A comparison of the measurements of local cerebral blood flow by hydrogen clearance with hydrogen inhalation and by its electrochemical generation in brain tissue

The goal of the present investigation was to compare data received by modifications of H2-clearance method with inhalation (H2-Inh) and electrochemical generation in brain tissue (H2-Gen) of H2 from the same recording electrodes in acute experiments (urethane 1g/kgip) with Wistar rats (n = 39). Block of three or four Pt electrochemically sharpened electrodes to tip diameters of 20-40 mu, 0.3-0.5 mm apart and 0.8-1.0 mm in length were inserted through the dura into sensorimotor cortex. One electrode was used for H2 generation (DC current 3-5 microA) and the others for PH2 recordings by polarographical method. Durations of H2 inhalation and H2 electrochemical generation were 3 or 10s with similar amplitudes of PH2. Data was recorded with a MacLab analog-digital system and Macintosh 11si computer. Recordings of resting LCBF were made with H2-Gen and H2-Inh the beginning of the experiment and after 40-60 min. LCBF was stimulated with inhalation of 7.5% CO2 for 60s. In 6 preparations LCBF was measured 10-20 min. after occlusions of two branches of the middle cerebral artery. After experiments the brain was perfused with India ink and cut in frozen sections for morphological analyses. The mean values of resting LCBF measured by H2-Inh was 1.67 +/- 0.54 ml/g/min. (+/- SD, N = 149), and by H2-Gen 3.17 +/- 0.91 (N = 147). The diffusional component was estimated as 1.2-2.5 (equivalent units, ml/g/min.) in dead cortex. The ratio of clearances in H2-Gen to H2-Inh varied in different experiments from 1.0 up to 4.0.(ABSTRACT TRUNCATED AT 250 WORDS)