Purine and pyrimidine metabolism and electrocortical brain activity during hypotension in near-term lambs.

Background: Insufficient cerebral O2 supply leads to cellular energy failure and loss of brain cell function. The relationship between the severity of cellular energy failure due to hemorrhagic hypotension and the loss of electrocortical brain activity (ECBA), as a measure of brain cell function, is not yet fully elucidated in near-term born lambs.

Objectives: To study the relationship between cerebral purine and pyrimidine metabolism, as a measure of brain cell energy failure, and brain cell function after hemorrhagic hypotension in near-term born lambs.

Methods: Eight near-term lambs (term 147 days) were delivered at 131 days of gestation. After a stabilization period, mean arterial blood pressure was reduced till 30% of baseline by withdrawal of blood. Cerebrospinal fluid (CSF) was obtained at the end of the hypotensive period (2.5 h). CSF from 8 siblings was used for comparison. HPLC was used to determine purine and pyrimidine metabolites in CSF, as a measure of cellular energy failure. ECBA was calculated as the root mean square value of a band-filtered (2-16 Hz) one-channel EEG.

Results: Values of guanosine, inosine, hypoxanthine, xanthine and uridine were significantly higher, while ECBA was significantly lower after hemorrhagic hypotension than control values. The concentrations of inosine, hypoxanthine, xanthine and uridine were significantly negatively linearly related to ECBA.

Conclusions: Brain cell function is negatively related to concentrations of inosine, hypoxanthine, xanthine and uridine in the CSF after hemorrhagic hypotension in near-term born lambs.