Dissociation of the prostaglandin and renin angiotensin systems during captopril therapy for chronic congestive heart failure secondary to coronary artery disease

Exercise and Organ Cross Talk

Chronic heart failure, diabetes, depression, and other chronic diseases are associated with high mortality rate and low cure rate. Exercise induces muscle contraction and secretes multiple myokines, which affects the signaling pathways in skeletal muscle tissues and regulate remote organ functions. Exercise is known to be effective in treating a variety of chronic diseases. Here we summarize how exercise influences skeletal muscle, heart, brain, gut, and liver, and prevents heart failure, cognitive dysfunction, obesity, fatty liver, and other diseases. Exercise training may achieve additional benefits as compared to the present medication for these chronic diseases through cross talk among skeletal muscle and other organs.

Cytokines, angiogenic, and antiangiogenic factors and bioactive lipids in preeclampsia

Preeclampsia is a low-grade systemic inflammatory condition in which oxidative stress and endothelial dysfunction occurs. Plasma levels of soluble receptor for vascular endothelial growth factor (VEGFR)-1, also known as sFlt1 (soluble fms-like tyrosine kinase 1), an antiangiogenic factor have been reported to be elevated in preeclampsia. It was reported that pregnant mice deficient in catechol-O-methyltransferase (COMT) activity show a preeclampsia-like phenotype due to a deficiency or absence of 2-methoxyoestradiol (2-ME), a natural metabolite of estradiol that is elevated during the third trimester of normal human pregnancy. Additionally, autoantibodies (AT1-AAs) that bind and activate the angiotensin II receptor type 1 a (AT1 receptor) also have a role in preeclampsia. None of these abnormalities are consistently seen in all the patients with preeclampsia and some of them are not specific to pregnancy. Preeclampsia could occur due to an imbalance between pro- and antiangiogenic factors. VEGF, an angiogenic factor, is necessary for the transport of polyunsaturated fatty acids (PUFAs) to endothelial cells. Hence reduced VEGF levels decrease the availability of PUFAs to endothelial cells. This leads to a decrease in the formation of anti-inflammatory and angiogenic factors: lipoxins, resolvins, protectins, and maresins from PUFAs. Lipoxins, resolvins, protectins, maresins, and PUFAs suppress insulin resistance; activation of leukocytes, platelets, and macrophages; production of interleukin-6 and tumor necrosis factor-α; and oxidative stress and endothelial dysfunction; and enhance production of prostacyclin and nitric oxide (NO). Estrogen enhances the formation of lipoxin A4 and NO. PUFAs also augment the production of NO and inhibit the activity of angiotensin-converting enzyme and antagonize the actions of angiotensin II. Thus, PUFAs can prevent activation of angiotensin II receptor type 1 a (AT1 receptor). Patients with preeclampsia have decreased plasma phospholipid concentrations of arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), the precursors of lipoxins (from AA), resolvins (from EPA and DHA), and protectins (from DHA) and prostaglandin E1 (PGE1 from DGLA: dihomo-γ-linolenic acid) and prostacyclin (PGI2 derived from AA). Based on these evidences, it is proposed that preeclampsia may occur due to deficiency of PUFAs and their anti-inflammatory products: lipoxins, resolvins, protectins, and maresins.

Controversies in heart failure. Are beneficial effects of angiotensin-converting enzyme inhibitors attenuated by aspirin in patients with heart failure?

To whatever extent the improvement in symptoms and survival rendered by treatment with ACE inhibitors is attributable to their effects on the circulation and the kidneys, this benefit can be rescinded by concomitant administration of aspirin. Although some useful prostaglandin-independent actions may persist, shutting down the entire prostaglandin system and trading off a substantial portion of the potential risk reduction with forfeit of salutary hemodynamic and renal effects is a high price to pay just to suppress production of TXA2. In patients requiring treatment for heart failure, if possible, aspirin should be avoided and the integrity of prostaglandin metabolism respected; the severer the heart failure the more compelling. There are other ways to inhibit platelet aggregation, some equally effective or even better than aspirin. Orally active platelet glycoprotein IIb/IIIa receptor antagonists, which may be more efficient than aspirin, have been developed and are now in clinical testing. Ticlopidine and clopidogrel, although more expensive than aspirin, are as easy to use and at least as effective as aspirin. Finally, because patients with severer heart failure are likely to be those with very low ejection fractions, these patients are good candidates for oral anticoagulation even though this treatment requires additional monitoring.

Predictive risk factors for pulmonary oxygen transfer in patients undergoing coronary artery bypass grafting

The ratio of arterial oxygen tension to inspired oxygen fraction (PaO2/FiO2) is a useful indicator for weaning patients from mechanical ventilation and a reliable predictor of pulmonary dysfunction after cardiac surgery. The aim of this study was to elucidate the patient characteristics and variables that affect the PaO2/FiO2 ratio. Between 1994-1998, 167 patients who underwent coronary artery bypass grafting (CABG) were examined retrospectively. Spearman's correlation coefficients were calculated between the PaO2/FiO2 ratio and intubation period, and length of ICU stay. Patients were then divided into two groups with a PaO2/FiO2 ratio < 350 and PaO2/FiO2 ratio > or = 350. Univariate analysis of the putative risk factors was performed. A logistic regression model was developed to evaluate factors that would influence the PaO2/FiO2 ratio. A significant correlation was observed between the PaO2/FiO2 ratio and intubation period, and length of ICU stay. Univariate predictors of a PaO2/FiO2 ratio < 350 were low body weight, low preoperative PaO2 long operation time, high FiO2, low postoperative PaO2 history of smoking, hypertension and opening of pleura (p < 0.05). Excellent prediction was found with a model consisting of preoperative PaO2 and hypertension.

CONCLUSION

The results of this study suggest that patients with a low preoperative PaO2 or hypertension may need more careful peri- and postoperative management since these factors are closely associated with the PaO2/FiO2 ratio.

The influence of left ventricular geometry on coronary vasomotion in patients with essential hypertension

The objective of this study was to assess the influence of left ventricular (LV) geometric pattern on coronary vasomotion in patients with essential hypertension. We studied 34 hypertensive patients, who had never been treated, with angiographically normal coronary arteries. Patients were classified into four LV geometric patterns by echocardiography: normal, concentric remodeling, eccentric hypertrophy, and concentric hypertrophy. The responses of coronary vasomotion in left anterior descending artery to vasoactive agents (acetylcholine, isosorbide dinitrate, adenosine triphosphate) were examined using a Doppler guidewire and quantitative coronary angiography. The percent increase in coronary blood flow evoked with acetylcholine (endothelium-dependent vasomotion) showed lowest in concentric hypertrophy, followed by eccentric hypertrophy, concentric remodeling, and normal geometry. The significant linear relationship between acetylcholine-induced coronary blood flow and LV mass was noted. There was no difference in the percent increase in coronary blood flow evoked with isosorbide dinitrate (endothelium-independent vasomotion of conduit vessel) among the four groups. The percent increase in coronary blood flow evoked with adenosine triphosphate (endothelium-independent vasomotion of resistant vessel) was significantly lower in patients with concentric hypertrophy than in the other three groups. The results in this study suggest that coronary vasomotion may be associated with LV geometry in patients with hypertension. The endothelium-dependent vasodilation is impaired progressively as LV hypertrophy advances. The endothelium-independent vasodilation of microvessels is impaired only in concentric hypertrophy. This advanced abnormality of coronary vasomotion may contribute to the high cardiovascular morbidity and mortality in patients with concentric hypertrophy.

Acute hemodynamic interaction of aspirin and ticlopidine with enalapril: results of a double-blind, randomized comparative trial

BACKGROUND

Coprescription of aspirin and ACE inhibitors is frequent in heart failure caused by coronary artery disease. Negative interaction between aspirin and enalapril has been reported, presumably through inhibition by aspirin of ACE inhibitor-induced prostaglandin synthesis. Ticlopidine is a potent antiplatelet agent without interaction with prostaglandin synthesis.

METHODS AND RESULTS

The objective of this study was to compare the influence of a coadministration of ticlopidine or aspirin on the hemodynamic effects of an ACE inhibitor (enalapril) in patients with chronic heart failure. Twenty patients with severe heart failure were enrolled in a double-blind comparative trial and allocated to ticlopidine (500 mg daily, 12 patients) or aspirin (325 mg daily, 8 patients). Hemodynamic evaluation was performed after 7 days of treatment, every hour for 4 hours after an oral administration of 10 mg of enalapril. Significant reductions in systemic vascular resistance were observed in the ticlopidine group, in contrast to no significant decrease in the aspirin group. A significant (P=0.03) time-by-treatment interaction indicated significant aspirin-enalapril drug interaction. Total pulmonary resistance decreased significantly in both groups, with no difference between patients assigned to aspirin or ticlopidine.

CONCLUSIONS

Enalapril reduced systemic vascular resistance more effectively when given in combination with ticlopidine than with aspirin. In contrast, the reduction in total pulmonary resistance is similar when enalapril is administered in combination with aspirin or ticlopidine. Negative aspirin-enalapril interaction on prostaglandin synthesis presumably alters vasodilatation in systemic vessels, whereas prostaglandin-independent actions of ACE inhibition such as pulmonary arterial vasodilatation are maintained.

Angiotensin-converting enzyme inhibitors

ACE inhibitors have achieved widespread usage in the treatment of cardiovascular and renal disease. ACE inhibitors alter the balance between the vasoconstrictive, salt-retentive, and hypertrophic properties of angiotensin II (Ang II) and the vasodilatory and natriuretic properties of bradykinin and alter the metabolism of a number of other vasoactive substances. ACE inhibitors differ in the chemical structure of their active moieties, in potency, in bioavailability, in plasma half-life, in route of elimination, in their distribution and affinity for tissue-bound ACE, and in whether they are administered as prodrugs. Thus, the side effects of ACE inhibitors can be divided into those that are class specific and those that relate to specific agents. ACE inhibitors decrease systemic vascular resistance without increasing heart rate and promote natriuresis. They have proved effective in the treatment of hypertension, they decrease mortality in congestive heart failure and left ventricular dysfunction after myocardial infarction, and they delay the progression of diabetic nephropathy. Ongoing studies will elucidate the effect of ACE inhibitors on cardiovascular mortality in essential hypertension, the role of ACE inhibitors in patients without ventricular dysfunction after myocardial infarction, and the role of ACE inhibitors compared with newly available angiotensin AT1 receptor antagonists.

Platelet eicosanoids and the effect of captopril in blood pressure regulation

We investigated the eicosanoid synthesis of platelets of Wistar and of Okamoto spontaneously hypertensive rats (SHR), and the effect of captopril in vitro, using [14C]arachidonic acid as a tracer substrate and chromatographic determination. Lipoxygenase activity was elevated, while the formation of cyclooxygenase products was reduced in SHR platelets, compared to those of Wistar rats. This difference might play a role in the pathomechanism of hypertension in SHR. In SHR with lower blood pressure, captopril reduced thromboxane synthesis, while in SHR with higher blood pressure thromboxane synthesis was unchanged, but the synthesis of prostaglandin D2, a potent vasodilator, and of 12-L-hydroxy-5,8,10-heptadecatrienoic acid, a stimulator of endothelial prostacyclin formation, was increased. We may conclude that, in spite of the missing angiotensin converting enzyme in platelets, a direct effect on platelet eicosanoid synthesis could contribute to the blood pressure decreasing effect of captopril.

Relative contribution of angiotensin II, bradykinin, and prostaglandins to the renal effects of converting enzyme inhibition in rats after chronic myocardial infarction

We wished to determine whether enhanced bioavailability of bradykinin (BK) and vasodilatory prostaglandins contribute to renovascular and sodium-handling effects of angiotensin-converting enzyme (ACE) inhibition after myocardial infarction (MI). We studied rats after coronary artery ligation treated for 3 weeks with captopril or losartan (2 g/L drinking water for each agent). Hemodynamic and renal function studies were performed in conscious rats before and after sequential infusion BK inhibitor (BKI, 0.02 ng/kg/min) and indomethacin (1 mg/kg). Myocardial infarction increased filtration fraction (FF) 20% (p < .004) but did not change glomerular filtration rate (GFR), urine flow (UF), renal blood flow (RBF), renal vascular resistance (RVR), urine sodium (UNa), or fractional excretion of sodium (FENa). Captopril decreased (p < 0.001) mean arterial pressure (MAP) 25%, UF 61%, RVR 65%, and FENa 75% and increased (p < 0.05) GFR 22%, and RBF 34%. Losartan decreased (p < 0.05) MAP 27%, UF 52%, RVR 21%, and FENa 44%. In captopril-treated MI rats, BKI decreased (p < 0.05) GFR 22% and RBF 25% and increased (p < 0.05) RVR 32%, UNa 43%, and FENa 28%, whereas indomethacin decreased (p < 0.05) GFR 24% and increased (p < 0.05) UNa 86% and FENa 112%. In losartan-treated MI rats, BKI increased (p < 0.05) UNa 42% and FENa 60%, whereas indomethacin increased (p < 0.05) UNa 79% and FENa 85%. Activation of the BK and prostaglandin systems may play an important role in regulating renal function during chronic ACE inhibition, primarily by enhancing the renal vasodilatory effects of angiotensin II (AII) blockade.

Endothelial control of lower limb blood flow in chronic heart failure

BACKGROUND

Limitation of the blood supply to skeletal muscle in chronic heart failure may contribute to the symptoms of fatigue and diminished exercise capacity. The pathophysiology underlying this abnormality is not known. The purpose of this study was to assess the effect of endothelium dependent and independent vasodilator agents on blood flow in the leg of patients with heart failure.

METHODS AND RESULTS

Blood flow in the leg was measured in patients with heart failure (n = 20) and compared with that in patients with ischaemic heart disease and normal left ventricular function (n = 16) and patients with chest pain and normal coronary arteries (n = 8). External iliac artery blood flow was measured using intravascular Doppler ultrasound and quantitative angiography. Flow was recorded at rest and in response to bolus doses of the endothelium independent vasodilator, papaverine. Endothelium dependent responses were measured by infusion of acetylcholine and substance P. Mean (SEM) baseline blood flow was reduced at rest (2.9 (0.4) v 4.5 (0.3) ml/s, P < 0.001) and vascular resistance was raised (37.4 (3.6) v 27.1 (3.0) units, P < 0.05) in patients with heart failure compared with that in controls. The peak blood flow response to papaverine (8 mg), acetylcholine (10(-7)-10(-5) mol/l), and substance P (5 pmol/min) was reduced in heart failure, with greater impairment of the response to acetylcholine than substance P. There was a correlation between baseline blood flow in the heart failure group and diuretic dose (r = -0.62, P = 0.003), New York Heart Association classification (r = -0.65, P = 0.002), and left ventricular ejection fraction (r = 0.80, P = 0.0004).

CONCLUSIONS

There is reduced blood flow and raised vascular resistance at rest in the legs of patients with heart failure. The degree of impaired blood flow in the leg correlates with the severity of heart failure. There is impairment of the response to both endothelium dependent and independent vasodilators. Abnormal function of the vascular myocyte in heart failure may explain these results as would structural abnormalities of the resistance vessels.

Peripheral haemodynamic effects of inhibition of prostaglandin synthesis in congestive heart failure and interactions with captopril

OBJECTIVES

To investigate the role of prostaglandins in maintaining circulatory homoeostasis in chronic heart failure and the hypothesis that an increase in vasodilatory prostaglandin synthesis may contribute to the actions of angiotensin converting enzyme inhibitors in heart failure.

DESIGN

Randomised, double blind, placebo controlled studies. Cardiac output and renal and limb blood flow were measured after oral indomethacin 50 mg or placebo followed by "open" intravenous infusion of prostaglandin E2 (study A). In a second study the same measurements were made after oral indomethacin 50 mg or placebo was given 30 min before "open" captopril (study B).

METHODS

Blood pressure was measured using a mercury sphygmomanometer. Cardiac output was determined by Doppler interrogation of blood flow in the ascending aorta and echocardiographic measurement of aortic root diameter. Renal blood flow was calculated from the effective renal plasma flow measured by p-aminohippurate clearance and the haematocrit, and glomerular filtration rate by endogenous creatinine clearance. Limb blood flow was measured by venous occlusion plethysmography using mercury in silastic strain gauges. The concentration of plasma prostaglandin E2 was measured by radioimmunoassay.

SETTING

University department of cardiovascular medicine.

PATIENTS

12 patients with chronic stable heart failure before starting treatment with angiotensin converting enzyme inhibitors.

RESULTS

Indomethacin resulted in adverse effects on cardiac output, systemic vascular resistance, renal blood flow, glomerular filtration, urinary sodium excretion, and calf vascular resistance. Changes were reversed with infusion of prostaglandin E2. Pretreatment with indomethacin resulted in the attenuation of the acute increase in cardiac output and decrease in systemic vascular resistance that occurred with captopril. Similarly, an increase in renal blood flow with captopril was attenuated by indomethacin.

CONCLUSIONS

The acute adverse effects of indomethacin on central and peripheral haemodynamic and renal function suggest that prostaglandins have a significant role in the regulation of peripheral blood flow and renal function in patients with stable chronic heart failure. The attenuation by indomethacin of captopril induced improvements in haemodynamic function and renal blood flow is consistent with the hypothesis that captopril may act in part via an increase in prostaglandin synthesis.

Renal functional alterations induced by angiotensin-converting enzyme inhibitors in heart failure

OBJECTIVE

To review the effects of angiotensin-converting enzyme (ACE) inhibitors on renal pathophysiology and the compensatory mechanisms involved in heart failure. A clinical application of the use of these agents in the setting of concomitant heart failure and renal insufficiency also is presented.

DATA SOURCES

A MEDLINE search was conducted using the terms heart failure, congestive; renal insufficiency; and angiotensin-converting enzyme inhibitors.

STUDY SELECTION

All applicable animal and human trials were reviewed.

DATA SYNTHESIS

Advances in the management of heart failure have led to new insights into the complex pathophysiology of this condition, particularly the favorable clinical effects noted with the ACE inhibitors. The net effect of ACE inhibitors on the renin-angiotensin system in patients with heart failure is to augment renal blood flow to a greater extent than cardiac output. Glomerular filtration rate is either unchanged or decreased by ACE inhibition. Sodium excretion is augmented primarily by alterations in glomerular hemodynamic parameters. ACE inhibitors may alter renal tubular function, both directly and indirectly, leading to increased diuresis and natriuresis.

CONCLUSIONS

Although ACE inhibitors exert beneficial pharmacodynamic effects on the renal bed in patients with heart failure, clinical consideration of volume and neurohormonal status prior to institution of therapy is prudent.

Studies on the effect of two angiotensin-converting enzyme inhibitors, captopril and cilazapril, on platelet and vascular prostaglandin metabolism in vivo

We have studied in 12 healthy volunteers the effects of two angiotensin-converting enzyme (ACE) inhibitors, captopril and cilazapril, on vascular and platelet prostaglandin metabolism, in a double-blind, placebo-controlled, randomized cross-over study. Formation of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and thromboxane B2 (TxB2) was measured locally at the site of a microvascular injury. Similar amounts of TxB2 and 6-keto-PGF1 alpha were generated following administration of either ACE inhibitor as compared to placebo. It is concluded that neither captopril nor cilazapril significantly influence vascular and platelet prostaglandin metabolism.

Efficacy of low-dose captopril in addition to furosemide and spironolactone in patients with decompensated liver disease during blunted diuresis

The renin-angiotensin-aldosterone system is activated by diuretics and involved in the diuretic resistance of cirrhotic patients with ascites and oedema. In previous studies relatively high doses of captopril (25-400 mg daily) were unsuccessful in promoting diuresis and natriuresis in these patients. We analyzed the efficacy of a low dose of captopril in eight patients with massive ascites resistant to therapy of salt/fluid restriction and increasing doses of spironolactone and furosemide. Mean duration of diuretic use was 73 days (range 7-240 days). After at least 3 days of observation on 80 mg furosemide and 100 mg spironolactone only, captopril was added. Four out of eight patients responded with an increase in natriuresis and diuresis; daily dose of captopril was 20.6 mg in responders and 26.5 mg in non-responders. After the addition of captopril the mean weight change was -7.5 kg in responders and +0.25 kg in non-responders. Mean urinary sodium output in responders increased from 72.8 (S.D. = 35.2) to 128.5 (63.5) mmol within 10 days. Increased diuresis in responders made diuretic reduction necessary: mean furosemide from 80 to 53.3 mg, and mean spironolactone from 100 to 68.1 mg. Creatinine clearances remained stable. High levels of plasma renin activity, plasma aldosterone and angiotensin-II were found in all patients. Non-responders showed more severe hyponatremia and higher vasopressin levels. Natriuretic atrial factor (NAF) was in the upper-normal range or slightly elevated in both groups. In non-responders we noticed low levels of cGMP in 24-h urine, compared with responders.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of delayed captopril therapy on left ventricular mass and myonecrosis during acute coxsackievirus murine myocarditis

The effect of captopril on coxsackievirus B3 murine myocarditis was investigated. Thirty-two, 3-week-old mice were infected with coxsackievirus B3 on day 0 of the study, then randomized into a placebo group or a captopril group starting on day 3 of infection. On day 9 of infection, the mice were put to death. Hearts were weighed and processed for light microscopic examination. Heart weight was 125 +/- 19 mg in the control group versus 102 +/- 14 mg in the captopril group (p less than 0.0003). Amount of necrosis as a percentage of left ventricular section was 3.5% (2.0% to 7.5%) in the placebo group versus 2.0% (0.0% to 5.0%) in the captopril group (p less than 0.01). The amount of dystrophic calcification was 5.0% (0.0% to 27.5%) in the placebo group versus 1.3% (0.0% to 20.0%) in the captopril group (p less than 0.01). The extent of the histopathologic involvement by planimetry was 10.2% in the placebo group versus 5.4% in the captopril group (p = 0.052). We conclude that captopril is beneficial in decreasing left ventricular mass and the amount of myocardial necrosis and calcification in the short term in the murine myocarditis model.

Renal effects of angiotensin-converting enzyme inhibition in congestive heart failure

Some studies report that inhibition of angiotensin-converting enzyme (ACE) improves renal function in patients with congestive heart failure, whereas others report that renal deterioration is a frequent complication of treatment with ACE inhibitors. This article explores the mechanisms by which antagonism of the renin-angiotensin system improves kidney function in some patients while causing harm in others. ACE inhibition may alter renal blood flow, glomerular perfusion pressure, basement membrane activity and renal tubular function both directly and indirectly. In most patients, renal function is maintained as other neurohormonal mechanisms compensate for the negative effects and permit the positive effects (such as improved renal flow) to predominate. However, when physiologic characteristics or iatrogenic interventions (such as volume reduction or prostaglandin inhibition) limit the effectiveness of neurohormonal compensation to maintain renal autoregulation, clinically important deterioration in renal function may occur. An understanding of the renal effects of ACE inhibitors permits their safe and effective use in most patients with congestive heart failure.

Endocrinologic Warfare: The Role of Angiotensin-Converting Enzyme Inhibitors in Congestive Heart Failure

The angiotensin-converting enzyme (ACE) inhibitors represent the gold standard of vasodilator therapy for congestive heart failure through blunting of the endocrinologic manifestations of heart failure. The future role of these agents may be in the asymptomatic and mild stages of heart failure. ACE inhibitors have been shown to decrease morbidity and mortality with the natural history of this disease being altered. The future will bring many new ACE inhibitors to market, with the challenge for physicians and pharmacists to understand the important distinctions of each specific agent. © 1990 by W.B. Saunders Company.

Beneficial effects of captopril in acute coxsackievirus B3 murine myocarditis

To date, there is no universally accepted therapy for viral myocarditis. We investigated the effect of the angiotensin converting enzyme inhibitor captopril on both early and late phases of coxsackievirus murine myocarditis. Mice were infected with coxsackievirus B3 and were divided into two main protocols. Mice in the early treatment protocol (n = 30) were treated on day 1 after infection with either captopril or saline through day 6 of infection and euthanized on day 6 of infection. In the late treatment protocol, mice (n = 60) were treated starting on day 10 of infection through day 30 of infection with either captopril or saline. Mice were killed on days 20 and 30 of infection. In the early treatment protocol, heart weight was 67 +/- 14 mg in the captopril-treated group versus 98 +/- 17 mg in the control group (p less than 0.0001). The degree of inflammation, necrosis, and dystrophic calcification assessed with a semiquantitative histological score was significantly less in the captopril-treated group. The degree of pathological involvement determined by planimetry of histological sections was 8.1 +/- 7.2% for the captopril-treated group versus 22.5 +/- 10.0% for the saline-treated group (p less than 0.0001). In the late treatment protocol, captopril also caused a reduction in heart weight as compared with controls at day 20 (116 +/- 21 mg in captopril-treated group vs. 166 +/- 34 mg in controls, p less than 0.0001) and also at day 30 (136 +/- 23 mg in captopril-treated group vs. 185 +/- 48 mg in controls, p less than 0.004). On days 20 and 30 of infection, the degree of inflammation, necrosis, and dystrophic calcification was similar in both groups. We conclude that captopril is beneficial in acute coxsackievirus B3 murine myocarditis because it reduces heart weight and necrosis when administered early and reduces heart weight when administered in a delayed manner.

Angiotensin-converting enzyme inhibitors: mechanistic controversies

Many studies have investigated the mechanisms responsible for the therapeutic effects of the angiotensin converting enzyme inhibitors. Initially, the hemodynamic changes that occur with these agents were attributed solely to the inhibition of the renin-angiotensin-aldosterone system in plasma. Further research suggested other mechanisms were operable as a relationship was not always evident between hemodynamic changes and inhibition of the plasma renin-angiotensin-aldosterone system. A relationship between the pharmacodynamics of these agents and the inhibition of vascular and tissue renin-angiotensin systems, however, has been observed. Mechanisms less likely to contribute to the actions of the angiotensin converting enzyme inhibitors are increases in bradykinin and prostaglandin concentrations, or inhibition in the renin-angiotensin system within the central nervous system. Ancillary cardiovascular effects of angiotensin converting enzyme inhibitors offer possible new therapeutic gains. An understanding of these mechanistic controversies and newly-defined cardiovascular actions of angiotensin converting enzyme inhibitors are important to clinicians using these agents.

Endothelin binding to cultured calf adrenal zona glomerulosa cells and stimulation of aldosterone secretion

Endothelins are a group of potent vasoconstrictors whose structure was deduced from genomic DNA. ET-1 was first isolated from culture supernatants from porcine endothelial cells and ET-3 was identified from a rat DNA library. We report on the binding of 125I-ET-1 to zona glomerulosa cells in culture and on its ability to stimulate aldosterone secretion. Cultured calf adrenal zona glomerulosa cells have saturable, high affinity [Kd = 1.00 +/- 0.17 X 10(-10) M (SEM)] receptors which bind ET-1 in a temperature and time dependent manner. Binding was specific and angiotensin II, vasopressin, ANP, BNP, apamin, calcium channel agonists or antagonists did not interact with the receptor. ET-3 displaced 125I-ET-1 from the receptor with a relative potency of 0.39 +/- 0.1% (SEM) that of ET-1. ET-1 incubated with cultured glomerulosa cells stimulated aldosterone secretion in a dose dependent manner but it was less potent than angiotensin II. ET-3 had less than 1% the relative potency of ET-1 stimulating aldosterone secretion. This data suggest that ET-1 is an independent stimulator of aldosterone secretion and we are speculating that it might be important in those situations, like in malignant hypertension, where endothelial damage might result in increased ET-1 production.

Contrasting peripheral short-term and long-term effects of converting enzyme inhibition in patients with congestive heart failure. A double-blind, placebo-controlled trial

To discover the underlying mechanisms involved in the beneficial long-term effects of angiotensin converting enzyme (ACE) inhibitors, we investigated the systemic and peripheral effects of short- and long-term ACE inhibition in patients with chronic heart failure. After assessing the short-term effects and dose titration with cilazapril, a new long-acting ACE inhibitor, 21 patients were randomized to receive either placebo or the ACE inhibitor. Seventeen patients completed the 3-month treatment. Central hemodynamic output, femoral blood flow (measured by thermodilution), oxygen saturation, and lactate and norepinephrine levels were determined simultaneously in the femoral vein and radial artery during treatment and after a 3-month rest and during symptom-limited bicycle exercise. Short-term ACE inhibition improved rest and exercise hemodynamic output, but it did not alter peak femoral blood flow, calculated leg oxygen consumption, or systemic oxygen uptake during exercise, despite significant reduction in femoral norepinephrine extraction and arterial angiotensin levels during exercise. In contrast, long-term ACE inhibition further improved exercise cardiac output and increased leg blood flow (from 2.3 to 2.9 l/min, p less than 0.05), leg oxygen consumption (from 277 to 403 ml/min, p less than 0.05), and systemic oxygen uptake (from 1,133 to 1,453 ml/min, p less than 0.05), whereas these variables remained unchanged with placebo treatment (p less than 0.02 between groups). Moreover, a moderate but significant increase in femoral oxygen extraction occurred after long-term therapy (ACE inhibitor: from 76% to 83%, p less than 0.05; placebo: from 75% to 74%, NS; p less than 0.01 between groups). We conclude that long-term ACE inhibition is clinically beneficial in that it improves blood flow to skeletal muscle during exercise over time. The long-term effects of ACE inhibition are, in part, probably related to peripheral (vascular) mechanisms, for example, by reversing the inability of peripheral vessels to dilate and by improving oxygen utilization.

Angiotensin converting enzyme inhibitors. II. Clinical use

Since their introduction in clinical practice in 1980, ACE inhibitors have been found useful in the treatment of hypertension and CHF. In hypertension, they are effective as monotherapy in 40% to 50% of the patients, and in combination with diuretics or calcium antagonists, they are effective in up to 85% of the patients. They are well tolerated, are not associated with depression, impotence, bronchospasm or metabolic derangements such as hypokalemia, hyperuricemia or hyperglycemia, and do not have adverse effects on the quality of life. As a result, they are preferred in hypertensive patients with CHF, left ventricular dysfunction, mental depression, older age, coronary artery disease, metabolic disorders, chronic destructive pulmonary disease, and peripheral vascular disease. In CHF they cause long-lasting hemodynamic and symptomatic improvement, improve exercise tolerance, and may lower mortality in certain patient subsets. Evolving new indications for ACE inhibitors include the diagnosis of renovascular hypertension, the prediction of surgical success, the treatment of scleroderma renal crisis, the reduction of proteinuria, renal protection, cardioprotection, the improvement of arterial compliance, in Bartter's syndrome and idiopathic edema, etc. ACE inhibitors are usually well tolerated but in some instances they may cause class-specific side effects such as hypotension; usually reversible azotemia or renal failure, especially in patients with renal artery stenosis or with CHF with low blood pressure; cough; angioedema; and hyperkalemia. Differences among ACE inhibitors are emerging and include chemical class (e.g., zinc ligand), biotransformation, potency, pharmacokinetics, prodrugs, tissue effects, additional pharmacologic properties, and drug interactions.

Skeletal muscle blood flow, metabolism and morphology in chronic congestive heart failure and effects of short- and long-term angiotensin-converting enzyme inhibition

Blood flow to skeletal muscle during exercise is limited in patients with chronic congestive heart failure compared with normal persons. This may, in part, be attributed to the inability of the vessels to dilate adequately. In addition, an abnormal skeletal muscle metabolism with oxidative capacity can be demonstrated in patients with chronic congestive heart failure. The latter may partially explain why vasodilators and inotropes that improve central hemodynamics, global leg perfusion or skeletal muscle blood flow during exercise do not increase oxygen uptake by working muscle after acute drug administration. Furthermore, increases in blood flow to skeletal muscle may be redistributed to inactive or less oxygen-dependent muscle fibers. Although acute angiotensin-converting enzyme inhibition usually neither exerts substantial improvement in exercise hemodynamics nor interferes with leg perfusion during exercise, skeletal muscle blood flow and oxygen uptake gradually increases with long-term angiotensin-converting enzyme therapy, leading to improved systemic oxygen consumption and exercise tolerance. Several factors, such as reduction in plasma and vascular angiotensin II and sympathetic nervous activity, increased prostaglandin levels and renal function may contribute to this beneficial long-term effect.