The response of feline spinal pial arterioles to norepinephrine

Abstract

The effect of norepinephrine on the diameter of feline spinal pial arteries and arterioles was studied by microapplication of the drug to the perivascular environment. Vascular diameter was determined by the television image-splitting method. Application of norepinephrine over the range of 5 .times. 10-8 M to 5 .times. 10-3 M to spinal pial arterioles resulted in constriction of the vessels. The dose-response curve showed a tendency to plateau at concentrations above 5 .times. 10-5 M, with a maximal constriction of 28.8 .+-. 5.1% at 5 .times. 10-3 M. The reduction in vessel diameter to microapplication of norepinephrine was prevented with the inclusion of an equimolar concentration of the .alpha.-adrenergic blocker, phentolamine, in the injectate. The data indicate the presence of .alpha.-adrenergic receptors on the smooth muscle of spinal pial arterioles. The arguments pertaining to the sympathetic control of blood flow in the brain apparently apply also to the spinal cord.