We have previously demonstrated a transitory
tachycardia during the early phase of one kidney, one
clip (1K1C)
hypertension in the rat, when the basal heart rate (HR) is measured daily under resting conditions. In the present study, in control rats, marked
tachycardia (406 +/- 11 vs 320 +/- 4 bpm during the control period) was observed on the first day of electrolytic lesion of the anteroventral third ventricle (AV3V) region. The basal HR declined progressively thereafter and was normal 14 days after AV3V lesion. The peak of
tachycardia (388 +/- 12 bpm) observed 7 days after clipping in
sham-lesioned rats did not occur in 1K1C AV3V-lesioned rats (318 +/- 5 bpm). However,
hypertension was only partially (65%) abolished in the lesioned animals (135 +/- 4 vs 160 +/- 3 mm Hg in the
sham-lesioned 1K1C).
Captopril administered per os (30 mg/kg/day) for up to 20 days produced no change in the basal HR of
sham-operated rats but abolished the initial
tachycardia in 1K1C rats during the development of
hypertension.
Captopril also delayed the onset of
renal hypertension, with mean arterial pressure reaching hypertensive levels only 2 weeks after clipping. These data indicate that integrity of the AV3V region is necessary for the occurrence of
tachycardia during the onset of 1K1C
hypertension. Since
captopril abolished the
tachycardia, the activity of converting
enzyme seems to be important for the appearance of this phenomenon.