The Effect of Topical Application of norepinephrine and Phentolamine on Spinal Pial Arteries in Rabbit

ABSTRACT

The effect of norepinephrine and phentolamine on the diameter of spinal pial arteries in rabbits was studied by topical microapplication of the drug to the perivascular environment. Arterial diameter was determined with the micrometer eyepiece on operating microscope through laminectomized area. Changes of physiological parameters(PaO2, PaCO2, blood pH, and systolic blood pressure) were not significant during all of the experiments. 1) Application of nerepinephrine over the range of 5x10(-8)M to 5x10(-3)M to the spinal pial arteries resulted in significant constriction of the vessels, with the exception of 5x10(-8)M. The dose-response curve showed a maximal constriction 30.5+/-7.1% at 5x10(-3)M. 2) Phentolamine produced no significant vasodilatation. 3) The vasoconstriction due to microapplication of norepinephrine was prevented by the inclusion of an equimolar concentration of the alpha-adrenergic blocker, phentolamine. 4) The vasoconstriction due to norepinephrine was evident while the concentration of norepinephrine was more than that of phentolamine. Furthermore the degree of vasoconstriction was proportional to the concentration of norepinephrine. The results indicate that alpha-adrenergic receptors are present in the smooth muscle of spinal pial arteries for the sympathetic control of blood flow to the spinal cord.