Effects of empagliflozin on blood pressure and markers of arterial stiffness and vascular resistance in patients with type 2 diabetes.

AIMS: To determine the effects of empagliflozin on blood pressure (BP) and markers of arterial stiffness and vascular resistance in patients with type 2 diabetes mellitus (T2DM). METHODS: We conducted a post hoc analysis of data from a phase III trial in patients with T2DM and hypertension receiving 12 weeks' empagliflozin and four phase III trials in patients with T2DM receiving 24 weeks' empagliflozin (cohort 1, n = 823; cohort 2, n = 2477). BP was measured using 24-h BP monitoring (cohort 1) or seated office measurements (cohort 2). RESULTS: Empagliflozin reduced systolic BP (SBP) and diastolic BP in both cohorts (p < 0.001 vs placebo), without increasing heart rate. Empagliflozin reduced pulse pressure (PP; adjusted mean difference vs placebo cohort 1: -2.3 mmHg; cohort 2: -2.3 mmHg), mean arterial pressure (MAP; cohort 1, -2.3 mmHg; cohort 2, -2.1 mmHg) and double product (cohort 1, -385 mmHg × bpm; cohort 2, -369 mmHg × bpm) all p < 0.001 vs placebo. There was a trend towards a reduction in the ambulatory arterial stiffness index (AASI) with empagliflozin in cohort 1 (p = 0.059 vs placebo). AASI was not measured in cohort 2. Subgroup analyses showed that there were greater reductions in PP with increasing baseline SBP in cohort 1 (p = 0.092). In cohort 2, greater reductions in MAP were achieved in patients with higher baseline SBP (p = 0.027) and greater reductions in PP were observed in older patients (p = 0.011). CONCLUSIONS: Empagliflozin reduced BP and had favourable effects on markers of arterial stiffness and vascular resistance.

Estimated glomerular filtration rate (eGFR) as a predictor of outcome after infrainguinal bypass in patients with critical limb ischemia.

OBJECTIVES: Renal insufficiency is a risk factor for poor outcome after infrainguinal bypass in patients with critical limb ischemia (CLI). Estimated glomerular filtration rate (eGFR) takes age, gender and body size into account and therefore represents actual renal function more accurately than serum creatinine level alone. The aim of this study was to determine the impact of different stages of renal insufficiency on outcome and to assess the prognostic significance of eGFR in patients with CLI. MATERIAL AND METHODS: 603 patients with CLI who underwent infrainguinal bypass between January 2002 and December 2005 at our institution were included in this retrospective study. We estimated GFR using the Modification of Diet in Renal Disease (MDRD) Study equation. Survival, leg salvage and amputation-free survival were calculated using Kaplan-Meier method. Cox regression analysis was performed to calculate hazard ratios for different outcome variables. RESULTS: Adjusted hazard ratio (HR) of mortality, limb loss and limb loss and/or death for eGFR < 30 ml/min/1.73 m(2) versus serum creatinine > 200 micromol/l was 4.0 (95% CI 2.22-7.39) vs 3.5 (95% CI 1.82-6.84), 6.5 (95% CI 2.71-15.59) vs 6.2 (95% CI 2.47-15.56) and 4.0 (95% CI 2.40-6.63) vs 3.6 (95% CI 2.03-6.25), respectively. CONCLUSION: Estimated GFR is better predictor of survival, leg salvage and amputation-free survival than serum creatinine alone. eGFR < 30 ml/min/1.73 m(2) is independent risk factor for all three outcome endpoints.

No effect of short term angiotensin II infusion on plasma renin substrate levels in man.

We studied the effect of angiotensin II (A-II) infusion (4 ng/kg BW.min) on plasma renin substrate (RS) levels and PRA in five normal men during normal, diuretic-stimulated, and enalapril-interrupted function of the renin-angiotensin system. A-II infusion increased (15-25%) both systolic and diastolic blood pressure in the normal state and during angiotensin-converting enzyme inhibition, whereas the increase during diuretic-stimulated renin-angiotensin system function was less. The plasma RS concentration was measured by both direct and indirect RIA. The mean basal plasma RS levels, measured with direct assay, were 1516 +/- 150 (SE) in the normal state, 1566 +/- 150 after diuretic administration, and 1650 +/- 133 nmol/L after enalapril administration. The corresponding mean basal plasma RS levels measured with the indirect assay were 1073 +/- 100, 1031 +/- 57, and 902 +/- 78 nmol/L, respectively. Plasma RS levels did not change during or after the A-II infusions, whereas PRA decreased significantly in all experimental conditions. The results suggest that A-II exerts no direct stimulatory effect on hepatic release of RS. Thus, A-II appears not to be important in the short term regulation of plasma RS levels.

Polymorphism of the glycogen synthase gene in hypertensive and normotensive subjects.

Hypertension and non-insulin-dependent diabetes mellitus (NIDDM) are characterized by a strong genetic component and impaired ability to store glucose as glycogen in skeletal muscle. Impaired insulin activation and altered genetic control of muscle glycogen synthase, the rate-limiting enzyme for glucose storage in skeletal muscle, could provide an explanation for this insulin resistance. We examined whether there is an association between the glycogen synthase gene (Xba I polymorphism) and hypertension in 304 nondiabetic subjects. We examined glucose tolerance with an oral glucose tolerance test and glucose storage in skeletal muscle with the euglycemic insulin clamp technique in combination with indirect calorimetry. The Xba I A2 allele of the glycogen synthase gene was enriched in subjects with hypertension and a family history of NIDDM (48%) compared with normotensive subjects without a family history of NIDDM (6%, P < .0001). The presence of the A2 versus the A1 allele was associated with decreased rates of insulin-stimulated glucose storage in hypertensive subjects (11.2 +/- 2.3 versus 16.9 +/- 2.6 mumol/kg lean body mass per minute, P = .029) but not in normotensive subjects (28.0 +/- 4.6 versus 29.6 +/- 3.7 mumol/kg lean body mass per minute). In conclusion, Xba I polymorphism of the glycogen synthase gene identifies a subgroup of hypertensive subjects with a family history of NIDDM. The data suggest that a locus in the glycogen synthase gene region on chromosome 19 may serve as a "thrifty gene," increasing susceptibility for insulin resistance when exposed to other environmental or genetic factors.

Dual inhibition of neutral endopeptidase and angiotensin-converting enzyme in rats with hypertension and diabetes mellitus.

It has been suggested that combined inhibition of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) may lower blood pressure more effectively than either treatment alone, independent of the degree of salt and volume status or the activity of the renin-angiotensin system. The effects of NEP inhibition in hypertension associated with diabetes mellitus are largely unknown. We therefore compared ACE inhibition, NEP inhibition, and dual NEP/ACE inhibition in diabetic hypertensive rats. Spontaneously hypertensive rats (SHR) aged 9 to 10 weeks were injected with either streptozotocin (45 mg/kg) or citrate buffer and randomized to receive either the ACE inhibitor captopril (25 mg/kg BID), the NEP inhibitor SCH 42495 (30 mg/kg BID), the dual NEP/ACE inhibitor S 21402 (25 or 50 mg/kg BID), or vehicle by gavage for 4 weeks. A group of diabetic SHR was also allocated to receive the combination of SCH 42495 (30 mg/kg BID) and captopril (25 mg/kg BID). The degree of renal NEP inhibition was determined by autoradiography, and plasma renin activity (PRA) was determined by radioimmunoassay. In diabetic SHR, the dual NEP/ACE inhibitor (50 mg/kg BID), as well as the combination of the NEP inhibitor and the ACE inhibitor, reduced systolic blood pressure more effectively than the ACE inhibitor (P<0.001) or the NEP inhibitor (P<0.001) alone. In nondiabetic SHR, the dual NEP/ACE inhibitor and the ACE inhibitor were equally effective, while the NEP inhibitor had only slight blood pressure lowering effects. Relative heart weight decreased in parallel to the changes in blood pressure. Renal NEP was clearly inhibited (70% to 92%; P<0.001) by both the NEP inhibitor and the dual NEP/ACE inhibitor. Both the ACE inhibitor and the dual NEP/ACE inhibitor increased PRA, but the stimulating effect of dual NEP/ACE inhibition on PRA was less than that observed with ACE inhibition alone (P<0.05). Albuminuria in diabetic SHR was lower during treatment with both the dual NEP/ACE inhibitor (50 mg/kg BID) and the combination of NEP inhibition and ACE inhibition compared with vehicle treatment (P<0.05). In conclusion, the present study shows that hypertension in SHR with streptozotocin-induced diabetes is modulated by natriuretic peptides and thus is sensitive to NEP inhibition. The increased efficacy of dual NEP/ACE inhibition on blood pressure in diabetic SHR, compared with ACE or NEP inhibition alone, suggests that this therapeutic approach may prove beneficial in the treatment of hypertension associated with diabetes mellitus and other forms of volume-dependent hypertension.

Comparison of the angiotensin II antagonist losartan with the angiotensin converting enzyme inhibitor enalapril in patients with essential hypertension.

OBJECTIVE: To evaluate the blood pressure lowering efficacy as well as tolerability and safety of the angiotensin II antagonist losartan compared with that of the angiotensin converting enzyme inhibitor enalapril in patients with mild-to-moderate essential hypertension. DESIGN AND METHODS: The study was a multicentre, double-blind, double-dummy, randomized, parallel study. Patients (n = 407) with diastolic blood pressure > or = 95 and < or = 120 mmHg at the end of a 2-week baseline placebo period were randomly allocated to receive either 50 mg losartan once a day or 20 mg enalapril once a day for 12 weeks. Blood pressure, clinical and laboratory safety, specific symptoms including coughing determined using a symptoms questionnaire and metabolic variables were examined at baseline and at weeks 6 and 12. RESULTS: Both losartan and enalapril decreased systolic and diastolic blood pressure from baseline at weeks 6 and 12. Blood pressure changes from baseline at trough (22-26 h after the dose) did not differ between the two groups in the per-protocol analysis. Response to treatment at trough was excellent or good (diastolic blood pressure < 90 mmHg or reduction in diastolic blood pressure of 10 mmHg) in 51 and 53% of the patients in the losartan and enalapril groups, respectively. Enalapril administration increased dry coughing symptoms whereas losartan did not. The incidence of dry coughing was 1.0 and 12.2% as a spontaneously reported discomfort at week 12 and 3.0 and 15.1% as a clinical adverse experience in the losartan and enalapril groups, respectively. The difference from baseline at week 12 in the incidence of dry coughing between the two groups was 14.9% as a specific symptom in the symptoms questionnaire. Losartan reduced serum uric acid concentration, whereas effects on other metabolic parameters did not differ between the groups. CONCLUSIONS: Losartan is an effective and well-tolerated antihypertensive drug showing similar blood-pressure-lowering efficacy to that of enalapril at trough. However, in contrast to enalapril, losartan does not increase the incidence of dry coughing. Thus, the angiotensin II antagonist losartan provides a promising new approach to treatment of hypertension.

Screening for renovascular hypertension in a population with relatively low prevalence.

OBJECTIVE: To evaluate the accuracy and cost-efficacy of the diagnostic procedure and treatment for renovascular hypertension. SETTING AND PATIENTS: A total of 519 patients referred to the university clinic for hypertension were screened for renovascular hypertension with 405 captopril challenge tests (CCT) and 450 captopril renographies (CRG). INTERVENTIONS: Abdominal angiography was performed on 84 patients for positive screening. Fifteen patients underwent angiography for a sole suspicious clinical presentation. The angiography revealed 17 renal artery stenoses and five occlusions in 20 patients. Fifteen technically successful angioplasties and three nephrectomies were performed. RESULTS: In the patients who underwent angiography, CCT had a specificity of 39% and a sensitivity of 67% for renovascular hypertension. CRG had a sensitivity of 100% and a specificity of 68%. In the whole study population, the estimated specificity of CCT was 88% and that of CRG 95%. Invasive treatment reduced systolic/diastolic blood pressure from 157/99 to 140/87 mmHg and the number of antihypertensive drugs used from 2.6 to 1.4 in 16 patients (mean age 49 years). Angiotensin converting enzyme (ACE) inhibition was effective in four elderly patients. Cost-efficacy analysis Screening with CRG and invasive treatment cost US$15400 per successful invasive treatment Equally effective pharmacological treatment would have cost US$10400. Limiting the screening with CRG to the 173 patients with no obvious renal parenchymal disease and with hypertension at a younger age (< or =30 years) or unresponsive to two antihypertensive drugs (diastolic blood pressure > 90 mmHg) would have yielded a prevalence of 12% and missed only one elderly patient who responded to ACE inhibition. The limited screening, along with invasive treatment, would have cost US$7300 per patient CONCLUSIONS: CRG is superior to CCT for screening of renovascular hypertension. Screening with CRG is cost-effective when limited to patients with no obvious renal parenchymal disease and with hypertension that does not respond to two antihypertensive drugs or is detected in patients no older than 30 years.

Atrial natriuretic peptide in congestive heart failure.

Release of atrial natriuretic peptide (ANP) appears to be a compensatory response in congestive heart failure (CHF) that may counterbalance the adverse effects of stimulated renin-angiotensin and sympathetic nervous systems. We observed increased plasma ANP concentrations in CHF patients in New York Heart Association functional classes II to IV. The fact that such responses already become evident when a patient is in New York Heart Association class II supports the concept that ANP release may counteract the detrimental effects of stimulation of renin and the sympathetic nervous system even in the early phases of heart failure by promoting diuresis and natriuresis, as well as vasodilatation, thus reducing both pre- and afterload. When CHF is severe, however, the counterbalancing effects of ANP may be offset by vasoconstriction and fluid and sodium retention.

Induction of angiotensin I-converting enzyme in rat lung with captopril: the effect of adrenalectomy.

In spontaneously hypertensive rats, treatment with captopril, 0.2 g/liter of drinking fluid for 12 to 24 weeks, caused a threefold increase in serum angiotensin I-converting enzyme activity. Angiotensin I-converting enzyme increased 25 to 120 percent in lung plasma membranes. The elution profile of angiotensin I-converting enzyme on DEAE cellulose and after gel filtration on Sepharose 4B was unchanged by captopril. The Km value value also remained unchanged. In Wistar rats subjected to bilateral adrenalectomy, treatment with the same dose of captopril for 3 days resulted in increased serum angiotensin I-converting enzyme activity in both sham-operated and adrenalectomized rats, but angiotensin I-converting enzyme concentration increased in lung plasma membranes from sham-operated rats and captopril-treated rats only. We conclude that captopril causes induction of angiotensin-converting enzyme biosynthesis in spontaneously hypertensive and Wistar rats. The change is a quantitative one. Intact adrenal glands may be important for the incorporation of angiotensin I-converting enzyme into lung membranes.

Renal and vascular effects of atrial natriuretic factor during cardiopulmonary bypass.

STUDY OBJECTIVE: To evaluate renal and vasodilator effects of synthetic atrial natriuretic factor (ANF) in patients undergoing cardiopulmonary bypass (CPB) with special reference to the applicability of ANF as a diuretic and natriuretic. DESIGN: The study consisted of two parts. The first 15 consecutive patients in a university hospital received a pharmacologically effective bolus dose of 100 micrograms ANF, as demonstrated previously in other studies, or placebo. After analysis of the bolus data (see "Results" section below), the 12 subsequent patients were administered ANF 50 micrograms as a constant 30-min infusion at a rate of 1.67 micrograms/min or placebo. PATIENTS: The patients were scheduled for elective coronary artery bypass grafting operation. There was no evidence of congestive heart failure in any patient, and no one had an endocrine or renal disorder. INTERVENTIONS: After achievement of hypothermia (29 to 30 degrees C of rectal temperature) during CPB, a bolus dose of ANF 100 micrograms was given or an infusion of ANF 1.67 micrograms/min for 30 min, ie, a total dose of 50 micrograms was started. The control patients received placebo correspondingly. Intravenous fluids were administered according to a predetermined scheme. MEASUREMENTS AND MAIN RESULTS: For the pharmacologic effects of ANF urine volume, urinary sodium excretion and mean arterial pressure (MAP) were measured. Only three of the eight patients receiving the bolus dose of ANF had a diuretic and natriuretic response to the drug, and the responses were significantly related (r = 0.91, p less than 0.05 and r = 0.98, p less than 0.001, respectively) to the prevailing MAP at the time of the bolus administration. The bolus dose of ANF decreased MAP significantly (p less than 0.001 vs placebo) from 65 +/- 6 (mean +/- SEM) to 55 +/- 6 mm Hg within 5 min. The infusion of ANF did not affect MAP, but it increased urine output (16.1 +/- 5.0 ml/min, when the data obtained during the 30-min infusion and a 30-min period after the infusion were combined) and urinary sodium excretion (1,651 +/- 514 microEq/min) significantly (p less than 0.05 and p less than 0.01, respectively) as compared with the corresponding values of 3.3 +/- 1.1 ml/min and 386 +/- 141 microEq/min after placebo. CONCLUSIONS: Prevailing arterial pressure is an important determinant of the diuretic and natriuretic activity of synthetic ANF in patients undergoing CPB. A low-dose infusion of ANF (50 micrograms within 30 min) provides diuresis and natriuresis without significant changes in MAP in these patients.

Plasma and pericardial fluid natriuretic peptide levels in postinfarction ventricular dysfunction.

AIMS: In the present study we examined plasma and pericardial fluid ANP and BNP concentrations in postinfarction ventricular dysfunction. The association of peptide levels to left ventricular (LV) dysfunction and to the localization of the myocardial infarction (MI) was studied. METHODS AND RESULTS: Plasma and pericardial fluid samples were obtained from 37 patients undergoing coronary bypass surgery. According to the ECG and preceding coronary angiography, the patients were divided into three groups: previous anterior myocardial infarction (MI) (n=12), previous inferior/posterior MI (n=15) and no history of MI (n=10). When compared to the control group with no MI, the patients with anterior MI had elevated plasma ANP and BNP (134+/-13 vs. 81+/-15 pg/ml, P<0.01 and 95+/-10 pg/ml vs. 26+/-8 pg/ml, P<0.01, respectively) and pericardial fluid BNP (473+/-60 pg/ml vs. 57+/-8 pg/ml, P<0.001) levels. The plasma natriuretic peptide concentrations were not increased in the patients with inferior/posterior MI, but the pericardial fluid BNP concentrations were greater than in the patients with no history of MI (129+/-35 pg/ml vs. 57+/-8 pg/ml, P<0.05). Six of the 12 patients with previous anterior MI had LVEF> or =45%. Despite their normal LV systolic function, these patients had increased plasma and pericardial fluid BNP levels when compared to the group with no history of MI (68+/-18 pg/ml vs. 26+/-8 pg/ml, P<0.05 and 534+/-258 pg/ml vs. 57+/-8 pg/ml, P<0.01, respectively). CONCLUSIONS: Previous anterior myocardial infarction was associated with increased cardiac BNP production even if the LV systolic function was normal (LVEF> or =45%). The high pericardial fluid BNP concentrations in postinfarction patients suggest that the BNP synthesis and release are augmented in the ventricular myocardium independent from the LVEF.

Comparison of renin-angiotensin to calcium channel blockade in renal disease.

Whether any class of antihypertensive drugs has specific renoprotective effects above and beyond lowering of blood pressure is still debatable. The renin-angiotensin system (RAS) is both localized and has many actions within the kidney, on intrarenal hemodynamics, on the mesangial cell, as well as stimulating growth factors and cytokines. Angiotensin converting enzyme (ACE) inhibitors have been shown to ameliorate the progression of renal failure. How much of this beneficial effect is due to their hemodynamic effects, how much to non-hemodynamic effects and how much to their effects on bradykinin and other putative ACE substrates is still unclear. Experimentally it can be shown that inhibiting ACE but preventing the fall in systemic blood pressure by salt loading abolishes renoprotection. Bradykinin has been implicated in both the beneficial and the adverse effects of ACE inhibitors. Because of this and because ACE inhibitors may not provide complete blockade of the RAS, angiotensin receptor (AT1R) antagonists have been developed. Experimentally AT1R antagonists have been shown to reproduce most of the beneficial effects of ACE inhibitors. The experience in humans is more limited but they have been demonstrated to be efficacious in hypertension, to reduce proteinuria, and produce a favorable hemodynamic effect in congestive cardiac failure with a low incidence of adverse effects and without cough. Calcium channel blockers (CCB) also have additional properties that may provide renoprotection beyond lowering blood pressure. However, as the different types of CCB block different calcium channels their effects may differ substantially. The inconsistency of the data in the renoprotective effect of CCB may reflect these differences. Quantitatively probably the most important factor in preventing the progress of renal failure by antihypertensive drugs is strict control of blood pressure. Lowering blood pressure by drugs is most likely effective by both reducing physical and sheer stress damage, as well as turning off the signal for the activation and production of vasoactive peptides and cytokines.

Atrial pressure and hormonal and renal responses to acute cardiac tamponade.

The effect of acute cardiac tamponade on atrial pressures, plasma atrial natriuretic factor concentration and renin activity, and renal water and electrolyte excretion was studied in pigs loaded intravenously with hydroxyethyl starch and maintained on a continuous intravenous infusion of isotonic saline solution. Saline solution was infused into the pericardial space in 6 anesthetized pigs until a predetermined decrease of 20% in mean arterial pressure was achieved. Another 6 sham-treated pigs served as controls. Tamponade increased atrial intracavitary pressures but decreased atrial transmural (distending) pressures. These changes in atrial pressures were reversed after release of tamponade. Changes in plasma atrial natriuretic factor concentration correlated positively with changes in atrial transmural pressures. Tamponade increased plasma renin activity and decreased urine flow and renal sodium and potassium excretion, and release of tamponade reversed these changes. Thus, the tamponade-induced reduction in atrial distention is associated with hormonal changes, which may contribute to the reductions in diuresis and natriuresis observed in this connection.

Inhibition of either angiotensin-converting enzyme or neutral endopeptidase induces both enzymes.

Synthesis of angiotensin-converting enzyme is induced during its chronic inhibition. Like angiotensin-converting enzyme, neutral endopeptidase (EC 3.4.24.11) is a plasma membrane peptidase. We studied changes of the two enzymes in lung, kidney and serum in a coronary ligation model of experimental congestive heart failure, and during chronic inhibition of the enzymes. Coronary-ligated rats (n = 19) and sham-operated controls (n = 18) were given SCH 34826 [(S)-N-[N-[1-[[(2,2-dimethyl-1,3-dioxolan-4-yl) methoxy]carbonyl]-2-phenylethyl]-L-phenylalanine]-beta-alanine], a specific neutral endopeptidase inhibitor (n = 13), captopril (n = 12), or vehicle (n = 12) for 4 days, and exsanguinated. Pulmonary angiotensin-converting enzyme was induced both by captopril (52% compared to vehicle) and by SCH 34826 (21%). Serum angiotensin-converting enzyme was induced by captopril (44%). Neutral endopeptidase was induced in lung by captopril (73%), and in kidney by SCH 38426 (32%). Compared to controls, the relative heart weight of rats with heart failure was increased by 29%, and the plasma level of atrial natriuretic peptide elevated by 74%, but enzyme activities were not different. We conclude that, in the rat, separate inhibition of either angiotensin-converting enzyme or neutral endopeptidase induces both enzymes, and that the induction varies in different tissues. Alterations in the substrates of the two enzymes, e.g. in bradykinin, might cause these changes.

Efficacy of captopril in experimental low renin hypertension.

Captopril (SQ 14225) had a clear antihypertensive effect in rat Heymann nephritis-DOCA-NaCl hypertension, a low renin model introduced recently, but was ineffective in 1-kidney-DOCA-NaCl hypertension although plasma renin activity (PRA) was suppressed similarly in both. Thus, the antihypertensive effect of captopril was independent of circulating renin. This result also suggests different pathogenetic mechanisms of hypertension in these two DOCA-NaCl models.

Induction of angiotensin I-converting enzyme rat lung with Captopril (SQ 14225).

Angiotensin I-converting enzyme (ACE, EC 2.4.15.1.) was measured in serum and in pulmonary plasma membranes of 40 spontaneously hypertensive rats (SHR, Okamoto Aoki strain), divided into 4 groups, and treated with SQ 14225 (Captopril), 0.2 mg . ml-1 in drinking water, for 0-24 weeks. Serum ACE activity increased 2.5-3 fold after 12-24 weeks of SQ 14225 treatment, paralleled by an increase of ACE concentration in purified pulmonary plasma membranes (25-52%), and in ACE concentration upon solubilization with Triton X-100 from such plasma membranes (96-120%). We conclude that the ACE inhibitor, SQ 14225, causes marked induction of pulmonary ACE biosynthesis. High serum ACE activity probably reflects increased total biosynthesis of the enzyme.

Induction of angiotensin-converting enzyme with the ACE inhibitory compound MK-421 in rat lung.

Having observed that treatment of rats with captopril led to an increased ACE activity in serum and ACE concentration in lungs, we treated female Wistar Kyoto rats for 7 days with the esterified ACE inhibitor, MK-421 (1.0 mg/kg body weight per day), administered by Alzet osmotic minipump. Serum ACE activity decreased by 67% during MK-421 treatment when measured in non-dialyzed serum samples. Removal of the drug by dialysis unmasked a 280% increase of serum ACE activity. ACE concentration of crude lung homogenate increased 134% in MK-421-treated rats and ACE concentration in purified pulmonary plasma membranes increased by 34%. The increase of serum and lung ACE in MK-421-treated rats was similar to that seen in rats treated with captopril, and was probably due to induction of ACE biosynthesis. The mechanisms of this induction are unknown.

Haemodynamic effects of atrial natriuretic peptide in rats with heart failure.

Plasma atrial natriuretic peptide (ANP), a hormone secreted by the heart, is elevated in cardiac failure. In the aim to study the role of ANP in cardiac failure, the haemodynamic response to ANP was examined in rats with chronic heart failure produced by coronary artery ligation. Plasma ANP was clearly elevated in all infarcted rats before ANP injection as compared with controls. ANP lowered the blood pressure and impaired cardiac contractility, as measured by the maximal positive value of the first derivative of the pressure signal, in a dose-dependent manner. The blood pressure lowering effects of ANP were attenuated in rats with cardiac failure. We conclude that rats with experimentally induced heart infarct are partially resistant to the haemodynamic effects of ANP.

Prolonged neutral endopeptidase inhibition in heart failure.

We studied the hormonal, renal and hemodynamic effects of prolonged treatment with SCH 39370, a new neutral endopeptidase (NEP) inhibitor, in experimental congestive heart failure (CHF). Coronary-ligated CHF rats and sham-operated controls received vehicle or SCH 39370 30 mg/kg s.c. twice daily for six days. In rats with heart failure, SCH 39370 elevated the high plasma atrial natriuretic peptide (ANP) and cyclic guanosine monophosphate (cGMP) levels 2-fold both initially and at the end of the experiment. Initially, water balance was more negative in SCH 39370-treated CHF rats than in those treated with vehicle. In all SCH 39370-treated rats, ANP, cGMP and electrolyte excretion and diuresis were pronounced for 6 h after injection but attenuated thereafter. Blood pressure and pulse remained unchanged. On reverse phase high performance liquid chromatography (HPLC), ANP-(99-126) appeared to be the only circulating form of ANP in rats with heart failure. Three forms have been discovered in patients with heart failure. HPLC revealed only intact ANP in plasma of rats with heart failure during SCH 39370 treatment. NEP inhibitors may provide a new tool for treating chronic heart failure.

Competitive inhibitor binding assay (CIBA) of captopril and other ACE inhibitors.

We describe a new principle for measuring concentrations of pharmacologically active captopril or other angiotensin-converting enzyme (ACE) inhibitors in blood. Serum is incubated with 125I-labelled ACE inhibitor (351A, a p-hydroxy-benzamidine derivative of N-(1-carboxy-3-phenylpropyl)-L-lysyl-L-proline) in a nonequilibrated system, in which label and ACE inhibitor compete for binding to added serum ACE. Free label is separated by adsorption to coated charcoal. Sensitivity for captopril is 2 ng/ml, and for other tested ACE inhibitors 0.25-5 ng/ml. Results in healthy volunteers showed rapid absorption of captopril with maximal concentration of active drug within 1 h, and fast disappearance within 2.5 h. Stability of captopril was improved by immediate 1:100 dilution of blood samples with assay buffer. In spite of this precaution, analysis should be performed within two days to avoid loss of active drug due to polymerization and protein binding. Samples of other tested ACE inhibitors can be frozen and later analyzed at convenience. The new principle is simple, sensitive, and specific.