Noradrenaline synthesis, release and vesicular transport in the rat brain following subarachnoid haemorrhage.

The present study was designed to estimate the release of noradrenaline, and to evaluate the efficiency of noradrenaline vesicular transport, as indicated from measures of dihydroxyphenylglycol (DHPG), and synthesis in the medulla and hypothalamus following subarachnoid haemorrhage in rats. Subarachnoid haemorrhage was induced by the injection of homologous blood into the cisterna magna (n = 11). Sham operated animals served as controls (n = 11). Three days following subarachnoid haemorrhage, medulla and hypothalamus were dissected and placed in an in vitro superfusion system. Exposure to K(+) (50 mM) for 2 min served as a stimulus for the release of the neurotransmitter noradrenaline, its precursor (dihydroxyphenylalanine [DOPA]) and intraneuronal metabolite, DHPG. Basal noradrenaline overflow from both the medulla and hypothalamus were similar in the two groups of rats but basal DOPA overflow from the medulla was significantly reduced in the subarachnoid haemorrhage animals (0.97 +/- 0.15 vs. 1.97 +/- 0.38 pg/10 min/mg, p < 0.01). Administration of K(+) induced the release of noradrenaline, the response from the medulla in the subarachnoid haemorrhage group being attenuated (p < 0.01) compared with the sham operated animals (174% and 240%, respectively). K(+) induced a similar release of noradrenaline from the hypothalamus in both groups of rats (239% in sham animals and 283% in the subarachnoid haemorrhage group). The overflow of DHPG from both the hypothalamus and medulla was similar in both groups of animals. Our results suggest that the diminution in noradrenaline release from the medulla occurs as a result of a reduction in the rate of noradrenaline synthesis and release.