The use of angiotensin-converting enzyme inhibitors in congestive heart failure

Effects of long-acting angiotensin-converting enzyme inhibitor, imidapril, on the lower limit of cerebral blood flow autoregulation in hypertensive rats

The objective of the present study was to examine the effects of a long-acting angiotensin converting enzyme inhibitor, imidapril ((4S)-1-methyl-3-¿(2S)-2-[N-(1S)-1-ethoxycarbonyl-3-phenylpropyl) amino] propionyl¿-2-oxoimidazolidine-4-carboxylic acid hydrochloride), for 7 days on the cerebral blood flow autoregulatory response to hypotension in hypertensive rats. We measured the cerebral blood flow at rest and during hemorrhagic hypotension, using laser-Doppler flowmetry. At the same time, the absolute baseline cerebral blood flow values in the parietal cortex were quantified with the hydrogen clearance method. After administration of imidapril at a dose of 5 mg/kg/day for 7 days, the resting value of mean arterial blood pressure was significantly decreased by 25 mm Hg (P < 0.001), cerebral vascular resistance was lowered by 14.4% (P < 0.05) and the lower limit of cerebral blood flow autoregulation was shifted to a lower level, 106+/-11 mm Hg (mean +/- S.D.), from 137+/-8 mm Hg in the control group (P < 0.001), while resting cerebral blood flow remained unchanged. The present results demonstrated that imidapril preserves cerebral blood flow and significantly shifts the lower limit of cerebral autoregulation towards lower blood pressure levels.

Inhibition of angiotensin-converting enzyme modulates the autoregulation of regional cerebral blood flow in hypertensive rats

The inhibition of angiotensin-converting enzyme activities is considered to favorably modulate the hemodynamics of the brain. We designed the present study to examine the effects of angiotensin-converting enzyme inhibitors on regional differences in the lower limits of cerebral blood flow autoregulation in spontaneously hypertensive rats. Angiotensin-converting enzyme inhibitors (either 10 mg/kg captopril or SQ 29,852 in saline) were intravenously injected 15 minutes before hemorrhagic hypotension was induced. Cerebral blood flows to the parietal cortex and thalamus were simultaneously measured by hydrogen clearance. Both captopril and SQ 29,852 significantly decreased mean arterial pressure by 14 to 18 mm Hg and also reduced calculated cerebral vascular resistance by 11% to 15% of resting values, which resulted in a well-maintained cerebral blood flow. The lower limits of autoregulation were 76 +/- 2% (mean +/- SEM) and 77 +/- 2% of resting values in the cortex and thalamus, respectively, in control rats. Administration of either captopril or SQ 29,852 significantly reduced the lower limits to 65 +/- 3% (P < .01 versus control) and 67 +/- 2% (P < .05), respectively, in the cortex, which were slightly but always larger than the 71 +/- 3% and 71 +/- 2% reduction, respectively, in the thalamus. The inhibition of angiotensin-converting enzyme activities thus may be more protective against acute hypotension for cerebral microcirculation in the cortex than in the thalamus.