CORRELATION OF RAPID CHANGES IN THE AVERAGE WATER DIFFUSION CONSTANT AND THE CONCENTRATIONS OF LACTATE AND ATP BREAKDOWN PRODUCTS DURING GLOBAL-ISCHEMIA IN CAT BRAIN

Rapid changes in the average water diffusion constant, D-av = 1/3{D-xx + D-yy + D-zz}, and in the concentrations of lactate and purine nucle otides and nucleosides were measured upon global ischemia (cardiac arr est) in cat brain, at a combined time resolution of 36 s (n = 7). At t his time resolution, the normalized time curves of 1 - D-av and the in creases in ATP breakdown products did not coincide, with the changes i n D-av being most rapid. The normalized curves of 1 - D-av and the lac tate increase coincided for the first 2-2.5 min after which the change in D-av was more rapid. After this time point, an excellent correlati on was found between the drop in D-av and the decrease in energy utili zation rate, which was calculated from the measured time curves of lac tate formation and ATP breakdown, and from the time curve for phosphoc reatine use reported in the literature, These results are in agreement with the expected biphasic changes in ion and water homeostasis durin g ischemia and with the model of diffusional changes being a consequen ce of a water shift from interstitial to intracellular space.