The major determinant of vascular resistance is "small arteriolar" (known as resistance arterioles) tone. The endothelium begins to control muscle tone and arteriolar blood flow tissue. The resistance of some sheep to keds was due to prolonged cutaneous arteriolar vasoconstriction. Secondly, a brighter red color spread around the original spot due to arteriolar dilation. Arteriolar vasodilators are substances or medications that preferentially dilate arterioles. Hydralazine can potentially cause this condition as well, as it is a direct arteriolar vasodilator. Cerebral consequences of hypertension&colon; treating high blood pressure prevents only arteriolar strokes. Further local responses to stretch, carbon dioxide, pH, and oxygen also influence arteriolar tone.