Comparison of the myogemc response in rat cerebral arteries of different calibers

The myogenic response was studied in rat cerebral arteries of different calibers. Middle cerebral arteries (MCAs), 2nd and 3rd order branches of the MCA, and penetrating arterioles were isolated from male rats and pressurized. The vessels were initially pressurized to 50 mm Hg for 1 hour. Subsequently, changes in diameter were measured as the transmural pressure was changed between 20 and 100 mm Hg. During the 1 hour stabilization period, the MCA demonstrated the greatest development of spontaneous tone of the vessels studied, constricting by 22 ± 6% (n=9). The MCA branches and arterioles constricted by 12 ± 4% (n=8) and 14 ± 4% (n=8), respectively. After the development of spontaneous tone (50 mm Hg), the mean inner diameter of rat MCAs was 202 ± 10 μm (n=9), branches 118 ± 14 μm (n=8) and penetrating arterioles 58 ± 4 μm (n=8). The MCAs showed little or no myogenic response between 20 and 40 mm Hg, a slight myogenic response between 40 and 60 mm Hg, and a pronounced myogenic response between 60 and 100 mm Hg (8% constriction, p<0.01). The penetrating arterioles showed the greatest myogenic response between 20 and 40 mm Hg (8% constriction, p<0.01) with a diminished myogenic response between 60 and 100 mm Hg. Branches of the MCA showed a myogenic response over the entire pressure range (8% constriction over 20 to 100 mm Hg, p<0.01). The results of the present study demonstrate the correlation of vessel caliber on responses to changes in transluminal pressure. This suggests that the myogenic response for cerebral vessels of smaller caliber occurs at a lower pressure. It is suggested that the different mechanical characteristics of the cerebral arterioles compared with that of the MCA and branches may facilitate their role in controlling cerebrovascular resistance.