Chronic lability of arterial pressure in the rat does not evolve into hypertension.

1. In rats, electrolytic lesions of the A2 group of catecholamine neurons result in lability of arterial pressure without hypertension. 2. To establish whether labile arterial pressure, when chronic, will lead to fixed hypertension, we placed lesions in the A2 area of adult male Sprague-Dawley rats and measured mean arterial pressure, heart rate and their variability (expressed as the standard deviation) 11 months later. Controls were age-matched, unoperated or sham-operated rats. 3. In rats with A2 lesions: (a) the mean arterial pressure was lower (103 +/- 7.5 mmHg; n = 6; P < 0.05) than in sham-operated (123 +/- 4.7 mmHg; n = 4) or unoperated (120 +/- 3.1 mmHg; n = 9) controls; (b) the standard deviation of mean arterial pressure was higher (16 +/- 1.8 mmHg; P < 0.001) than in sham-operated (5 +/- 0.7 mmHg) or unoperated controls (7 +/- 0.6 mmHg); (c) the mean and standard deviation of heart rate did not differ between groups. No histopathological changes were detected in the A2 group. 4. Chronic lability of arterial pressure does not evolve into sustained hypertension nor does it induce systemic lesions.