pharmacology; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D020926:Medetomidine; D010656:Phenylephrine / Q000494:pharmacology; D013116:Spinal Cord / Q000098:blood supply*; D014661:Vasoconstriction / Q000187:drug effects*
D058646:Adrenergic alpha-1 Receptor Agonists; D058647:Adrenergic alpha-2 Receptor Agonists; D000316:Adrenergic alpha-Agonists; D007093:Imidazoles; D010656:Phenylephrine; D003000:Clonidine; D020926:Medetomidine; D004837:Epinephrine