Neurogenic and Chemical Influences on the Diameter of Pial Veins

Summary

Neurogenic and chemical influences on the diameter of the pial vessels were assessed in 16 cats using a microphotographic technique. Hypotension, induced by exsanguination, resulted in a marked autoregulatory dilatation of the larger arteries, but the changes in the veins and the smaller arteries were less marked. Hypertension, induced by reinfusion of the blood, resulted in a marked autoregulatory constriction of the larger arteries, but the changes in the veins and the smaller arteries were less. Hexamethonium (5 mg/kg i.v.) caused minimal changes in the vessel diameters. 5-Hydroxydopamine (5 mg/kg i.v.) resulted in a significant dilatation of the arteries and the smaller veins, but did not dilate the larger veins. Papaverine (5 mg/kg i.v.) had effects on the pial vessels similar to those of 5-hydroxydopamine. Inhalation of 5% CO₂ caused a marked dilatation of the smaller veins and arteries, but did not show significant effects on the larger vessels. Hyperventilation resulted in a significant constriction of the small veins and arteries, but did not cause a significant change in the diameters of the larger vessels.

These data suggest that the diameter of the pial veins was influenced both neurogenically and chemically, but also that the effects of these two agents were less marked in the veins than in the arteries.