A study of rat intracerebral arterioles: methods, morphology, and reactivity.

Penetrating, intracerebral arterioles from rat were isolated, cannulated, and studied in vitro. Vessel wall elements were found to consist of an endothelial cell layer, one smooth muscle cell layer, and a thin adventitial layer or leptomeningeal sheath. Smooth muscle cell nuclei were oriented perpendicular to the vessel's longitudinal axis; endothelial cell nuclei were parallel to the axis. Mean vessel diameter with the smooth muscle inactivated (passive diameter) was 36.7 +/- 1.6 (SE) micrometer. Spontaneous smooth muscle tone developed at 37 degrees C and reduced vessel diameter to 70 +/- 4% of passive diameter. Vessels were activated by the extraluminal application of 140 mM KCl solution at pH 8.00, which produced a transient contraction that decayed within 30 s to a steady contraction of somewhat less intensity. Changes in intravascular pressure were used to alter wall tension of the vessels. Tension in the vessel wall was computed, and length-tension curves for the arteriolar smooth muscle were approximated. Length-tension relationships similar to those seen in other smooth-muscle preparations were found with maximal estimated force development of 1.29 x 10(-5) N . m-2. Alterations of bath pH caused changes in vessel diameter that were inversely related to extraluminal pH and varied by approximately 77% in the range from pH 6.85 to 8.00. Adenosine dilated vessels to 140 +/- 6% of control diameter at a concentration of 10(-5) M. The mechanical characteristics and the reactivity to H+, K+, and adenosine of these vessels were quantitatively consistent with in vitro data from larger cerebral vessels and in vivo data from pial arteries.