The aim of this study was to estimate the effect of Nitric Oxide synthase (NOS)-inhibition (L-NMMA) on the diameter of the middle cerebral artery (MCA) and on regional cerebral blood flow (rCBF). Furthermore, to assess the effect of L-NMMA on acetazolamide induced increases in MCA blood velocity (Vmean) and rCBF. In an open crossover design 12 healthy subjects attended the laboratory twice. The first day 6 mg/kg L-LNMMA i.v. over 15 min preceded 1 g acetazolamide iv over 5 min. Eight days later only acetazolamide was given. Vmean in MCA was determined with transcranial Doppler (TCD) and rCBF with Xe-133 inhalation SPECT at baseline, after L-NMMA and 25 and 55 min after acetazolamide infusion. After L-NMMA the decrease in rCBFMCA was 6.8% (± 7.4) ( P < 0.019, n = 12), whereas Vmean was not affected ( P = 0.83, n = 8). The change in MCA diameter was estimated to -1.3% ( P = 0.44, n = 8). L-NMMA did not affect acetazolamide increases in Vmean ( P = 0.67, n = 8) nor rCBF ( P = 0.29, n = 12). The percentage increase of Vmean was 1.5 times that of rCBF ( n = 8). Our data suggest that the basal tone of human cerebral arterioles but not of conduit arteries is NO-dependent. The action of acetazolamide in man is not NO-dependent.
Effects of route of administration on oxytocin-induced changes in regional cerebral blood flow in humans
