1. The time course of changes in baroreceptor reflex sensitivity during the development of renovascular hypertension was studied in male Wistar rats in which the left renal arteries were constricted by silver wire clips of 0.18 mm internal diameter.

2. Groups of animals were studied at 3, 7, 14 and 25 days after induction of renovascular hypertension. Rats of comparable ages were included as controls. There was a significant decrease in mean baroreflex sensitivity from 0.950 ± 0.157 ms/mmHg (n = 8) in the normal control group to 0.537 ± 0.105 ms/mmHg (n = 8) in the 3 day hypertensive group (P < 0.05). Baroreflex sensitivity in the 3 day hypertensive rats was independent of the level of arterial pressure achieved in individual animals.

3. These changes in baroreflex sensitivity at 3 days precede the development of left ventricular hypertrophy and, as previously shown in this model, also precede structural vascular adaptation and resetting of the carotid sinus baroreceptor threshold.

4. A further loss of baroreflex sensitivity, which may be structurally based, occurred later. Baroreflex sensitivity in the 14 day hypertensive rats fell to 0.182 ± 0.039 ms/mmHg (n = 8) compared with the 3 day hypertensive rats (P < 0.01).

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