EFFECT OF PERINATAL ASPHYXIA ON SYSTEMIC AND INTRACEREBRAL PH AND GLYCOLYSIS METABOLISM IN THE RAT

The effects of perinatal asphyxia on systemic and brain pH and glycoly sis metabolism were studied in the rat. Perinatal asphyxia was induced by immersing pup-containing uterus horns, obtained by cesarean sectio n from rats within the last day of gestation, in a water bath at 37 de grees C for various periods of time (0-23 min). Subcutaneous levels of pyruvate (Pyr), lactate (Lact), glutamate (Glu), and aspartate (Asp) were monitored with microdialysis 40-80 min after delivery. In paralle l experiments, the pups were sacrificed 40 min after delivery and the heart and brain were removed for measuring pH. Brain (striatum) Pyr, L act, Glu, and Asp levels were also analyzed. A decrease in the rate of survival was first observed following asphyctic periods longer than 1 6 min, and no survival could be observed after 22 min of asphyxia. In control (cesarean-delivered) pups, heart and brain pH were 7.36 +/- 0. 01 (N = 8) and 7.30 +/- 0.01 (N = 8), respectively. Significant decrea ses in pH were first observed following 5-6 and 10-11 min of asphyxia, in heart and brain, respectively. In both regions pH decreased along with the length of asphyxia, but a decrease below 7 was only observed in the brain, following asphyctic periods longer than 16 min. A signif icant increase in subcutaneous Lact levels was first observed followin g 2-3 min of asphyxia, with a maximum after 20-21 min of asphyxia. In the brain, the increase in Lact levels was delayed compared to that ob served in subcutaneous tissue. Pyr and Asp levels increased in subcuta neous tissue following perinatal asphyxia and decreased in brain tissu e following > 15 min of asphyxia. Glu levels were increased subcutaneo usly by moderate (5-16 min) asphyctic periods, but, in the brain, were only transiently increased by 10-11 min of asphyxia. Thus, changes in systemic pH, glycolysis, and excitatory amino acid metabolism are obs erved following shorter asphyctic periods than are changes in the brai n. In particular, increases in subcutaneous Lact levels precede: (i) a decrease in brain pH, (ii) an increase in brain Lact levels, (iii) a decrease in the rate of survival, and, probably, (iv) brain damage. It is suggested that monitoring Lact levels by subcutaneous microdialysi s is a useful method for predicting the outcome produced by hypoxic-is chemic insults. (C) 1997 Academic Press.