Alteration of Rat Brain Catecholamine Metabolism During Exposure to Hypobaric Hypoxia

Abstract

The effect of hypobaric hypoxia on the metabolism of brain catecholamines in the rat was studied using intracisternal injections of 3H-tyrosine (3H-TYR) and 3H-dihydroxyphenylalanine (3H-DOPA) and intraperitoneal injections of α-methyltyrosine. Adult male Sprague–Dawley rats were housed singly or in pairs in barometric chambers and either maintained as controls or exposed to a hypoxic environment (380 mm Hg) for periods ranging up to 30 h. Whole brain norepinephrine (NE) and dopamine (DA) concentrations were significantly less than controls after exposures of 6, 12, and 18 h and normal after 24 h. Significant increases in specific activity of 3H-NE and 3H-DA derived from 3H-DOPA were obtained from brains of animals exposed for 6–18 h. The increase in 3H-NE specific activity was also evident with exposures lasting up to 30 h. Levels of 3H-NE derived from 3H-TYR were also increased with 12 h exposure when compared to controls. Turnover rates of NE, determined after pool size returned to normal (24 h), were not altered. Changes in cerebrospinal fluid composition, flow, and pressure may be responsible for the observed increases in 3H-NE derived from 3H-TYR or 3H-DOPA.