Alteration in regional brain catecholamines during and after acute hemorrhage in the rat

Using high-performance liquid chromatography (HPLC), we carried out a simultaneous assay of norepinephrine (NE), epinephrine (E), and dopamine (DA) in specific brain regions before and at 5 min, 30 min, 1 hr, 2 hr, and 24 hr following acute hemorrhage in the rat. Thirty-six awake male Sprague-Dawley rats were subjected to rapid fixed-volume hemorrhage (8.5 ml/300 g) over 5 min. In the hypothalamus, concentrations of NE and E fell markedly and significantly by 5 min posthemorrhage (P < 0.001), while hypothalamic DA concentrations fell gradually to reach a nadir by 2 hr (P < 0.005). Hypothalamic concentrations of all three catecholamines remained significantly reduced up to 24 hr posthemorrhage. Dopamine concentrations in the medulla increased transiently, while striatal DA concentrations fell following hemorrhage to reach a nadir by 2 hr (P < 0.001). By 2 hr posthemorrhage, NE concentrations in both cortex and medulla were significantly decreased (P < 0.01 and P < 0.005, respectively), with cortical NE levels remaining significantly depressed for up to 24 hr. These results suggest that regional and prolonged changes occur in central catecholaminergic systems following acute, uncompensated hemorrhage. It is possible that these changes in the central nervous system contribute to the cardiovascular dysfunction observed following hemorrhage.