1. A reduced noradrenaline turnover rate has been previously demonstrated in the brain stem of deoxycorticosterone acetate (DOCA)-sodium hypertensive rats. In the present study, the turnover rate was measured in smaller brain regions and the effect of sodium depletion was studied on the turnover rate of these regions.

2. Catecholamine turnover rate was significantly reduced only in the pons, was slightly but not significantly reduced in the thoracic spinal cord and was normal in the upper and lower medulla oblongata, in the mesencephalon, in the hypothalamus and in the telencephalon.

3. The administration of a sodium-free diet for 3 weeks lowered significantly the blood pressure and concomitantly accelerated the turnover rate in the pons area of DOC A hypertensive rats.

4. It is concluded that pontine catecholaminergic fibres, sensitive to sodium balance, might be involved in the maintenance of DOCA-sodium hypertension in the rat.

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