Alpha Receptor Stimulation by Norepinephrine and Blockade by Benoxathian in spinal Pial Arteries of Rabbit

ABSTRACT

The effect of norepinephrine and benoxathian 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. Physiological parameters(PaO2, PaCO2, blood pH, and systolic blood pressure) were not significantly changed during all experiments. The results of this study are summerized as follow. 1) Application of norepinephrine over the range of 5x10(-8)M to 5x10(-3)M to spinal pial arteries resulted in significant constriction which were shown to be proportional to concentration, with exception of 5x10(-8)M. The dose response curve showed constriction of 30.5+/-7.1% at 5x10(-3)M. 2) Benoxathian produced the vasodilatation which were shown to be proportional to concentration. The dose response curve showed vasodilatation of 21.4+/-4.4% at 5x10(-3)M 3) The vasoconstriction due to microapplication of norepinephrine was prevented by the inclusion of an equimolar concentration of the alpha-adrenergic receptor blocker, benoxathian. 4) The vasoconstriction due to norepinephrine was present in the concentration of norepinephrine more than that of benoxathian, and the vasoconstriction was proportional to the concentration of norepinephrine. The results indicate that alpha-adrenergic receptor is present in the smooth muscle of spinal pial arteries for the sympathetic control of blood flow to the spinal cord.