Effects of Diltiazem on Myogenic Tone in Pressurized Brain Arteries from Spontaneously Hypertensive Rats

Abstract

The inhibitory effects of diltiazem on myogenic tone in resistance-sized branches of the posterior cerebral artery from 16- to 24-week-old hypertensive (SHRSP) and normotensive (WKY) rats were studied. Using a video-electronic technique, which permits measurement of the lumen diameter and wall thickness, freshly excised arteries were mounted on a microcannula and pressurized to 75 mmHg. During equilibration, or shortly thereafter, spontaneous tone developed, resulting in a 35% reduction of lumen diameter (180–118 μm, ID). When diltiazem was added cumulatively in concentrations from 10-8 to 10-5 M, progressive relaxation was observed. The calculated IC50 values, 7.7 × 10-7 M (SHRSP) and 8.9 × 10-7 M (WKY), were not significantly different. Arteries from hypertensive animals showed rhythmic diameter oscillations which were also suppressed by diltiazem. These results show that: (1) the level of spontaneous tone is similar in resistance-sized cerebral arteries taken from hypertensive and normotensive rats; (2) tone is dependent on the influx of extracellular calcium; and (3) the diltiazem sensitivity of the population of calcium channels responsible for maintaining this tone is not altered in this genetic model of hypertension.