Increased tissue kallikrein levels in type 2 diabetes.

AIMS/HYPOTHESIS: We measured components of the kallikrein- kinin system in human type 2 diabetes mellitus and the effects of statin therapy on the circulating kallikrein-kinin system. METHODS: Circulating levels of bradykinin and kallidin peptides, and high and low molecular weight kininogens, as well as plasma and tissue kallikrein, and kallistatin were measured in non-diabetic and diabetic patients before coronary artery bypass graft surgery. Tissue kallikrein levels in atrial tissue were examined by immunohistochemistry and atrial tissue kallikrein mRNA quantified. RESULTS: Plasma levels of tissue kallikrein were approximately 62% higher in diabetic than in non-diabetic patients (p=0.001), whereas no differences were seen in circulating levels of bradykinin and kallidin peptides, and high and low molecular weight kininogens, or in plasma kallikrein or kallistatin. Immunohistochemistry revealed a twofold increase in tissue kallikrein levels in atrial myocytes (p= 0.015), while tissue kallikrein mRNA levels were increased eightfold in atrial tissue of diabetic patients (p=0.014). Statin therapy did not change any variables of the circulating kallikrein-kinin system. Neither aspirin, calcium antagonists, beta blockers or long-acting nitrate therapies influenced any kallikrein-kinin system variable. CONCLUSIONS/INTERPRETATION: Tissue kallikrein levels are increased in type 2 diabetes, whereas statin therapy does not modify the circulating kallikrein-kinin system. Cardiac tissue kallikrein may play a greater cardioprotective role in type 2 diabetic than in non-diabetic patients and contribute to the benefits of ACE inhibitor therapy in type 2 diabetic patients. However, our findings do not support a role for the kallikrein-kinin system in mediating the effects of statin therapy on endothelial function.

Activation of the kallikrein-kinin system by cardiopulmonary bypass in humans.

We used cardiopulmonary bypass (CPB) as a model of activation of the contact system and investigated the involvement of the plasma and tissue kallikrein-kinin systems (KKS) in this process. Circulating levels of bradykinin and kallidin and their metabolites, plasma and tissue kallikrein, low and high molecular weight kininogen, and kallistatin were measured before, during, and 1, 4, and 10 h after CPB in subjects undergoing cardiac surgery. Bradykinin peptide levels increased 10- to 20-fold during the first 10 min, returned toward basal levels by 70 min of CPB, and remained 1.2- to 2.5-fold elevated after CPB. Kallidin peptide levels showed little change during CPB, but they were elevated 1.7- to 5.2-fold after CPB. There were reductions of 80 and 60% in plasma and tissue kallikrein levels, respectively, during the first minute of CPB. Kininogen and kallistatin levels were unchanged. Angiotensin-converting enzyme inhibition did not amplify the increase in bradykinin levels during CPB. Aprotinin administration prevented activation of the KKS. The changes in circulating kinin and kallikrein levels indicate activation of both the plasma and tissue KKS during activation of the contact system by CPB.

Kinins in humans.

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.

Angiotensin-converting enzyme inhibition modifies angiotensin but not kinin peptide levels in human atrial tissue.

Angiotensin-converting enzyme (ACE) converts angiotensin I (Ang I) to angiotensin II (Ang II) and metabolizes bradykinin and kallidin peptides. Decreased Ang II levels and increased kinin peptide levels are implicated in the mediation of the therapeutic effects of ACE inhibition. However, alternative non-ACE pathways of Ang II formation have been proposed to predominate in human heart. We investigated the effects of ACE inhibition on cardiac tissue levels of angiotensin and kinin peptides. High-performance liquid chromatography-based radioimmunoassays were used to measure angiotensin peptides and hydroxylated and nonhydroxylated bradykinin and kallidin peptides in right atrial appendages of subjects who had been prepared for cardiopulmonary bypass. Peptide levels in subjects who received ACE inhibitor therapy were compared with those who did not receive ACE inhibitor therapy. ACE inhibition reduced Ang II levels, which was associated with an 80% reduction in the Ang II/Ang I ratio. ACE inhibition did not modify either bradykinin or kallidin peptide levels or the bradykinin-(1-7)/bradykinin-(1-9) ratio. The 80% reduction in the Ang II/Ang I ratio by ACE inhibition indicated a primary role for ACE in the conversion of Ang I to Ang II in atrial tissue. These data support a role for reduced Ang II levels but do not support a role for increased kinin peptide levels in mediating the direct cardiac effects of ACE inhibition.

Type 2 bradykinin-receptor antagonism does not modify kinin or angiotensin peptide levels.

Type 2 bradykinin (B2)-receptor antagonists have been used to define the role of endogenous kinin peptides. However, interpretation of the effects of B2-receptor antagonists has been limited by lack of information concerning the effects of these antagonists on endogenous kinin and angiotensin peptide levels. If kinin levels were subject to short-loop-feedback regulation mediated through B2 receptors, then a reactive increase in kinin levels might blunt the effects of B2-receptor antagonism and stimulate type 1 bradykinin receptors. Moreover, kinins have been implicated in the control of renin secretion. We investigated whether endogenous kinin levels are subject to short-loop-feedback regulation mediated by the B2 receptor and whether endogenous kinins acting through the B2 receptor influence plasma renin levels and circulating and tissue angiotensin peptide levels. The B2-receptor antagonist icatibant (1 mg/kg) was administered to rats by intraperitoneal injection, and circulating and tissue levels of angiotensin and kinin peptides were measured after 4 hours. Icatibant produced 75% occupancy of B2 receptors in the inner stripe of the renal medulla. Icatibant did not influence plasma levels of renin, angiotensinogen, angiotensin-converting enzyme, neutral endopeptidase, or circulating or tissue levels of angiotensin and bradykinin peptides. This study demonstrated that kinin levels are not subject to short-loop-feedback regulation mediated through B2 receptors and that endogenous kinin levels acting through the B2 receptor do not modulate the renin-angiotensin system.

Interaction between neutral endopeptidase and angiotensin converting enzyme inhibition in rats with myocardial infarction: effects on cardiac hypertrophy and angiotensin and bradykinin peptide levels.

Combined inhibition of neutral endopeptidase 24.11 (NEP) and angiotensin converting enzyme (ACE) is a candidate therapy for hypertension and cardiac failure. Given that NEP and ACE metabolize angiotensin (Ang) and bradykinin (BK) peptides, we investigated the effects of NEP inhibition and combined NEP and ACE inhibition on Ang and BK levels in rats with myocardial infarction. We administered the NEP inhibitor ecadotril (0, 0.1, 1, 10, and 100 mg/kg/day), either alone or together with the ACE inhibitor perindopril (0.2 mg/kg/day) by 12-hourly gavage from day 2 to 28 after infarction. Ecadotril increased urine cyclic GMP and BK-(1-9) excretion. Perindopril potentiated the effect of ecadotril on urine cyclic GMP excretion. Neither perindopril nor ecadotril reduced cardiac hypertrophy when administered separately, whereas the combination of perindopril and 10 or 100 mg/kg/day ecadotril reduced heart weight/body weight ratio by 10%. Administration of ecadotril to perindopril-treated rats decreased plasma Ang-(1-7) levels, increased cardiac BK-(1-9) levels, and increased Ang II levels in plasma, kidney, aorta, and lung. These data demonstrate interactions between the effects of NEP and ACE inhibition on remodeling of the infarcted heart and on Ang and BK peptide levels. Whereas increased cardiac BK-(1-9) levels may contribute to the reduction of cardiac hypertrophy, the reduction in plasma Ang-(1-7) levels and increase in Ang II levels in plasma and tissues may compromise the therapeutic effects of combined NEP/ACE inhibition.

Effects of neutral endopeptidase inhibition and combined angiotensin converting enzyme and neutral endopeptidase inhibition on angiotensin and bradykinin peptides in rats.

The combination of neutral endopeptidase 24.11 (NEP) and angiotensin converting enzyme (ACE) inhibition is a candidate therapy for hypertension and cardiac failure. Given that NEP and ACE metabolize angiotensin (Ang) and bradykinin (BK) peptides, we investigated the effects of NEP inhibition and combined NEP and ACE inhibition on the levels of these peptides. We administered the NEP inhibitor ecadotril (0, 0.1, 1, 10, 100 mg/kg per day), either alone or together with the ACE inhibitor perindopril (0.2 mg/kg per day), to rats by 12 hourly gavage for 7 days. Ecadotril produced diuresis, natriuresis, increased urine cyclic guanosine monophosphate and BK-(1-9) levels, increased Ang II and Ang I levels in plasma, and increased Ang I levels in heart. Perindopril reduced Ang II levels in kidney, and increased BK-(1-9) levels in blood, kidney and aorta. Combined NEP/ACE inhibition produced the summation of these effects of separate NEP and ACE inhibition. In addition, perindopril potentiated the ecadotril-mediated diuresis, natriuresis and decrease in urine BK-(1-7)/BK-(1-9) ratio, which is an index of BK-(1-9) metabolism. Moreover, combined NEP/ACE inhibition increased Ang II levels in plasma and lung. These data indicate that summation of the effects of separate NEP and ACE inhibition provides the basis for the therapeutic efficacy of their combination. Whereas potentiation by perindopril of the diuretic and natriuretic effects of ecadotril may contribute to the therapeutic effects, increased Ang II levels in plasma and lung may compromise the therapeutic effects of combined NEP/ACE inhibition.

Marked difference between angiotensin-converting enzyme and neutral endopeptidase inhibition in vivo by a dual inhibitor of both enzymes.

Dual inhibition of neutral endopeptidase 24.11 (NEP) and angiotensin-converting enzyme (ACE) offers the potential for improved therapy of hypertension and cardiac failure. S 21402-1 [(2S)-2-[(2S,3R)-2-thiomethyl-3-phenylbutanamido] propionic acid] is a sulfhydryl-containing potent inhibitor of both NEP (Ki = 1.7 nM) and ACE (Ki = 4.5 nM). S 21402-1 and the sulfhydryl-containing ACE inhibitor captopril were administered to rats by intraperitoneal injection (0, 0.3, 3, 30, 300 mg/kg). Urine was collected for 4 h; then plasma and kidneys were collected. The difference in NEP and ACE inhibition by S 21402-1 in vivo was greater than 1000-fold. All doses of S 21402-1 inhibited NEP, as indicated by plasma NEP activity, radioinhibitor binding to kidney sections, urinary sodium excretion and bradykinin-(1-7)/bradykinin-(1-9) ratio. However, only 300 mg/kg S 21402-1 inhibited ACE, as indicated by plasma angiotensin II/angiotensin I ratio, renin and angiotensinogen levels. Although S 21402-1 (30 and 300 mg/kg) inhibited renal NEP, as indicated by the bradykinin-(1-7)/bradykinin-(1-9) ratio in kidney, S 21402-1 had no effect on renal ACE, as indicated by the angiotensin II/angiotensin I ratio in kidney. Moreover, captopril was greater than 10-fold more potent than S 21402-1 as an ACE inhibitor in vivo. In separate experiments, the pressor response of anesthetized rats to angiotensin I showed more rapid decay in ACE inhibition by S 21402-1 than by captopril. These studies indicated that in vivo modification of S 21402-1 caused a much greater decrease in potency of ACE inhibition than NEP inhibition. Consequently, effective ACE inhibition by S 21402-1 required doses much higher than those required for NEP inhibition.

Angiotensin and bradykinin peptides in rats with myocardial infarction.

BACKGROUND: Angiotensin II (Ang II) stimulates cardiac hypertrophy and fibrosis, whereas bradykinin [BK-(1-9)] has cardioprotective actions and reduces infarct size following myocardial infarction. METHODS AND RESULTS: We investigated whether myocardial infarction and cardiac failure are associated with changes in circulating and tissue levels of angiotensin and bradykinin peptides. Myocardial infarction was produced in rats by coronary artery ligation and confirmed by electrocardiogram. Ang II, Ang I, BK-(1-9), and its metabolite BK-(1-7) were measured 1, 2, 3, 7, and 28 days after myocardial infarction. In comparison with sham operated rats, myocardial infarction reduced blood pressure and body weight, and produced cardiac hypertrophy and cardiac failure. Myocardial infarction increased plasma renin and ACE activity, reduced plasma angiotensinogen, and increased Ang II levels in plasma, aorta, kidney, and lung. Ang II levels in whole cardiac ventricles were similar in infarct and sham operated rats, but were positively correlated with heart weight/body weight ratio in infarct rats 3, 7, and 28 days after infarction. In a separate study of cardiac regions, Ang II levels were similar in infarct and sham operated rats, except at 7 days post surgery when right ventricular Ang II levels were higher in infarct rats. In infarct rats, Ang II levels were higher in the right ventricle and in the infarct than in the non-infarcted left ventricle at 7 days, but these differences were not apparent at 28 days after infarction. BK-(1-9) levels were increased in the heart and lung on days 2 and 3 post infarction, but not in the aorta or kidney. A decrease in BK-(1-7)/BK-(1-9) ratio suggested reduced metabolism of BK-(1-9) to BK-(1-7) in infarcted hearts. CONCLUSIONS: The transient activation of the circulating renin angiotensin system, and increased Ang II levels in the aorta, kidney, and lung may contribute to the systemic responses to myocardial infarction and cardiac failure. The correlations between cardiac Ang II levels and heart weight/body weight ratio noted for whole cardiac ventricles support a role for local Ang II levels in the process of myocardial remodeling post infarction. The increased cardiac BK-(1-9) levels in the acute phase of myocardial infarction were consistent with a role for this peptide in cardioprotection and limitation of infarct size.

Effects of angiotensin-converting enzyme inhibition on angiotensin and bradykinin peptides in rats with myocardial infarction.

Angiotensin-converting enzyme (ACE) inhibitors reduce myocardial remodeling and improve cardiac function after myocardial infarction. We investigated whether the beneficial effects of ACE inhibition were associated with changes in the levels of angiotensin and bradykinin peptides in blood, heart, lung, aorta, and kidney. Rats subjected to coronary artery ligation and selected by ECG criteria to have moderate to large myocardial infarctions (mean size, 38%) were administered perindopril (0, 20, 200, and 2,000 micrograms/kg/day) in their drinking water from the second day after surgery for 26 days. Perindopril caused a dose-related decrease in blood pressure and inhibited the development of both cardiac hypertrophy (estimated by heart weight/body weight ratio) and cardiac failure (estimated by lung weight/body weight ratio). Perindopril inhibited plasma ACE activity and increased plasma renin, with an associated decrease in plasma angiotensinogen. Plasma and all tissues showed a marked reduction in angiotensin II/angiotensin I ratio, indicating effective inhibition of ACE in plasma and tissues. Whereas heart, lung, and kidney showed dose-related decreases in angiotensin II (Ang II) levels, plasma and aortic levels of Ang II were not altered by perindopril. Perindopril increased blood bradykinin levels but did not increase bradykinin levels in heart, lung, aorta, or kidney. Heart showed a 45% increase in bradykinin levels at the highest dose of perindopril, which did not achieve statistical significance, although perindopril reduced the bradykinin(1-7)/ bradykinin-(1-9) ratio in heart, indicating inhibition of cardiac metabolism of bradykinin by perindopril. By contrast, perindopril reduced bradykinin levels in lung. These data support a role for reduced blood pressure and cardiac Ang II levels in mediating the effects of ACE inhibition after myocardial infarction but do not support a role for tissue bradykinin in this process.

Converting enzyme inhibition and its withdrawal in spontaneously hypertensive rats.

When spontaneously hypertensive rats (SHR) treated at a young age with an inhibitor of angiotensin-converting enzyme (ACE) are withdrawn from treatment, their blood pressure (BP) remains below that of untreated rats. We examined the effects of ACE inhibitor treatment and its withdrawal on angiotensin-(1-7) [Ang-(1-7)], angiotensin II (Ang II) and angiotensin I (Ang I) in plasma, kidney, adrenal, heart, aorta, brown adipose tissue, lung, and brain of male SHR and normotensive Donryu rats. Rats were administered either vehicle or perindopril (3 mg/kg/day) from 6 to 10 weeks, from 6 to 20 weeks, and from 6 to 10 weeks, followed by perindopril withdrawal from 10 to 20 weeks. Angiotensin peptides and plasma levels of renin, angiotensinogen, ACE, and aldosterone were measured at 10 and 20 weeks of age. Perindopril reduced BP of both SHR and Donryu rats, although only SHR showed a reduction of BP of 19 mm Hg after perindopril withdrawal, associated with a reduction of 5% in heart weight/body weight ratio. Perindopril reduced the angiotensin II/angiotensin I ratio in all tissues by > 50%, with strain- and tissue-specific differences in the effects of perindopril on the levels of individual angiotensin peptides. None of the changes in Ang II levels persisted after perindopril withdrawal. In contrast to those of Donryu rats, plasma angiotensinogen levels of perindopril-withdrawn SHR were 14% lower than those of vehicle-treated SHR (p = 0.0356). Although the lower BP of perindopril-withdrawn SHR was not associated with an alteration in Ang II levels, the suppressed plasma angiotensinogen levels may have contributed to the lower BP of these rats. Alternatively, another action of perindopril, such as a change in cardiovascular structure, may have been responsible for the reduced BP of perindopril-withdrawn SHR.

Effects of losartan on angiotensin and bradykinin peptides and angiotensin-converting enzyme.

Antagonists of the type 1 (AT1) angiotensin II (Ang II) receptor increase renin secretion and plasma Ang II levels, and the increased Ang II levels may counteract the effects of the antagonist. Moreover, other investigators have suggested that the reactive increase in Ang II levels may increase bradykinin (BK) levels through stimulation of the type 2 Ang II receptor (AT2). We investigated the acute effects of the AT1 receptor antagonist losartan (intraarterial injection of 10 mg/kg every 12 h) in male Sprague Dawley rats by measuring circulating angiotensin and BK peptides at 6, 12, and 24 h. Whereas acute losartan administration increased blood angiotensin levels four- to sixfold, blood BK levels were unchanged. We also investigated the effects of losartan administered for 8 days (10 mg/kg every 12 hours, by intraperitoneal injection) on circulating and tissue levels of angiotensin and BK peptides, and angiotensin-converting enzyme (ACE). Losartan increased plasma renin levels 100-fold; plasma angiotensinogen levels decreased to 24% of control; and plasma aldosterone levels were unchanged. Ang II levels in plasma, adrenal, lung, heart, and aorta were increased 25-, 8-, 3.5-, 2.4-, and 14-fold, respectively, by losartan administration. By contrast, kidney Ang II levels decreased to 71% of control, accompanied by a decrease in kidney levels of BK-(1-7) and BK-(1-9). No other tissue showed a change in BK peptide levels, except for a reduction in blood levels of BK-(1-8) to 43% of control. Plasma ACE increased by 13-50%, but tissue ACE levels were unchanged. These data demonstrate that losartan has tissue-specific effects on endogenous levels of angiotensin and BK peptides and indicate that increased BK levels do not contribute to the actions of losartan. The absence of a reactive increase in endogenous kidney levels of Ang II indicates that this tissue is likely to be the most sensitive to AT1 receptor antagonism.

Increased levels of bradykinin and its metabolites in tissues of young spontaneously hypertensive rats.

OBJECTIVE: To determine whether tissue kinin levels in spontaneously hypertensive rats (SHR) differ from those in normotensive rats. DESIGN AND METHODS: The tissue levels of bradykinin-(1-9) and its metabolites bradykinin-(1-7) and bradykinin-(1-8) were measured in kidney, and bradykinin-(1-9) and bradykinin-(1-7) were measured in adrenal, lung, heart, aorta, brown adipose tissue and brain of male SHR and the normotensive genetically homogeneous Donryu rat strain, at age 6, 10 and 20 weeks. RESULTS: In comparison with Donryu rats, bradykinin-(1-7), bradykinin-(1-8) and bradykinin-(1-9) levels were increased in kidney, and bradykinin-(1-7) and bradykinin-(1-9) levels were increased in adrenal, lung and heart of SHR aged 6 weeks. Bradykinin-(1-7) levels remained elevated in adrenal and lung of SHR aged 10 weeks. The bradykinin-(1-7): bradykinin-(1-9) ratio for kidneys of SHR was reduced at all ages and the bradykinin-(1-8):bradykinin-(1-9) ratio was reduced at age 10 and 20 weeks. Bradykinin peptide levels in aorta, brown adipose tissue and brain were similar for SHR and Donryu rats. CONCLUSION: The increased levels of bradykinin-(1-9) and its metabolites in kidney, adrenal, lung and heart tissues of young SHR suggest increased kallikrein activity in these tissues. Moreover, the reduced bradykinin-(1-7):bradykinin-(1-9) and bradykinin-(1-8):bradykinin-(1-9) ratios in kidneys of SHR indicate reduced endopeptidase- and carboxypeptidase-mediated metabolism of bradykinin-(1-9), which may have contributed to the increased bradykinin-(1-9) levels in this tissue. Together with the previously reported hypotensive effect of bradykinin-(1-9) antagonism in young SHR, and the cosegregation of the SHR kallikrein gene with blood pressure, the increased bradykinin-(1-9) levels in tissues of young SHR are consistent with a role for this peptide in the pathogenesis of hypertension in those rats.

Angiotensin and bradykinin peptides in the TGR(mRen-2)27 rat.

The transgenic TGR(mRen-2)27 rat, in which the Ren-2 mouse renin gene is transfected into the genome of the Sprague-Dawley rat, develops severe hypertension at a young age that responds to inhibitors of angiotensin-converting enzyme and to antagonists of the type 1 angiotensin II (Ang II) receptor. Despite this evidence that the hypertension is Ang II dependent, TGR(mRen-2)27 rats have suppressed renal renin and renin mRNA content, and there is controversy concerning the plasma levels of renin and Ang II in these rats. We investigated the effect of the transgene on circulating and tissue levels of angiotensin and bradykinin peptides in 6-week-old male homozygous TGR(mRen-2)27 rats. Systolic blood pressure of TGR(mRen-2)27 rats was 212 +/- 4 mm Hg (mean +/- SEM, n = 25) compared with 108 +/- 2 mm Hg (n = 29) for age- and sex-matched Sprague-Dawley rats. Compared with control rats, TGR(mRen-2)27 rats had increased plasma levels of active renin (4.5-fold), prorenin (300-fold), and Ang II (fourfold) as well as tissue levels of Ang II (twofold to fourfold in kidney, adrenal, heart, aorta, brown adipose tissue, and lung and 18-fold in brain). Plasma angiotensinogen levels were reduced to 73% of control, and plasma aldosterone levels were increased fourfold. Plasma angiotensin-converting enzyme was reduced to 64% of control. Compared with control rats, TGR(mRen-2)27 rats had increased bradykinin levels in brown adipose tissue (1.9-fold) and lung (1.6-fold).(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin peptides in spontaneously hypertensive and normotensive Donryu rats.

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)

Effects of converting enzyme inhibitors on angiotensin and bradykinin peptides.

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-(1-9) levels approximately eightfold, with a threshold dose of 0.052 mg/kg per day, and increased bradykinin-(1-9) levels in kidney, heart, and lung in parallel with the changes observed for plasma. By contrast, aortic and brown adipose tissue bradykinin-(1-9) and bradykinin-(1-7) levels increased severalfold for perindopril doses as low as 0.006 mg/kg per day. Lisinopril also increased aortic bradykinin-(1-9) and bradykinin-(1-7) levels at doses below the threshold for the decrease in the ratio of Ang II to Ang I. These data indicate that renal Ang II levels and vascular bradykinin-(1-9) levels respond to low doses of converting enzyme inhibitor and may be important mediators of the effects of these compounds. The parallel increases in bradykinin-(1-9) and bradykinin-(1-7) levels in aorta and brown adipose tissue, at inhibitor doses below the threshold for inhibition of Ang I conversion, may result from a mechanism different from inhibition of "classic" angiotensin-converting enzyme.

Nephrectomy, converting enzyme inhibition, and angiotensin 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)-(1-7), Ang II, Ang-(1-9), 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-renin-like enzyme.

Sheep hypothalamus contains a non-angiotensin ligand for type 1 and type 2 angiotensin II receptors.

1. The aim of this study was to determine whether the brain contains an alternative ligand for angiotensin II (AII) receptors. 2. A radioreceptor assay based upon bovine cerebellar membranes (Type 2 AII receptors) was used to monitor the partial purification of an AII-like material from sheep hypothalami. 3. This material displaces 125I-[Sar1, Ala8]-AII from both type 1 (rat adrenal capsular membranes) and Type 2 AII receptors in a manner parallel to that of AII. It has a size of approximately 30,000 Da, is strongly cationic, is stable to boiling but is destroyed by trypsin. It is not recognized by AII antisera. 4. These data provide direct evidence for a non-angiotensin endogenous ligand for brain AII receptors. This novel ligand may play a role in the regulation of blood pressure and other actions mediated by brain AII receptors.

Bradykinin peptides in kidney, blood, and other tissues of the rat.

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-(1-7), bradykinin-(1-8), and bradykinin-(1-9). Together with a carboxy terminal-directed radioimmunoassay, we characterized bradykinin peptides in rat kidney and blood. The predominant bradykinin peptides in kidney were bradykinin-(1-9) (approximately 100 fmol/g wet weight of tissue) and bradykinin-(1-7) (approximately 70 fmol/g), with low levels of bradykinin-(1-8) (approximately 8 fmol/g) and bradykinin-(4-9) (approximately 12 fmol/g) detectable; bradykinin-(2-9) and bradykinin-(3-9) were below the limits of detection. In blood, the levels of bradykinin-(1-9) were very low (approximately 2 fmol/ml), and other bradykinin peptides were below the limits of detection. Ile,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-(1-8) and bradykinin-(1-9) and a decrease in the bradykinin-(1-7)/bradykinin-(1-9) ratio. The amino terminal-directed radioimmunoassay was also applied to heart, aorta, brown adipose tissue, adrenal lung, and brain. For these tissues, bradykinin-(1-7) and bradykinin-(1-9) were of similar abundance (16-340 fmol/g), with lower levels of bradykinin-(1-8). 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-(1-9) is the predominant bioactive peptide in all tissues, and a major pathway of bradykinin-(1-9) metabolism involves the formation of bradykinin-(1-7). In kidney, angiotensin converting enzyme plays an important role in bradykinin-(1-9) metabolism, and increased bradykinin-(1-9) and bradykinin-(1-8) levels may mediate in part the renal effects of converting enzyme inhibition.

Differential regulation of angiotensin peptide levels in plasma and kidney of the rat.

We compared the effects of the converting enzyme inhibitor perindopril on components of the renin-angiotensin system in plasma and kidney of male Sprague-Dawley rats administered perindopril in their drinking water at two doses (1.4 and 4.2 mg/kg) over 7 days. Eight angiotensin peptides were measured in plasma and kidney: angiotensin-(1-7), angiotensin II, angiotensin-(1-9), angiotensin I, angiotensin-(2-7), angiotensin III, angiotensin-(2-9), and angiotensin-(2-10). In addition, angiotensin converting enzyme activity, renin, and angiotensinogen were measured in plasma, and renin, angiotensinogen, and their respective messenger RNAs were measured in kidney; angiotensinogen messenger RNA was also measured in liver. In plasma, the highest dose of perindopril reduced angiotensin converting enzyme activity to 11% of control, increased renin 200-fold, reduced angiotensinogen to 11% of control, increased angiotensin-(1-7), angiotensin I, angiotensin-(2-7), and angiotensin-(2-10) levels 25-, 9-, 10-, and 13-fold, respectively; angiotensin II levels were not significantly different from control. By contrast, for the kidney, angiotensin-(1-7), angiotensin I, angiotensin-(2-7), and angiotensin-(2-10) levels did not increase; angiotensin II levels fell to 14% of control, and angiotensinogen fell to 12% of control. Kidney renin messenger RNA levels increased 12-fold, but renal renin content and angiotensinogen messenger RNA levels in kidney and liver were not influenced by perindopril treatment. These results demonstrate a differential regulation of angiotensin peptides in plasma and kidney and provide direct support for the proposal that the cardiovascular effects of converting enzyme inhibitors depend on modulation of tissue angiotensin systems. Moreover, the failure of kidney angiotensin I levels to increase with perindopril treatment, taken together with the fall in kidney angiotensinogen levels, suggests that angiotensinogen may be a major rate-limiting determinant of angiotensin peptide levels in the kidney.