1. After 4–5 months of renal hypertension in rats renal artery ‘declipping’ was performed. Eight weeks afterwards paired hindquarter perfusions were performed on the declipped rats and normotensive control rats, exploring the relationships between mean arterial pressure and flow, from maximal vasodilatation to maximal vasoconstriction, induced by graded noradrenaline infusions. Left ventricular weights were measured.

2. Declipping caused a fall in mean arterial pressure from 180 to 135 mmHg, though still after 8 weeks the mean pressure was 19% higher than in normotensive control rats.

3. All parameters reflecting design and reactivity of the resistance vessels and left ventricular weight decreased significantly, but not as much as mean arterial pressure, and were still significantly increased compared with those of control rats.

4. Thus neither mean arterial pressure nor cardiovascular design was normalized 8 weeks after ‘reversal’ of long-standing renal hypertension, in contrast to short-standing renal hypertension where both are completely normalized 3 weeks after declipping.

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