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Summary:We used an isolated, pressurized, and per fused feline middle cerebral artery preparation to mea sure how changes in intraluminal pressure and alterations in O2 and CO2 affect vessel diameter and myogenic con tractile activation before and after treatment with indo methacin (I ND). Vessel diameters were measured over the pressure range 60-140 mm Hg. The arteries were then exposed to low O2 (50 torr) and/or high CO2 (65 torr) and diameters remeasured over the same range. Under con trol conditions, the arteries exhibited myogenic contrac tile activation. Exposure to low O2, high CO2, or a mix ture of low 02/high CO2, increased vessel diameter but did not change the vessels' myogenic contractile respon siveness to changes in pressure. Arteries exposed to IND Arachidonic acid derivatives produced by the ce rebral arteries have many effects on the cerebrovas culature (Pickard and Walker, 1985). Investigations into how these derivatives, particularly prostaglan dins and prostacyclin, affect cerebrovascular regu lation have relied extensively upon the use of the cyclo-oxygenase inhibitor, indomethacin (IND) (Pickard and Walker, 1985). However, many of the findings have been contradictory. In animal studies, results have varied depending upon the species as well as the experimental model used (Leffler et aI., 1985). In some studies IND significantly reduced basal CBF (Pickard and MacKenzie, 1973; McCulReceived October 9, 1991; final revision received March 20, 1992; accepted March 24, 1992. Address correspondence and reprint requests to Dr. Jane A. 866decreased in diameter but retained myogenic contractile activity. In the presence of IND, vessels dilated to both low O2 and a mixture of low 02/high CO2, but did not dilate to high CO2 alone. Under all conditions, vessels retained myogenic contractile activity. Results obtained under control conditions and low O2 confirm those of others using similar systems. Myogenic contractile activ ity in the presence of high CO2 or a mixture of low Ozl high CO2 has not been previously reported. The dilation to low O2 but not to high CO2 in the presence of IND suggests that this drug's effects in cerebral arteries are not limited solely to inhibition of prostaglandin synthesis.

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