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

Excess neuronal nitric oxide (NO) production might cause adenosine triphosphate loss and cellular damage in hypoxic brain parenchyma. 31P nuclear magnetic resonance spectroscopy was used to study hypoxic intracellular responses in perfused respiring cerebrocortical slices, in which NO scavenging by hemoglobin is absent, during NO synthase blockade and NO augmentation.

Adenosine triphosphate concentrations were monitored at 4.7 Tesla in respiring slices before, during, and after 60 min of hypoxia (oxygen tension < 5 mmHg). Slices were not treated or were pretreated with 27 microM L-nitroarginine methyl ester (L-NAME), 27 microM 7-nitroindozole (7-NI), or 27 microM L-nitroarginine. Nitrotyrosine:tyrosine ratios of slice extracts were measured using high-performance liquid chromatography. Cresyl violet-stained sections (2 microm) from random slices were examined histologically.

After 60 min of hypoxia, adenosine triphosphate decreased to < or = 3, < or = 3, 65 +/- 6, and 25 +/- 4% of control in slices that were untreated or treated with L-nitroarginine, L-NAME, and 7-NI, respectively. After 120 min of hyperoxic recovery, adenosine triphosphate levels returned to control values in slices pretreated with L-NAME and 7-NI, but to only 30% of control in untreated or L-nitroarginine-treated slices. Nitric oxide donors administered during posthypoxic recovery partially antagonized the adenosine triphosphate recovery found with L-NAME and 7-NI. Nitric oxide synthase activity in slice homogenates, assayed via conversion of L-arginine to citrulline, was < or = 2% of control after all inhibitory treatments. The nitrotyrosine:tyrosine ratio increased 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 swelling.

Neuronal NO is associated with rapid adenosine triphosphate reductions and peroxynitrite formation in acutely hypoxic cerebrocortical slices.