Changes in cardiac and hypothalamic noradrenergic activity with taurine in DOCA-salt rats

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Abstract
We studied the role of the cardiac and hypothalamic noradrenergic systems in the hypotensive actions of dietary taurine supplementation in deoxycorticosterone acetate (DOCA)-salt rats. The supplementation with 1% taurine could reduce blood pressure when it was given after DOCA-salt hypertension had been established. The taurine supplementation could attenuate the increased depressor response to hexamethonium-induced ganglion blockade in the DOCA-salt rats. Moreover, noradrenergic activity was determined from the rate of decline of tissue norepinephrine (NE) concentration after the administration of alpha-methyl-p-tyrosine. At 23 degrees C, cardiac NE turnover was markedly accelerated in DOCA-salt rats compared with the vehicle-injected control rats, but the 1% taurine supplement restored it toward normal. In contrast, turnover time in the hypothalamus was delayed in the DOCA-salt rats compared with the control rats, whereas 1% taurine supplement normalized the hypothalamic NE turnover. Stimulation of sympathetic discharge by cold exposure (4 degrees C, 6 h) after the administration of alpha-methyl-p-tyrosine produced marked depletion of NE in most tissues. The NE deficit in both the hypothalamus and heart was significantly greater in the DOCA-salt rats than in the control rats, but the 1% taurine supplement could normalize this. Thus taurine loading could not only diminish the sympathetic overactivity under the normal condition but also attenuate the augmented hypothalamic and cardiac noradrenergic activity by cold stress in the DOCA-salt hypertensive rats. Evidence presented suggests, therefore, that the hypothalamic noradrenergic system might be involved in the hypotensive action of taurine in DOCA-salt rats.