Flow/shear stress‐induced constriction of rat middle cerebral artery

Abstract

It is known that the intracranial volume is tightly regulated (Monroe‐Kelly doctrine). Thus we hypothesized that increases in flow/wall shear stress elicit constrictions (instead of dilations) in cerebral arteries. Changes of diameter of isolated middle cerebral arteries of rats to increases in intraluminal flow elicited by increasing pressure difference were measured. The diameter of vessels decreased significantly to increases in flow (max.: from 150±10 to 118±6 ηm, from 171±7 to 130±7ηm and from 140±10 to 116±11ηm in the presence of 60, 80, 100 mmHg pressure, respectively, which were inhibited by the non‐specific cyclooxygenase blocker indomethacin. The maximal decrease in diameter to increase in flow at 100 mmHg was 58±4 % of passive diameter obtained in Ca2+ solution. In conclusion, in contrast to responses of coronary and skeletal muscle microvessels, increases in shear stress ‐ via release of constrictor prostaglandins‐ elicit constriction in cerebral arteries, suggesting that the primary purpose of this mechanism is not to maintain wall shear stress, but to limit the increase in blood volume, thus intracranial volume/pressure. (Hungarian Nat. Sci. Res. Fund. ‐ OTKA K71591, K67984, Hungarian Neuroimaging F., NIH‐HL‐43023, AHA Founders Aff., 0555897T)