Observations on the blood pressure lowering mechanism of diuretics

The haemodynamic effects of short-time (3-7 days) and longer (2-3 months) periods of saliuretic treatment were investigated in several groups of patients with uncomplicated essential hypertension. Short-time salt depletion results in decrease of cardiac index, extracellular and blood volumes and marked increases in plasma renin activity (PRA) and noradrenaline excretion, while blood pressure (BP) becomes "renin dependent"as assessed by an angiotensin I antagonist (P 113). The BP decrease was only moderate and variable, due to increased peripheral resistance, and could not be related either to control PRA values or degree of subsequent elevation. After longer treatment periods, all of the above-mentioned changes are still present, but less pronounced while BP decreases further. At that time a clear distinction can be made between the patients who do and those who do not "respond" with a BP drop. The non responders tend to remain in a salt and fluid depleted state with a renin dependent BP, while in the responders the initially induced hemodynamic changes have largely, but not completely, disappeared.