enalaprilat-anhydrous and renin-inhibitory-peptide

Topics: Adult; Dose-Response Relationship, Drug; Double-Blind Method; Enalaprilat; Humans; Injections, Intradermal; Male; Microcirculation; Oligopeptides; Regional Blood Flow; Renin; Skin

In order to investigate the hypotensive mechanisms of action of peptide renin inhibitors, blood pressure responses to five renin inhibitors were compared with those to the angiotensin converting enzyme inhibitor, enalaprilat, in conscious African green and rhesus monkeys. (3S-4S)-4-amino-5-cyclohexyl-3-hydroxy pentanoic acid (ACHPA)-containing renin inhibitory peptide (ACRIP) and enalaprilat both decreased blood pressure in euvolemic and volume-depleted African green monkeys. However, while a maximum dose of enalaprilat reduced blood pressure to 80 +/- 4 and 56 +/- 4 mmHg in the euvolemic and volume-depleted monkeys, respectively, ACRIP lowered pressure to life-threatening levels (less than 40 mmHg) under both conditions. The relative potencies of ACRIP and four other renin inhibitors for inhibiting in vitro plasma renin activity (PRA; IC50) were compared with their potencies in reducing blood pressure by 15 mmHg (ED15 mmHg) and lowering blood pressure more than enalaprilat in volume-depleted rhesus monkeys. All renin inhibitors lowered blood pressure significantly beyond the maximal response to enalaprilat. Despite a significant correlation (r = 0.99, P less than 0.05) between the in vitro PRA inhibitory potency and the in vivo ED15 mmHg, doses which lowered blood pressure beyond the maximal responses to enalaprilat were not significantly correlated (r = 0.53, P greater than 0.05) with the in vitro PRA IC50 values. Furthermore, the profound depressor responses to renin inhibitors in rhesus monkeys were accompanied by increases in the heart rate and decreases in pulse pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Blood Pressure; Blood Volume; Chlorocebus aethiops; Enalaprilat; Female; Heart Rate; Macaca mulatta; Male; Oligopeptides; Renin; Renin-Angiotensin System

The effects of angiotensin II and its precursors angiotensin I and tetradecapeptide renin substrate were investigated in isolated segments of the rat caudal artery. Each peptide constricted the rat caudal artery and also enhanced vasoconstrictor responses to sympathetic nerve stimulation (0.5 Hz, 10 s). The threshold concentrations for each peptide in enhancing sympathetic vasoconstrictor responses were lower than those required to produce vasoconstriction. Tetradecapeptide renin substrate was the least potent of the three peptides and had the slowest onset of action. Angiotensin II and angiotensin I each enhanced noradrenergic transmission to the same degree, whether perfused through the lumen or added to the adventitial surface of the artery. In contrast, tetradecapeptide renin substrate was more potent when applied to the adventitial surface. The effects of angiotensin I were blocked by the converting enzyme inhibitor enalaprilat, whereas the effects of tetradecapeptide renin substrate were unaltered by enalaprilat, or by the renin inhibitors pepstatin or a decapeptide renin inhibitor. These findings suggest that tetradecapeptide renin substrate and angiotensin I may be converted to angiotensin II within the rat caudal artery, with subsequent enhancement of noradrenergic neuroeffector function. However, the enzyme responsible for the conversion of tetradecapeptide renin substrate cannot be determined from the present findings.

Topics: Angiotensin I; Angiotensin II; Angiotensinogen; Animals; Arteries; Enalapril; Enalaprilat; Female; Male; Neurotransmitter Agents; Oligopeptides; Rats; Rats, Inbred Strains; Tail