Plasma Angiotensins and Blood Pressure During Converting Enzyme Inhibition

• Published in: Hypertension (Dallas, Tex. 1979) Vol. 9; no. 6, Part 2 Suppl III; pp. III-42 - III-48
• Main Authors: MENTO, PETER F, WILKES, BARRY M
• Format: Journal Article
• Language: English
• Published: Philadelphia, PA American Heart Association, Inc 01-06-1987; Hagerstown, MD Lippincott
• Subjects: Angiotensin II - blood; Angiotensin-Converting Enzyme Inhibitors; Animals; Applied sciences; Blood Pressure - drug effects; Chromatography, High Pressure Liquid; Enalapril - pharmacology; Exact sciences and technology; Male; Osmolar Concentration; Other techniques and industries; Peptide Fragments - blood; Radioimmunoassay; Rats; Rats, Inbred Strains
• ISSN: 0194-911X; 1524-4563
• DOI: 10.1161/01.HYP.9.6_Pt_2.III42

The relationship between plasma angiotensin and the reduction of blood pressure with the angiotensin converting enzyme inhibitor enalapril was studied in rats. Blood pressure was measured in conscious rats with indwelling arterial catheters. To measure angiotensin II, plasma was analyzed by physical separation of angiotensins using high performance liquid chromatography followed by radioimmunoassay. The effects of both single (acute) and long-term (chronic) dosages of enalapril were measured. After a single oral dose of enalapril (10 mg/kg), mean arterial pressure fell from 111 ± 3 to 86 ± 3 nun Hg (p < 0.005). Despite the blood pressure reduction, plasma angiotensin II was unaffected (control, 9.9 ± 1.8 vs 9.7 ±1.1 pg/ml). After a higher single oral dose of enalapril (30 mg/kg), there was a reduction in both mean arterial pressure (81 ± 5 mm Hg, p < 0.005) and plasma angiotensin II concentration (2.3 ± 0.6 pg/ml, p < 0.01). The chronic effects of converting enzyme inhibition were evaluated in rats given enalapril in their drinking water (30 mg/kg/24 hr) for 1 week or 2 months. Mean arterial pressure remained equally low after chronic administration (for 1 week or 2 months), but plasma angiotensin II increased above normal (after 1 week, 28.9 ±8.7, p < 0.01 vs control; after 2 months, 43.1 ± 16.2 pg/ml, p < 0.05 vs control). Although plasma angiotensin converting enzyme activity was undetectable at any time after enalapril administration, there was a partial return of the angiotensin I pressor response with chronic administration. The data are most compatible with actions of converting enzyme inhibitors independent of the blockade of plasma angiotensin II formation.