We examined the dose-related effects of angiotensin-converting enzyme inhibitors on circulating and tissue levels of angiotensin and bradykinin peptides by administering perindopril or lisinopril to rats in drinking water for 7 days. A reduction in the ratio of plasma angiotensin II (Ang II) to Ang I was seen for 0.006 mg/kg per day perindopril, with an increase in plasma renin and Ang I at 0.017 mg/kg per day. Plasma Ang II levels did not decrease until 1.4 mg/kg per day perindopril, at which dose plasma Ang I levels reached a plateau of an approximate 25-fold increase. The effects of perindopril on Ang II and Ang I levels in heart, lung, aorta, and brown adipose tissue were parallel to those observed for plasma. By contrast, renal Ang I levels did not increase, and renal Ang II levels decreased by 40% at 0.017 mg/kg per day, the same threshold seen for the increase in plasma renin. Perindopril increased circulating bradykinin-(l-9) levels approximately eightfold, with a threshold dose of 0.052 mg/kg per day, and increased bradykinin-(l-9) levels in kidney, heart,

The bradykinin peptide system is a tissue-based system with potent cardiovascular and renal effects. To investigate the regulation of this system, we developed a highly sensitive amino terminal-directed radioimmunoassay that, with high performance liquid chromatography, enables the measurement of bradykinin-(l-7), bradykinin-(l-8), and bradykinin-(l-9). Together with a carboxy terminal-directed radioimmunoassay, we characterized bradykinin peptides in rat kidney and blood. The predominant bradykinin peptides in kidney were bradykinin-(l-9) (-100 fmol/g wet weight of tissue) and bradykinin-(1-7) (-70 fmol/g), with low levels of bradykinin-(l-8) (-8 fmol/g) and bradykinin-(4-9) (-12 fmol/g) detectable; bradykinin-(2-9) and bradykinin-(3-9) were below the limits of detection. In blood, the levels of bradykinin-(l-9) were very low (-2 fmol/ml), and other bradykinin peptides were below the limits of detection. Ue,Ser-bradykinin and Met,Ile,Ser-bradykinin were below the limits of detection in both kidney and blood, indicating that T-kininogen makes no detectable contribution to renal or circulating bradykinin peptides. Administration of the angiotensin converting enzyme inhibitor perindopril was associated with an approximate twofold increase in renal levels of bradykinin-(l-8) and bradykinin-(1-9) and a decrease in the bradykinin-(l-7)/bradykinin-(l-9) ratio. The amino terminal-directed radioimmunoassay was also applied to heart, aorta, brown adipose tissue, adrenal, lung, and brain. For these tissues, bradykinin-(l-7) and bradykinin-(l-9) were of similar abundance (16-340 fmol/g), with lower levels of bradykinin-(l-8). These studies demonstrate that tissue levels of bradykinin peptides are much higher than circulating levels, consistent with their formation at a local tissue site. Of peptides derived from K-kininogen, bradykinin-(l-9) is the predominant bioactive peptide in all tissues, and a major pathway of bradykinin-(l-9) metabolism involves the formation of bradykinin-(l-7). In kidney, angiotensin converting enzyme plays an important role in bradykinin-(l-9) metabolism, and increased bradykinin-(l-9) and bradykinin-(l-8) levels may mediate in part the renal effects of converting enzyme inhibition. BK-(l-9)] has important actions on blood vessels, the heart, and kidney. By far the most important hemodynamic effect of BK-(l-9) in vivo is the hypotensive vasodilation produced by stimulation of endothelial B 2 receptors of arteries and arterioles, with subsequent endothelial release of nitric oxide and prostaglandins.1 -4 Additional renal actions of BK-(l-9) include the production of a diuresis and natriuresis. 5 " 8 Evidence that endogenous bradykinin peptides influence blood pressure and renal function includes the hypertensive effect of bradykinin antagonists in normotensive 9 -12 and hypertensive 1314 rats and the decrease in renal blood flow and glomerular filtration rate in response to aprotinin (a nonspecific serine protease inhibitor that inhibits renal kallikrein) and bradykinin antagonists.uu.is-n En...

The kinin peptide system in humans is complex. Whereas plasma kallikrein generates bradykinin peptides, glandular kallikrein generates kallidin peptides. Moreover, a proportion of kinin peptides is hydroxylated on proline(3) of the bradykinin sequence. We established HPLC-based radioimmunoassays for nonhydroxylated and hydroxylated bradykinin and kallidin peptides and their metabolites in blood and urine. Both nonhydroxylated and hydroxylated bradykinin and kallidin peptides were identified in human blood and urine, although the levels in blood were often below the assay detection limit. Whereas kallidin peptides were more abundant than bradykinin peptides in urine, bradykinin peptides were more abundant in blood. Bradykinin and kallidin peptide levels were higher in venous than arterial blood. Angiotensin-converting enzyme inhibition increased blood levels of bradykinin, but not kallidin, peptides. Reactive hyperemia had no effect on antecubital venous levels of bradykinin or kallidin peptide levels. These studies demonstrate differential regulation of the bradykinin and kallidin peptide systems, and indicate that blood levels of bradykinin peptides are more responsive to angiotensin-converting enzyme inhibition than blood levels of kallidin peptides.

To determine the contribution of kidney-derived renin and angiotensin converting enzyme to circulating and tissue levels of angiotensin peptides, we measured angiotensin (Ang)-(l-7), Ang n, Ang-(l-9), and Ang I in plasma, kidney, lung, heart, aorta, brown adipose tissue, adrenal, pituitary, and brain of five groups of male Sprague-Dawley rats: control rats, rats given the converting enzyme inhibitor ramipril (10 mg/kg), rats nephrectomized 24 hours, rats nephrectomized 48 hours, and rats nephrectomized 48 hours and given ramipril. Plasma and tissues, apart from adrenal, showed a 63% to 98% reduction in Ang II, the ratio of Ang II to Ang I, or both after ramipril administration, indicating a major role for converting enzyme in Ang II formation. Nephrectomy caused a more than 95% decrease in plasma renin levels and a fourfold to eightfold increase in plasma angiotensinogen levels. Apart from plasma and brain, tissues showed a 59% to 78% decrease in Ang II levels after nephrectomy, indicating a major role for kidney-derived renin in Ang II formation. The persistence of Ang II in plasma and tissues of anephric rats indicates that Ang II may be formed by a process independent of kidney-derived renin; this process may be amplified by the increased plasma angiotensinogen levels that accompany nephrectomy. For lung, adrenal, and aorta, Ang II levels showed a further decrease when nephrectomized rats were given ramipril. However, for plasma and the other tissues, ramipril produced little or no decrease in Ang II levels of anephric rats, suggesting that Ang II may be formed by a pathway independent of converting enzyme. Such a pathway may involve the direct formation of Ang II from angiotensinogen by a non-reninlike enzyme. (Hypertension. 199322:513-522.) KEY WORDS • angiotensin high-performance liquid II • angiotensin I • radioimmunoassay • chromatography, A ngiotensin II (Ang II) plays a major role in the / \ regulation of blood pressure and fluid and elec-X \ -trolyte homeostasis. In addition to the circulating renin-angiotensin system, a large body of evidence indicates that tissues are a major site of Ang II formation and that they make an important contribution to circulating levels of angiotensin I (Ang I) and Ang II.

The renin-angiotensin system has been implicated in the pathogenesis of hypertension in spontaneously hypertensive rats (SHR). Given that SHR may have normal or suppressed plasma levels of renin and angiotensin peptides, we examined whether the tissue levels of angiotensin peptides are elevated in these rats. We measured angiotensin-(1-7) [Ang-(1-7)], Ang II, and Ang I in plasma, kidney, adrenal, heart, aorta, brown adipose tissue, lung, and brain of male SHR and normotensive Donryu rats at 6, 10, and 20 weeks of age. SHR had higher blood pressures and ratios of heart weight to body weight at all ages. Plasma renin levels of SHR were 13% to 32% of the levels of Donryu rats. Although plasma angiotensin-converting enzyme activity was lower in SHR than in Donryu rats, lung was the only SHR tissue with a reduced Ang II-Ang I ratio. Ang II levels in SHR adrenal were 24% to 42% of the levels of Donryu adrenal, and for SHR plasma, aorta, brown adipose tissue, and lung, Ang II levels were 38% to 93% of the levels of Donryu rats. For kidney and heart, Ang II levels were similar in SHR and Donryu rats at 6 weeks of age although suppressed in SHR at 10 and 20 weeks. Moreover, brain Ang II levels were higher in SHR than Donryu rats at 6 weeks of age and similar at 10 and 20 weeks of age.(ABSTRACT TRUNCATED AT 250 WORDS)