NOS inhibitors decrease hypoxia-induced ATP reductions in respiring cerebrocortical slices

Background: Excess neuronal nitric oxide (NO) production might cause adenos ine triphosphate loss and cellular damage in hypoxic brain parenchyma, (31) p nuclear magnetic resonance spectroscopy was used to study hypoxic intrace llular responses in perfused respiring cerebrocortical slices, in which NO scavenging by hemoglobin is absent, during NO synthase blockade and NO augm entation. Methods: Adenosine triphosphate concentrations were monitored at 4.7 Tesla in respiring slices before, during, and after 60 min of hypoxia (oxygen ten sion < 5 mmHg), Slices were not treated or were pretreated with 27 mu M L-n itroarginine methyl ester (L-NAME), 27 mu M 7-nitroindozole (7-NI), or 27 m u M L-nitroarginine. Nitrotyrosine:tyrosine ratios of slice extracts were m easured using high-performance liquid chromatography. Cresyl violet-stained sections (2 mu m) from random slices n ere examined histologically. Results: After 60 min of hypoxia, adenosine triphosphate decreased to less than or equal to 3, less than or equal to 3, 65 +/- 6, and 25 +/- 4% of con trol in slices that were untreated or treated with L-nitroarginine, L-NAME, and 7-NI, respectively. After 120 min of hyperoxic recovery, adenosine tri phosphate levels returned to control values in slices pretreated with L-NAM E and 7-NI, but to only 30% of control in untreated or nitroarginine-treate d slices, Nitric oxide donors administered during posthypoxic recovery part ially antagonized the adenosine triphosphate recovery found with L-NAME and 7-NI, Nitric oxide synthase activity in slice homogenates, assayed via con version of L-arginine to citrulline, was less than or equal to 2% of contro l after all inhibitory treatments. The nitro-tyrosine:tyrosine ratio increa sed by 52% in slices treated with 7-NI and by 200-300% in all other groups. Pretreatment with L-NAME and 7-NI reduced histologic evidence of cell swel ling. Conclusion: Neuronal NO is associated with rapid adenosine triphosphate red uctions and peroxynitrite formation in acutely hypoxic cerebrocortical slic es.