Renin- and non-renin-mediated antihypertensive actions of converting enzyme inhibitors

Factors Influencing Arteriovenous Fistula Dysfunction in Japanese Patients on Chronic Hemodialysis

Arteriovenous fistula dysfunction is a constant problem in chronic hemodialysis patients. We investigated the factors influencing fistula dysfunction in 184 patients on chronic hemodialysis. Stepwise regression analysis and Cox proportional hazards model were used to assess the relationship between fistula dysfunction and age, sex, duration of hemodialysis, diabetes mellitus, hematocrit, serum creatinine, blood urea nitrogen, KW, prothrombin time, blood pressure, anticoagulant therapy, dose of erythropoietin, calcium channel blocker therapy, and angiotensin-converting enzyme inhibitor therapy. Fistula dysfunction showed a significant relationship with a low systolic blood pressure, a low hematocrit, the presence of diabetes mellitus, and angiotensin-converting enzyme inhibitor therapy. These results suggested that treatment with angiotensin-converting enzyme inhibitors may help to prevent fistula dysfunction.

Effect of Ketoprofen on Blood Pressure, Endocrine and Renal Responses to Chronic Dosing with Captopril in Patients with Essential Hypertension

The effects of non-steroidal anti-inflammatory drugs (NSAIDs) on the blood pressure and renal function of essential hypertensive patients depend on the specific type of NSAID and antihypertensive drug administered. Twelve patients with essential hypertension, aged 35 to 59 years, stabilized (blood pressure less than 140/90 mmHg) with captopril, received ketoprofen (100 mg bid for 7 days) or matching placebo in a randomized double-blind cross-over fashion. A 3-week wash-out period was included between treatment periods. Blood pressure on the first and last days of the placebo treatment period (137 +/- 7 (SD)/80 +/- 8 and 139 +/- 11/81 +/- 9 mmHg) was similar to respective values during ketoprofen therapy (136 +/- 10/79 +/- 7 and 143 +/- 10/81 +/- 9 mmHg). The mean differences in systolic and diastolic blood pressures, at the end of the treatment periods, between ketoprofen and placebo were 4 (95% confidence intervals -5, +13) and 0 (-8, +8) mmHg, respectively. Ketoprofen had no effect on 24-h urinary sodium excretion (160 +/- 33 and 147 +/- 39 mmol/24 h for ketoprofen and placebo, respectively). Ketoprofen was without effect on glomerular filtration rate, renal plasma flow and filtration fraction. In conclusion, our data suggest that ketoprofen is a safe choice when short-term treatment with a NSAID is indicated in an essential hypertensive patient treated with a converting enzyme inhibitor such as captopril.

Hypotension Due to Interaction Between Lisinopril and Tizanidine

OBJECTIVE

To report a case in which significant hypotension occurred after initiation of tizanidine in a patient using the antihypertensive agent lisinopril.

CASE SUMMARY

A 48-year-old woman was admitted due to cerebral hemorrhage at the midbrain and pons, with extension to the fourth ventricle. Consciousness disturbance (Glasgow coma scale 4) with a decerebrate posture improved 5 days after stroke onset. As the BP was fairly high, antihypertensive agents, including lisinopril, were initiated. Three weeks later, the decerebrate rigidity and high BP remained, and tizanidine was initiated to see whether the decrease in muscle tone could facilitate hypertension control and motor recovery. However, the BP dropped dramatically within 2 hours after the first dose of tizanidine. The tizanidine and all of the antihypertensive medications were withdrawn. Tizanidine was used again after her BP had stabilized, but did not produce similar problems.

DISCUSSION

A similar event was reported in 2000. The reaction in our patient appeared after tizanidine initiation and improved after both lisinopril and tizanidine were discontinued. According to the Naranjo probability scale, this was classified as a possible drug interaction. This kind of reaction is seldom mentioned as occurring during co-administration with tizanidine. With its characteristics, tizanidine has the potential to compromise hemodynamic stability during concomitant angiotensin-converting enzyme inhibitor use.

CONCLUSIONS

Based upon the literature review, the hypotension in this patient was possibly due to the interaction between tizanidine and lisinopril.

Elevated dietary salt suppresses renin secretion but not thirst evoked by arterial hypotension in rats

Increased dietary salt intake was used as a nonpharmacological tool to blunt hypotension-induced increases in plasma renin activity (PRA) in order to evaluate the contribution of the renin-angiotensin system (RAS) to hypotension-induced thirst. Rats were maintained on 8% NaCl (high) or 1% NaCl (standard) diet for at least 2 wk, and then arterial hypotension was produced by administration of the arteriolar vasodilator diazoxide. Despite marked reductions in PRA, rats maintained on the high-salt diet drank similar amounts of water, displayed similar latencies to drink, and had similar degrees of hypotension compared with rats maintained on the standard diet. Furthermore, blockade of ANG II production by an intravenous infusion of the angiotensin-converting enzyme inhibitor captopril attenuated the hypotension-induced water intake similarly in rats fed standard and high-salt diet. Additional experiments showed that increases in dietary salt did not alter thirst stimulated by the acetylcholine agonist carbachol administered into the lateral ventricle; however, increases in dietary salt did enhance thirst evoked by central ANG II. Collectively, the present findings suggest that hypotension-evoked thirst in rats fed a high-salt diet is dependent on the peripheral RAS despite marked reductions in PRA.

Effects of aspirin on N-alpha-tosyl L-arginine methyl ester [TAME]-esterase induced contractions on rat aorta in vitro

The present study was designed to investigate whether N-alpha-tosyl L-arginine methyl ester [TAME]-esterase activation could be the result of endothelial dysfunction. Thoracic aorta from rats was mounted in an organ bath containing Krebs solution. Intact and endothelium denuded aortic strips were challenged with different concentrations of TAME (10(-15)-10(-1) m). The effects of aspirin, a cyclo-oxygenase pathway inhibitor, were also studied on [TAME]-esterase induced contraction on rat aorta strips. Our results showed that aspirin definitely blocked TAME-esterase induced contractions on rat aortic strips. In conclusion, the present work supported the hypothesis that [TAME]-esterase induced contraction in rat aorta in vitro was mediated through release of prostaglandin(s) as a result of endothelial dysfunction.

[Effect of angiotensin blockade on the orthostatic response in patients with systemic arterial hypertension]

INTRODUCTION AND OBJECTIVES

The effect of the treatment of arterial hypertension with angiotensin inhibitors on the autonomic response to orthostatism was studied.

PATIENTS AND METHOD

In 20 hypertensive patients, enalapril (10 to 20 mg) was administered daily for four weeks. Then, irbesartan (150 to 300 mg) was given for four weeks. Finally, 10 mg of enalapril combined with 150 mg of irbesartan was prescribed for another four weeks. Heart rate variability at rest and during the head-up tilt test with controlled respiration was assessed at the beginning and end of each period.

RESULTS

Mean arterial pressure showed a similar reduction in the three treatment periods. There were no changes in heart rate. Heart rate variability at rest showed differences in the spectral high-frequency component between the control and the treatment periods (p = 0.10). There was an increase in the high-frequency component between the control and the third (p = 0.047) and the fourth periods (p = 0.03). In the head-up tilt test there was a decrease in total spectral high-frequency power.

CONCLUSIONS

There was no increase in orthostatic intolerance with these drugs in hypertensive patients. The absence of changes in heart rate in spite of a decrease in blood pressure suggests resetting of the baroreflex function. The long-term control of hypertension with these drugs may have a favorable effect on heart rate variability, with an increase in parasympathetic activity.

Does aspirin attenuate the effect of angiotensin-converting enzyme inhibitors on health outcomes of very old patients with heart failure?

OBJECTIVES

Concomitant ischemic heart disease (IHD) is common in older individuals with heart failure (HF). We estimated the effect of aspirin use on the rate of mortality, morbidity, and decline in physical functioning in nursing home residents with HF taking angiotensin-converting enzyme (ACE) inhibitors.

DESIGN

We conducted a retrospective cohort study using a nursing home database linking resident information collected via the Minimum Data Set (MDS) with drug utilization data.

SETTING

Nursing homes in four states (1992-1995).

PARTICIPANTS

Of 49,779 residents with HF admitted to these homes, 12,703 residents were taking an ACE inhibitor; 2,046 of these took aspirin.

MEASUREMENTS

Medicare enrollment files provided the date of death, and we used the Part A Medicare files to identify hospital admissions. The activity of daily living scale from repeat MDS assessments allowed us to evaluate decline in physical function. Cox proportional hazards models provided adjusted estimates of the aspirin effect, with nonusers as the reference group.

RESULTS

The overall mortality rate, hospitalization rate,and rate of decline in physical function of aspirin users were not different from those of nonusers (e.g., hospitalization rate ratio = 0.99, 95% confidence interval = 0.92-1.07). This effect did not vary by presence of concomitant IHD or by dose or type of ACE inhibitor.

CONCLUSION

In a cohort of older HF residents receiving ACE inhibitors in nursing homes, we found that treatment with aspirin did not appear to affect outcomes negatively.

Effect of angiotensin-converting enzyme inhibitor on renal function in ovarian hyperstimulation syndrome in the rabbit

OBJECTIVE

To investigate renal function and whether captopril prevents alterations in the handling of sodium and water in the ovarian hyperstimulation syndrome (OHSS) in the rabbit.

DESIGN

Experimental study

SETTING

Physiology laboratory.

ANIMAL(S)

Six female New Zealand white rabbits were used as controls, and 13 were hyperstimulated with gonadotropins.

INTERVENTION(S)

Saline or captopril.

MAIN OUTCOME MEASURE(S)

Renal excretory and hemodynamic variables.

RESULT(S)

The 3% extracellular volume expansion in OHSS animals induced a significant elevation in mean arterial pressure by 27%, although increments in natriuresis and diuresis were similar to those observed in controls. The OHSS group had impaired pressure-natriuresis sensitivity compared with controls (0.36 +/- 0.07 microEq/min/g of Na excreted per mm Hg vs. 1.74 +/- 0.45 microEq/min/g of Na excreted per mm Hg; P<.05. Captopril significantly reduced mean arterial pressure (P<.05) and shifted the pressure-natriuresis response to the left by 0.85 +/- 0.17 microEq/min/g of Na excreted per mm Hg (P<.05).

CONCLUSION(S)

In OHSS in the rabbit model, pressure-natriuresis sensitivity is impaired. Angiotensin II may play a significant role in this phenomenon, since angiotensin-converting enzyme inhibition normalized the pressure-natriuresis relationship.

Plasma levels of nitric oxide and related vasoactive factors following long-term treatment with angiotensin-converting enzyme inhibitor in patients with essential hypertension

Several mechanisms other than the inhibition of systemic and local formation of angiotensin II (Ang II) have been proposed to play a role in mediating the hypotensive effects of angiotensin-converting enzyme (ACE) inhibitors. In the present study, we measured plasma levels of nitric oxide (NO) and the related vasoactive factors bradykinin, 6-keto prostaglandin F1alpha (6-keto PGF1alpha) a stable metabolite of prostacyclin, and cyclic guanosine-3',5'-monophosphate (cGMP) before and after a 4-week treatment with the ACE inhibitor lisinopril in 17 patients with essential hypertension. Plasma NO levels were measured by the Griess method after conversion of nitrate to nitrite. Long-term lisinopril treatment significantly reduced blood pressure and increased plasma NO and 6-keto PGF1alpha. The treatment also tended to increase plasma levels of bradykinin and cGMP, but not to a significant extent. The posttreatment NO level was inversely correlated with posttreatment systolic, diastolic, and mean blood pressure (n = 17, r= -.68, P< .01, n = 17, r= -.54, P < .05, and n = 17, r= -.66, P< .01, respectively). The posttreatment bradykinin level was also modestly correlated with posttreatment systolic and mean blood pressure (n = 17, r = -.51, P < .05 and n = 17, r = -.55, P < .05, respectively). In contrast, posttreatment 6-keto PGF1alpha and cGMP levels were not correlated with posttreatment systolic, diastolic, or mean blood pressure. These findings raise the possibility that increased formation of NO and bradykinin, as well as inhibition of the renin-angiotensin system, contribute to the hypotensive effect of the ACE inhibitor observed in our hypertensive patients.

Angiotensin-converting enzyme inhibition and AT1 receptor blockade modify the pressure-natriuresis relationship by additive mechanisms in rats with human renin and angiotensinogen genes

The intrarenal factors responsible for hypertension in double-transgenic rats (dTGR) harboring human renin and human angiotensinogen genes are unclear. The pressure-natriuresis and -diuresis relationships in response to chronic angiotensin-converting enzyme (ACE) inhibition and AT1 receptor blockade were evaluated. Renal renin-angiotensin and nitric oxide (NO) system gene expression was also investigated. Six-week-old dTGR were treated for 3 wk with submaximal doses of cilazapril (10 mg/kg, orally) or losartan (10 mg/kg, orally) or with the drug combination. In untreated dTGR, pressure-natriuresis relationships were maximally shifted rightward by approximately 70 to 80 mmHg, and both renal blood flow (RBF) and GFR were markedly decreased. Submaximal cilazapril and losartan dosages both decreased systolic BP by 30 mmHg and shifted the pressure-natriuresis curves leftward by 25 to 30 mmHg. Cilazapril increased RBF and GFR to values observed in normotensive control animals but did not significantly affect fractional sodium excretion (FENa) or fractional water excretion (FEH2O) curves. In contrast, losartan had no significant effect on RBF or GFR but shifted the FENa and FEH2O curves leftward. The cilazapril and losartan combination completely normalized BP and shifted the pressure-natriuresis curves leftward more than did either drug alone. When cilazapril and losartan were administered at higher doses (30 mg/kg, orally), the two drugs equally shifted the pressure-natriuresis curves leftward, by 50 mmHg. Both drugs increased RBF and GFR; however, only losartan shifted FENa and FEH2O curves leftward. Human and rat renin and angiotensinogen genes were downregulated in dTGR and were increased by losartan and cilazapril treatments, whereas no changes in the expression of rat ACE and AT1A receptor genes were observed. Endothelial NO synthase expression was increased by cilazapril but not by losartan. Neither inducible NO synthase nor neural NO synthase gene expression was affected by drug treatments. Therefore, submaximal ACE inhibition enhanced sodium excretion mainly by increasing RBF and GFR, whereas submaximal AT1 receptor blockade decreased tubular sodium and water reabsorption. The combination of the two drugs produced an additive effect. The ACE inhibitor effects may involve increased endothelial NO synthase expression, perhaps related to the inhibition of bradykinin degradation.

Evidence-based medicine and ACE inhibition

The use of angiotensin-converting enzyme (ACE) inhibitors has been generally beneficial in the treatment of many clinical conditions characterized by a significant degree of cardiovascular and renal involvement. Most of the available data on the benefits of ACE inhibitors have come from well-conducted large clinical trials that have provided much information supporting the use of ACE inhibitors, in agreement with the basic principles of evidence-based medicine. In particular, ACE inhibitors improve blood pressure control in patients with hypertension and have proved to be beneficial in patients with left ventricular (LV) systolic dysfunction and chronic congestive heart failure (CHF). Improved survival rates after the use of ACE inhibitors have been also demonstrated in patients with acute myocardial infarction (MI), whether or not the condition is complicated by acute CHF. More recently, some studies have demonstrated the ability of ACE inhibitors (particularly fosinopril) to prevent the long-term development of CHF in patients treated acutely during MI and without baseline LV dysfunction. ACE inhibitors appear to improve the long-term prognosis of patients with coronary artery disease (CAD) and to reduce the occurrence of re-infarction, as demonstrated in the Studies of Left Ventricular Dysfunction (SOLVD) trial and the Survival and Ventricular Enlargement study (SAVE). Finally, a protective role for ACE inhibitors has been reported even in diabetic hypertensive patients, in whom such agents can significantly reduce the occurrence of major cardiovascular events (CAD and stroke) with a pattern that is largely independent of blood pressure control and is not observed with the use of calcium antagonists. These data confirm the strong involvement of the renin-angiotensin system in the pathophysiology of vascular diseases and strongly support the role of ACE inhibitors as drugs for present and future therapy.

Comparison of effects of enalapril and nitrendipine on cardiac sympathetic nervous system in essential hypertension

OBJECTIVES

The purpose of this study was to assess the effects of enalapril and nitrendipine on the cardiac sympathetic nervous system.

BACKGROUND

Angiotensin-converting enzyme inhibitors and long-acting calcium channel blockers have been widely used in the treatment of cardiovascular diseases, in some of which sympathetic overactivity plays a major role in the pathophysiology and prognosis. However, little information is available on the effects of these drugs on the cardiac sympathetic nervous system.

METHODS

123I-metaiodobenzylguanidine (MIBG) cardiac imaging was performed before and 3 months after drug administration in 46 patients with mild essential hypertension. Twenty-two patients were treated with 5 to 10 mg of enalapril once a day, and the other 24 with 5 to 10 mg of nitrendipine once a day. For comparison, 20 normotensive subjects were also studied.

RESULTS

There were no significant differences between the basal characteristics in the 2 hypertensive groups. In both hypertensive groups, both systolic and diastolic blood pressures were significantly reduced to similar levels after the 3-month drug treatment. Before the drug treatment, the 2 hypertensive groups had a significantly higher washout rate and lower MIBG uptake than the normotensive subjects. The heart-to-mediastinum ratio significantly increased (p < 0.0001), with decreased (p < 0.002) washout rate after drug treatment in the enalapril group, but with no significant changes in the nitrendipine group.

CONCLUSION

Enalapril could suppress cardiac sympathetic activity and nitrendipine had no effect on it. The knowledge of antihypertensive drugs on the cardiac sympathetic nervous system appears to be helpful in selecting appropriate treatment in cardiovascular diseases.

ACE Inhibitors and Renal Vascular Responses in the Spontaneously Hypertensive Rat

BACKGROUND: Substantial evidence has accumulated for the intrarenal generation of functionally important quantities of angiotensin II (Ang II). To assess the possibility that Ang II generation occurs beyond a barrier to diffusion from the vascular compartment, six angiotensin-converting enzyme (ACE) inhibitors varying widely in their lipid solubility were employed in the spontaneously hypertensive rat (SHR) and their normotensive controls (WKY). The biological end points were renal blood flow and its response to Ang II. RESULTS: Two ACE inhibitors, ramipril and captopril, induced a larger increase in renal blood flow and enhanced the renal vascular response to Ang II substantially more than did enalapril and lisinopril. The two prodrugs, enalapril and ramipril, which are substantially more lipophilic than the respective active drugs, enalaprilat and ramiprilat, showed equivalent responses. The partial agonist saralasin virtually abolished the renal vasodilator response to ramipril. The pattern of response was similar in WKY, but the responses were substantially smaller. CONCLUSIONS: The results support the concept that a functionally important compartment for intrarenal Ang II formation exists in the healthy rat and that this process is amplified in the SHR.

Changes in glomerular filtration rate and renal plasma flow in cirrhotic rats during converting enzyme inhibition

During the development of cirrhosis ascites-edema, peripheral vasodilatation, hypotension and an increase of the plasma concentration of several neurohormones are frequently observed. Such complex changes in the hormonal profile hinders the assessment of the relative role of each in the pathophysiology of this disease. The purpose of this work was to evaluate in a rat model of experimental cirrhosis (phenobarbital/CCl4) the role of the renin-angiotensin system in the pre-ascitic stage of the disease using the converting enzyme inhibitor captopril. Cirrhotic rats showed diminished renal and hepatic perfusion. Compared to normal rats, glomerular filtration rate in cirrhotic rats was reduced from 0.75 +/- 0.11 to 0.42 +/- 0.06 mL/min/100 g BW, and renal plasma flow was reduced from 2.37 +/- 0.28 to 1.58 +/- 0.16 mL/min/100 g BW; the indocyanine green slope changed from -0.095 +/- 0.028 to -0.057 +/- 0.01; the plasma sodium concentration fell from 144 +/- 1.5 to 131 +/- 5.40 mEq/L (all < .05). The mean arterial pressure was not reduced in the cirrhotic rats. There was no ascites. Both the acute (25 mg i.v.) and chronic (25 mg i.p. daily plus 25 mg/L in drinking water) administration of captopril to cirrhotic rats induced an increase in glomerular filtration rate and renal plasma flow along with a steeper slope in indocyanine green decay (p < .05 for all three parameters) when compared to non-treated cirrhotic animals. No changes were observed in controls. In the balance studies, an increase in urinary volume along with a decrease in urinary osmolality was recorded in cirrhotic rats on chronic captopril treatment. In conclusion, our results show an activation of the renin-angiotensin system in these rats, as disclosed by the inhibition of the converting enzyme, as well as a possible interaction with ADH.

Factors Influencing Arteriovenous Fistula Dysfunction in Japanese Patients on Chronic Hemodialysis

Arteriovenous fistula dysfunction is a constant problem in chronic hemodialysis patients. We investigated the factors influencing fistula dysfunction in 184 patients on chronic hemodialysis. Stepwise regression analysis and Cox proportional hazards model were used to assess the relationship between fistula dysfunction and age, sex, duration of hemodialysis, diabetes mellitus, hematocrit, serum creatinine, blood urea nitrogen, Kt/V, prothrombin time, blood pressure, anticoagulant therapy, dose of erythropoietin, calcium channel blocker therapy, and angiotensin-converting enzyme inhibitor therapy. Fistula dysfunction showed a significant relationship with a low systolic blood pressure, a low hematocrit, the presence of diabetes mellitus, and angiotensin-converting enzyme inhibitor therapy. These results suggested that treatment with angiotensin-converting enzyme inhibitors may help to prevent fistula dysfunction.

Preventative and therapeutic effects of AE0047 on renal injury in stroke-prone spontaneously hypertensive rats

1. The present study was designed to investigate the preventative and therapeutic effects of AE0047 on renal injury compared with those of nitrendipine in stroke-prone spontaneously hypertensive rats (SHRSP). 2. In the preventative study, drug administration was started before the appearance of renal injury, such as proteinuria. Treatment for 6 weeks with AE0047 (1 and 3 mg/kg, p.o.) led to a dose-related reduction in systolic blood pressure (SBP). Nitrendipine, at doses of 10 and 30 mg/kg, also lowered SBP to a similar degree to that seen with AE0047 at 1 and 3 mg/kg, respectively. 3. In the vehicle-administered SHRSP group, urinary excretion of protein (Uprotein V) increased progressively from 14 weeks of age for another 6 weeks. AE0047 at both doses maintained Uprotein V within normal levels throughout the experimental period. However, the elevation of Uprotein V was only inhibited in the 30 mg/kg nitrendipine-treated group. Urinary N-acetyl-beta-D-glucosaminide (NAG) activity in the vehicle-treated SHRSP group was elevated. Urinary NAG activity remained at a low level only in AE0047-treated groups. 4. Histopathological examination revealed severe lesions (i.e. fibrinoid necrosis, proliferative vasculitis and glomerular lesions) of the kidney in SHRSP. AE0047 treatment at each dose attenuated the development of renal lesions in SHRSP. In contrast, nitrendipine, at 10 mg/kg, was ineffective against the development of renal lesions. Although nitrendipine at 30 mg/kg suppressed the development of renal lesions, this effect was still weaker than that seen with AE0047 at 1 mg/kg. 5. In the therapeutic study, drugs were administered to 17-week-old SHRSP with moderate renal damage for 10 days. Treatment with AE0047 (1 and 3 mg/kg) produced dose-dependent decreases in Uprotein V. In the nitrendipine-treated group, Uprotein V tended to decrease but the changes were not significant. 6. Histopathological studies revealed that 3 mg/kg AE0047 improved renal lesions, such as fibrinoid necrosis, proliferative vasculitis and glomerular lesions, whereas 30 mg/kg nitrendipine did not. 7. Taken together, the results indicate that AE0047 is capable of preventing proteinuria as well as renal lesions, in part via a mechanism independent of its depressor action on SBP. Furthermore, AE0047 improves proteinuria and renal lesions in proteinuria-established SHRSP. Thus, AE0047 may have therapeutic potential in suppressing either the development or the progression of renal disease in hypertensive patients.

Beneficial action of beraprost sodium, a prostacyclin analog, in stroke-prone rats

Beraprost sodium is a stable analog of the vasodilator, platelet antiaggregatory eicosanoid, prostacyclin. Experiments were performed to determine whether long-term therapy with beraprost produces vascular protective effects in saline-drinking stroke-prone spontaneously hypertensive rats (SHRSPs). Oral beraprost at 30, 100, or 300 micrograms/kg/day starting at 8.4 weeks of age did not affect the progressive increase of systolic blood pressure (measured by tail-cuff plethysmography) in these rats. Additional experiments in SHRSPs, prepared for continuous monitoring of blood pressure by radiotelemetry, revealed that oral beraprost administration reduced mean arterial pressure but that these hypotensive responses were not sustained (< 4 h). In all SHRSPs receiving oral beraprost, proteinuria and cerebrovascular lesions developed. In contrast, continuous subcutaneous infusion of beraprost at 2.8 mg/kg/day from age 8.3-12.3 weeks reduced systolic blood pressure and markedly diminished the development of renal lesions and the occurrence of stroke in saline-drinking SHRSPs. Beraprost at 0.9 mg/kg/day reduced blood pressure less than did 2.8 mg/kg/day and provided partial protection against cerebral and renal lesions after a 4-week infusion period. These results indicate that long-term subcutaneous infusion of beraprost can protect saline-drinking SHRSPs against stroke and renal damage. This effect is not readily dissociated from the ability of beraprost to reduce blood pressure in SHRSPs.

Effects of the AT1-selective angiotensin II antagonist, telmisartan, on hemodynamics and ventricular function after cardiopulmonary resuscitation in pigs

The purpose of this study was to investigate the effects of the angiotensin II (ANG II) antagonist, telmisartan, on hemodynamics, myocardial function and myocardial blood flow during the postresuscitation phase in a porcine model of CPR and to compare these to saline. After 4 min of ventricular fibrillation and 5 min of closed-chest CPR, defibrillation was performed in 16 domestic pigs to restore spontaneous circulation (ROSC). Ten minutes after ROSC, animals were allocated to receive either the ANG II antagonist, telmisartan, at a dose of 1 mg/kg (n = 8) or saline (n = 8). Hemodynamics, myocardial function and myocardial blood flow were measured prearrest and at 5, 30, 90 and 240 min after ROSC. Using a Swan-Ganz catheter with a fast responding-thermistor and a micromanometer tipped catheter, right ventricular end-diastolic and end-systolic volume, right ventricular ejection fraction, left ventricular contractility were 67 +/- 6 ml (mean +/- S.E.M.), 42 +/- 4 ml, 38 +/- 2%, 2036 +/- 77 mmHg/s in the telmisartan group and 82 +/- 2 ml (P < 0.05), 59 +/- 3 ml (P < 0.01), 28 +/- 2% (P < 0.01), 1596 +/- 82 mmHg/s (P < 0.01) in the control group, at 240 min after ROSC. No significant differences in mean aortic and pulmonary artery pressure, cardiac index or myocardial blood flow between the two groups were found. We conclude that the ANG II antagonist telmisartan administered during the postresuscitation phase in pigs increases myocardial contractility without changing cardiac index, systemic vascular resistance, pulmonary vascular resistance, or myocardial perfusion.

Cardioprotective effect of angiotensin-converting enzyme inhibitors in patients with coronary artery disease

Clinical and experiments study with angiotensin-converting enzyme (ACE) inhibitors suggest that these agents may improve coronary artery disease by acting at multiple sites in the series of events leading to end-stage heart disease. These agents reduce blood pressure, improve prognosis and symptoms in patients with severe heart failure and in patients after acute myocardial infarction with left ventricular dysfunction. They are useful in the early, acute phase of myocardial infarction. More recently, ACE inhibitors have been shown to reduce in vitro vascular hypertrophy, to attenuate arteriosclerosis, and to maintain endothelium function. Whether these effects occur at clinical levels is still uncertain. The exciting clinical data have led to the proposal that alteration of ACE activity, particularly in tissue, is an important factor in development and progression of CAD. The ACE system is complex, with endocrine, paracrine, and autocrine effects. ACE is present in cardiac and vascular tissue. Therefore, the beneficial effects of ACE inhibitors can be classified as "cardio" and "vasculo" protective. This article summarizes a number of independent and complementary mechanisms pointing to a role of ACE and ACE inhibition in coronary artery disease.

Effects of SC-52458, a new nonpeptide angiotensin II receptor antagonist, on increase in cytoplasmic Ca2+ concentrations and contraction induced by angiotensin II and K(+)-depolarization in guinea-pig taenia coli

1. The effects of angiotensin (Ang) II receptor antagonist, SC-52458, on peak and plateau components of Ang II-induced contraction were evaluated in the guinea-pig taenia coli. 2. SC-52458 suppressed both the components of and increases in cytoplasmic Ca2+ concentrations, [Ca2+]i, coupled with the contraction by Ang II; tetrodotoxin and atropine did not affect the contractions. 3. SC-52458 inhibited a plateau component of the contraction induced by K(+)-depolarization to some extent, without affecting a peak component. 4. SC-52458 suppressed both the contraction and increase of [Ca2+]i by antagonizing AT1 receptors in the smooth muscle.

Effects of a single dose and short-term captopril treatment on some pressor and depressor humoral factors in healthy subjects

14 healthy subjects (8 males and 6 females), aged 25-40 years, were studied before and after oral administration of a single dose of 50 mg captopril as well as after 3 d treatment with 100 mg captopril daily per os. We found that in addition to the well-known effects on the renin-angiotensin-aldosterone system, captopril, after 3 d treatment, significantly increases plasma and urinary kallikrein activity, plasma vasopressin and urinary prostaglandin (PG) E2. Atrial natriuretic peptide did not change significantly after either the single dose or the short-term treatment. We conclude that the blood pressure lowering effect of captopril could be mediated by increasing activity of the kallikrein-kinin system and of PGE2 without any participation of atrial natriuretic peptide.

Hemodialyzer performance: biological indices

In the last decade there has been a rapid increase in the number of biological indices that could potentially be used as measures of hemodialyzer or membrane biocompatibility. Consequently, it has become more challenging for all of those involved in renal replacement therapy to evaluate the relative merits of one membrane versus another when faced with their ever increasing variety of parameters. This review attempts to summarize the current array of biological parameters described in the literature as indices of biocompatibility and provide a critique of their utility. Emphasis is placed on measures of activation of the plasma cascade systems, complement, coagulation, and kinin as primary indices of biocompatibility. Additional information on neutrophil, monocyte, platelet, lymphocyte and natural killer (NK) cell effects may provide further insight into blood-membrane mediated interactions although many of these may parallel plasma cascade systems activation. The importance of good statistical design and analysis is emphasized to ensure meaningful interpretation of any study.

Efficacy and tolerability of losartan versus enalapril alone or in combination with hydrochlorothiazide in patients with essential hypertension

The antihypertensive effects and the tolerability of losartan and enalapril given alone or in combination with hydrochlorothiazide (HCTZ) were compared in a multicenter, double-blind, randomized, parallel-group, 16-week clinical trial. The study consisted of a 4-week placebo washout phase and a 12-week active treatment phase. Patients with mild-to-moderate, uncomplicated essential hypertension were considered for participation in the study. To enter the treatment phase of the study, a mean sitting diastolic blood pressure (SiDBP) > or = 95 and < or = 115 mm Hg was required. Patients received either 50-mg losartan once daily or 5-mg enalapril once daily at randomization. The dose of enalapril could be titrated to 10 mg after 4 weeks and 25 mg of HCTZ could be added after 8 weeks, based on measurements of SiDBP at clinic visits. The dose of losartan remained at 50 mg; 12.5 mg of HCTZ could be added after 8 weeks. Changes in the treatment regimen at each step were required if SiDBP remained > or = mm Hg. Doses of the diuretic were chosen based on commercially available forms of the test agents in combination with HCTZ. Trough blood pressure, heart rate, and safety parameters were measured at 4-week intervals during the treatment phase of the study. Significant reductions in mean SiDBP and mean sitting systolic blood pressure (SiSBP) were achieved at all time points (4, 8, and 12 weeks) with both treatments. No significant differences between treatment groups for mean changes in SiDBP or SiSBP were observed overall. At study end, patients receiving the losartan regimen had a mean reduction in SiDBP of 10.3 mm Hg, whereas patients in the enalapril regimen had a mean reduction of 9.8 mm Hg. Likewise, the percentage of patients reaching goal blood pressure reduction was not significantly different between groups. The mean reduction in SiDBP-- but not SiSBP--in black patients was slightly greater in the losartan group than in the enalapril group (SiDBP, 10.0 mm Hg losartan vs 8.0 mm Hg enalapril; P = 0.02). Similarly, losartan patients aged 65 years and older had a slightly greater decrease in SiDBP than comparable enalapril patients (12.7 mm Hg vs 8.7 mm Hg; P = 0.03). The importance of these differences between subgroups must be clarified by additional studies. Overall, both treatments were well tolerated. A regimen of losartan alone or in combination with HCTZ was effective in treating patients with essential hypertension and was comparable to a regimen of enalapril alone or in combination with HCTZ. However, treatment with losartan was associated with a lower incidence of cough.

Effect of low dose aspirin on cardiorenal function and acute hemodynamic response to enalaprilat in a canine model of severe heart failure

OBJECTIVES

This study examined the effect of low dose aspirin on cardiorenal and neurohumoral function and on the acute hemodynamic response to enalaprilat in a canine model of heart failure.

BACKGROUND

Low dose aspirin is frequently prescribed for patients with systolic dysfunction who also benefit from angiotensin-converting enzyme inhibition. Although high doses of potent cyclo-oxygenase inhibitors cause fluid retention and vaso-constriction and antagonize the effects of angiotensin-converting enzyme inhibitors, the effects of low dose aspirin in heart failure are unknown.

METHODS

A model of heart failure was produced in 11 mongrel dogs by rapid ventricular pacing (250 beats/min for 12 to 14 days). Five dogs received 325 mg aspirin/day for the final 4 days of pacing before the acute experiment; six control dogs received no aspirin. Cardiorenal and neurohumoral function was measured during chloralose anesthesia. Hemodynamic and renal responses to enalaprilat were assessed.

RESULTS

Both groups demonstrated severe heart failure with decreased cardiac output; increased atrial pressures and systemic resistance; activation of plasma renin activity, aldosterone and atrial natriuretic factor; and sodium retention. Low dose aspirin had no detrimental effect on cardiorenal or neurohumoral function. Mean arterial pressure, pulmonary capillary wedge pressure and systemic vascular resistance decreased to a similar degree with enalaprilat in both groups. There was no difference between the groups with respect to renal response to enalaprilat.

CONCLUSIONS

The present study demonstrates that low dose aspirin has no adverse effect on hemodynamic, neurohumoral or renal function in heart failure. Furthermore, aspirin has no adverse effect on the acute response to enalaprilat. These findings suggest that there is no contraindication to concomitant treatment with low dose aspirin and angiotensin-converting enzyme inhibitors in humans with heart failure.

Renal vascular responses to renin inhibition with zankiren in men

Renin inhibition represents an alternative to angiotensin-converting enzyme (ACE) inhibition for pharmacologic interruption of the renin-angiotensin system. In addition to inhibiting the formation of angiotensin II, ACE inhibitors also inhibit the degradation of kinin and result in accumulation of powerful renal vasodilator prostaglandins and bradykinin. We were therefore surprised by the large renal vasodilator response achieved with the renin inhibitor enalkiren, because substrate-specific renin inhibitors reduce the formation of angiotensin II without affecting other vasodilator mechanisms. To determine whether previous findings were reflective of the renin inhibitor class, we studied 12 healthy men on a sodium-restricted diet, each of whom received two or three escalating oral doses of zankiren, a new agent. Plasma renin activity decreased with the smallest dose (5 mg), and this effect was sustained. The increase in renal plasma flow was clearly related to dose (r = 0.86, F = 9.67), reaching a maximum of 134 +/- 26 ml/min/1.73 m2 at 250 mg, the highest dose. Renin inhibition exerts a remarkable renal vasodilator action, perhaps reflecting the lipophilicity of the agents developed to date, an action that may have clinical implications for the prevention of renal injury in patients at risk.

Captopril increases endothelin serum concentrations and preserves intestinal mucosa after mesenteric ischemia-reperfusion injury

Endothelial cells modulate the tone of the underlying smooth muscle by generating endothelium-derived relaxing and constricting factors. Captopril (CPT), unlike other angiotensin-converting enzyme (ACE) inhibitors, contains a sulfhydryl (-SH) group and can act as a free radical scavenger. Iloprost (ILO) is a synthetic analogue of prostacyclin and mimics the effects of this compound. This study was designed to investigate the effect of ILO and CPT on the mechanism of endothelin (ET) release after mesenteric ischemia-reperfusion (I/R) injury in the rat. Sprague-Dawley rats were divided into five groups: sham-operated, control, ILO (25 micrograms/kg), CPT (10 micrograms/kg), and ILO + CPT. The superior mesenteric artery was occluded for 30 min and then allowed 90 min of reperfusion, except in the sham-operated group, and the corresponding agents were given to the treated groups prior to I/R injury. After I/R injury, portal venous blood was obtained for ET assay, and ileal tissue samples were also obtained for the determination of malondialdehyde (MDA), prostaglandin E2 (PGE2) and leukotriene C4 (LTC4) and for histopathological examination. MDA levels were significantly lower in the CPT, ILO and, ILO + CPT groups than in the control group, indicating the inhibition of lipid peroxidation in all groups. ET levels increased in the control group, and this increase was reversed with ILO. In the CPT group, ET levels were significantly increased, and the addition of ILO did not affect this increase. Significant cytopreservative effect was achieved with ILO and CPT, the latter being more prominent histopathologically. CPT exerts a significant protective effect on the intestinal mucosa after I/R injury. This protection is accomplished by increased ET levels and seems to be unrelated to its inhibitory effect on lipid peroxidation and also unrelated to the arachidonic acid cascade.

Regression of left ventricular hypertrophy and improvement of renal hemodynamics in hypertensive patients treated with quinapril

Of 17 patients with mild to moderate essential hypertension, 8 showed echocardiographic evidence of left ventricular hypertrophy. Cardiac and renal function evaluated by glomerular filtration rate (GFR) were studied in all patients before and after 20 weeks of quinapril treatment. Systolic pressure decreased from 174.7 +/- 16.7 to 131.7 +/- 7.7 mmHg (p < .0001) and diastolic pressure decreased from 101.8 +/- 9.8 to 80 +/- 4.3 mmHg (p < .0001). Left ventricular mass index decreased in the eight patients with left ventricular hypertrophy (p < .01). Basal values of GFR were lower than normal in 41% of all patients; GFR increased significantly after 20 weeks of treatment (from 96.5 +/- 32.3 to 108.6 +/- 31.12 ml/min, p < .01); it decreased in only one patient. Patients reported few adverse effects to quinapril, and no important clinical laboratory abnormality was observed. Quinapril not only lowered arterial pressure, but it had a distinct effect on regression of left ventricular hypertrophy and favorable effects on renal function.

Participation of prostaglandins and bradykinin in the effects of angiotensin II and converting enzyme-inhibition on sympathetic neurotransmission in vivo

We investigated the mechanism(s) by which angiotensin converting enzyme (ACE)-inhibition and angiotensin (Ang) II influence peripheral sympathetic neurotransmission in canine gracilis muscle in situ, with alpha-adrenoceptors either intact or irreversibly blocked by phenoxybenzamine. ACE-inhibition by ramiprilat reduced, and subsequent infusion of Ang II (30 ng kg-1 min-1 i.v.) markedly increased arterial plasma Ang-(1-8)octapeptide levels, basal muscle perfusion pressures and mean arterial pressure. Local intra-arterial bolus injection of Ang II caused marked vasoconstriction followed by vasodilation. This vasoconstrictor response was enhanced and the ensuing vasodilation was abolished following prostaglandin synthesis inhibition by diclofenac. The vasoconstrictor response to low frequency (0.5 Hz) sympathetic nerve stimulation was also enhanced by diclofenac. The nerve stimulation-evoked noradrenaline (NA) overflow was reduced by ramiprilat when alpha-adrenoceptors were blocked (-11 +/- 3%, P < 0.05), but increased when alpha-adrenoceptors were intact (+28 +/- 14%, P < 0.05). During ACE-inhibition, effective bradykinin receptor antagonism by HOE 140 reduced stimulation-evoked NA overflow irrespective of alpha-adrenoceptor blockade (i.e. by 25 +/- 5 and 20 +/- 3% in the absence and presence of alpha-adrenoceptor blockade, respectively, P < 0.01). Diclofenac increased stimulation-evoked NA overflow in the absence of alpha-adrenoceptor blockade (+ 19 +/- 4%, P < 0.05). IV infusion of Ang II failed to enhance stimulation-evoked NA overflow both before and after diclofenac.(ABSTRACT TRUNCATED AT 250 WORDS)

Bradykinin is a mediator of anaphylactoid reactions during hemodialysis with AN69 membranes

Anaphylactoid reactions (AR) are the most feared complications of hemodialysis. Recently, a high incidence of AR has been reported during dialysis with AN69 membranes in patients treated with ACE inhibitors. Plasma levels of C3a, histamine and bradykinin were measured in 12 patients at the onset of AR during dialysis with AN69. We also investigated bradykinin generation in 10 symptom-free patients dialyzed with four different membranes. None of the 12 patients studied during AR displayed excessive complement activation or histamine release. In contrast, high bradykinin plasma levels (2392 +/- 53 fmol/ml; mean +/- SEM) were observed in all nine patients of whom bradykinin was measured. One patient developed two consecutive episodes of hypersensitivity on AN69 membranes even without taking ACE inhibitors. Bradykinin levels were high in both episodes (5280 and 10467.7 fmol/ml). Furthermore, this patient showed no symptoms and normal bradykinin levels (123.4 fmol/ml) when dialyzed with other membranes. The role of the membrane type in the AR is further substantiated by the observation that AN69 also provoked a significantly higher bradykinin generation (327.6 +/- 18 fmol/ml; mean +/- SEM) during symptom-free sessions compared to other membranes like CuprophanR (5.1 +/- 7.3), HemophanR (17.2 +/- 6.3) and PolysulfoneR (39.7 +/- 6.6). Our findings strongly suggest that bradykinin is the principal mediator of AR during hemodialysis with AN69 membranes. To our knowledge it is the first time that data support the hypothesis of a more general role of bradykinin in shock-like symptoms. Furthermore, bradykinin generation must be regarded as a new marker of biocompatibility of extracorporeal treatments.

Renal and hormonal responses to repeated treatment with enalapril in non-azotemic cirrhosis with ascites

Since a single dose of the angiotensin-converting enzyme inhibitor enalapril was shown to cause natriuresis in cirrhosis in a previous study, we investigated whether repeated doses of this substance would sustain a favorable renal effect in cirrhosis. Ten milligrams of enalapril maleate were administered once a day for 8 days to ten patients with non-azotemic cirrhosis and ascites. Enalapril reduced blood pressure significantly at 4 to 12 h (systolic blood pressure) and 2, 6, and 8 h (diastolic blood pressure) on day 2, compared to pretreatment (day 0) values, but this depressor effect decreased on day 8. No change in heart rate could be detected. Enalapril significantly suppressed serum angiotensin-converting enzyme activity and plasma aldosterone concentration (p < 0.001 to 0.01), which were elevated prior to treatment, with pretreatment values of 25.8 +/- 1.8 IU/l for serum angiotensin-converting enzyme activity and 241 +/- 67 pg/ml for plasma aldosterone concentration. This drug caused a 12 to 24% increase (p < 0.05 to 0.01) in mean daily urinary volume and a 40 to 54% increase (p < 0.001 to 0.01) in mean daily urinary sodium excretion from the respective pretreatment baselines during the 8-day period. Creatinine clearance was improved (p < 0.05) by the treatment, with mean improvement values from 24 to 34% above the pretreatment value of 47.4 +/- 4.3 ml/min.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses to converting enzyme and renin inhibition. Role of angiotensin II in humans

We compared the renal vascular responses to angiotensin converting enzyme inhibition and renin inhibition to assess the influence of angiotensin II (Ang II). We examined the renal and endocrine responses to the renin inhibitor enalkiren, to captopril, and to placebo in nine healthy and nine hypertensive men on a 10-mmol sodium diet. Ang II was infused to assess effects of the agents on renal and adrenal responsiveness to Ang II. Plasma Ang II concentration was suppressed similarly with enalkiren and captopril--an identical level of blockade was achieved. Although renal plasma flow was stable during placebo, a substantial rise was seen with both enalkiren (+133 +/- 26 mL/min per 1.73 m2) and captopril (+99.4 +/- 22.6). There was remarkable intrasubject concordance between the renal plasma flow responses to renin inhibition and converting enzyme inhibition (r = .90, P < .004). The vasodilator response to both agents correlated inversely with the fall in renal plasma flow induced by Ang II alone (r = -.66, P < .05). Both agents significantly enhanced the renal vascular response to Ang II (P = .01), and, furthermore, the renal vasodilator response to captopril predicted the potentiation of the renal plasma flow response to Ang II after either agent (enalkiren: r = .91, P < .001; captopril: r = .56, P < .05). Concordance of the maximal renal plasma flow response to the two agents appeared in the hypertensive men as well. Our results indicate that the acute renal response to captopril largely reflects a reduction in Ang II formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-converting enzyme inhibitors: more different than alike? Focus on cardiac performance

Development of an increased systemic vascular resistance and the concomitant increase in blood pressure are associated with significant changes in left ventricular structure and function. The plasma and tissue renin-angiotensin systems play an important, but variable, role in the regulation of blood pressure and systemic vascular resistance in normotensive and hypertensive patients. Non-angiotensin-mediated effects of angiotensin-converting enzyme (ACE) inhibitors and/or differential tissue specificities may result in a variable hemodynamic response to individual therapies. Using first-pass radionuclide cineangiography, the hemodynamic effects of captopril, lisinopril, and fosinopril were compared. Fosinopril induced a greater reduction in systemic vascular resistance than did equipotent hypotensive doses of captopril or lisinopril and was associated with an increase in cardiac output, left ventricular peak ejection rate, and left ventricular peak filling rate. Along with previously accumulated data, these results suggest that structural differences among ACE inhibitors may result in unique physiologic effects. Fosinopril appears to have a cardiotropic effect that causes improved left ventricular diastolic performance; this effect is unique among currently available ACE inhibitors. The clinical significance of the unique profiles of individual ACE inhibitors awaits assessment via comparative clinical investigations.

Post-exercise reduction in blood pressure in hypertensive subjects: effects of angiotensin converting enzyme inhibition

1. Much attention has been given to the effects of various classes of antihypertensive drugs on blood pressure and haemodynamics. The effects of a single bout of exercise on post-exercise blood pressure have also been studied by several investigators. However, the combined effects of prior exercise and antihypertensive medication has drawn less attention. 2. We examined the separate and combined effects of a single bout of exercise and of angiotensin converting enzyme (ACE) inhibition with a new ACE inhibitor (fosinopril, 20 mg day(-1)) on post-exercise blood pressure and systemic and regional haemodynamics. Ten patients with mild-to-moderate hypertension were studied with a double-blind, randomized crossover, placebo- and rest period-controlled study design. 3. At rest, mean arterial pressure (MAP, -10 +/- 2 mm Hg), total peripheral resistance (TPR, -11 +/- 5%) and forearm vascular resistance (FVR, -17 +/- 8%) were significantly (P < 0.05) reduced during ACE inhibition as compared with the placebo phase. 4. During the placebo phase, MAP (-3 +/- 1 mm Hg), TPR (-10 +/- 4%) and FVR (-9 +/- 4%) were lower after exercise as compared with the control rest period. 5. During ACE inhibition, MAP (-3 +/- 1 mm Hg) and TPR (-8 +/- 4%) were lower, but FVR (+32 +/- 15%) was increased after exercise as compared with the control rest period. 6. Thus, blood pressure and TPR decreased similarly after exercise during the placebo phase and during ACE inhibition. However, differences in post-exercise forearm haemodynamics during the placebo phase and during ACE inhibition indicate that underlying regional haemodynamics are modified.

Salt-dependent renal effects of an angiotensin II antagonist in healthy subjects

This study was designed to evaluate in healthy volunteers the renal hemodynamic and tubular effects of the orally active angiotensin II receptor antagonist losartan (DuP 753 or MK 954). Losartan or a placebo was administered to 23 subjects maintained on a high-sodium (200 mmol/d) or a low-sodium (50 mmol/d) diet in a randomized, double-blind, crossover study. The two 6-day diet periods were separated by a 5-day washout period. On day 6, the subjects were water loaded, and blood pressure, renal hemodynamics, and urinary electrolyte excretion were measured for 6 hours after a single 100-mg oral dose of losartan (n = 16) or placebo (n = 7). Losartan induced no significant changes in blood pressure, glomerular filtration rate, or renal blood flow in these water-loaded subjects, whatever the sodium diet. In subjects on a low-salt diet, losartan markedly increased urinary sodium excretion from 115 +/- 9 to 207 +/- 21 mumol/min (P < .05). The fractional excretion of endogenous lithium was unchanged, suggesting no effect of losartan on the early proximal tubule in our experimental conditions. Losartan also increased urine flow rate (from 10.5 +/- 0.4 to 13.1 +/- 0.6 mL/min, P < .05); urinary potassium excretion (from 117 +/- 6.9 to 155 +/- 11 mumol/min); and the excretion of chloride, magnesium, calcium, and phosphate. In subjects on a high-salt diet, similar effects of losartan were observed, but the changes induced by the angiotensin II antagonist did not reach statistical significance. In addition, losartan demonstrated significant uricosuric properties with both sodium diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Bradykinin causes selective efferent arteriolar dilation during angiotensin I converting enzyme inhibition

We studied the effects of interruption of the renin-angiotensin system (RAS) in rats that were volume depleted by water deprivation for 48 hours (AWD) with/without furosemide (AWD + F), a condition known to activate RAS. Following baseline micropuncture, AWD rats (N = 6) were treated with a specific angiotensin II type 1 receptor antagonist (AIIRA; 4 mg/kg body wt bolus i.v. and then continuous infusion) and glomerular hemodynamics compared to those obtained during angiotensin I converting enzyme inhibitor treatment (ACEI; 24 mg/kg bolus i.v. and then continuous infusion). Systemic blood pressure decreased equally following AIIRA and ACEI. Single nephron glomerular filtration rate (SNGFR) increased from baseline following AIIRA (24 nl/min vs. 30, P < 0.025). While a decrease in efferent arteriolar resistance (RE) reduced glomerular capillary pressure (PGC; 67 mm Hg vs. 60, P < 0.05), this change in RE together with decrease in afferent arteriolar resistance (RA), enhanced glomerular plasma flow rate (QA; 80 nl/min vs. 111). Antagonizing angiotensin II receptor increased QA which, together with the tendency to increase glomerular capillary ultrafiltration coefficient, Kf, served to improve glomerular filtration. By contrast, although inhibition of the angiotensin I converting enzyme caused greater vasodilatation, no increase in SNGFR occurred. The lack of response in filtration after ACEI was due to a further fall in PGC to 52 mm Hg (P < 0.01 vs. AIIRA), reflecting profound reduction in RE. Since ACEI but not AIIRA potentiates bradykinin activity we examined effects of a specific bradykinin antagonist (Hoe).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of somatostatin and captopril on glomerular prostaglandin E2 production in normal and diabetic rats

Somatostatin (SRIH) has recently been shown to be effective in reversing many of the early changes of diabetic nephropathy. It is unknown whether SRIH exerts its protective effects via its ability to suppress growth hormone (GH) or via other direct renal effects. Since changes in glomerular prostaglandin (PG) E2 production are thought to be an important part of the underlying pathophysiology of diabetic nephropathy, we sought to determine if SRIH altered glomerular PG E2 production in the rat. Whole glomeruli isolated from streptozotocin-diabetic rats and from controls were incubated with either saline, captopril, or varying concentrations of SRIH, and PG E2 production was determined by direct radioimmunoassay of media. Incubation with captopril (10(-4) M) resulted in equivalent increases in PG E2 production in glomeruli from both control and diabetic rats (140.8 +/- 12.8% and 150.2 +/- 18.9% respectively). Incubation with high concentrations of SRIH (10(-6) M) also resulted in significant increases in glomerular PG E2 production in both diabetic and control rats. However, at low SRIH concentrations (10(-10) M), glomerular PG E2 production was increased only in the diabetic rats (167.0 +/- 11.4% vs 95.3 +/- 9.2% in normals). We conclude that SRIH increases glomerular PG E2 production, and that glomeruli from diabetic rats appear to be more sensitive to lower concentrations of SRIH when compared to normal rats. It is possible that this effect on PG E2 production may underlie the favorable effects of SRIH on the glomerulus in diabetes.

Effects of EXP3174, a non-peptide angiotensin II receptor antagonist, on renal hemodynamics and renal function in dogs

We examined the effects of intrarenal infusion of EXP3174, a non-peptide angiotensin II receptor antagonist, in order to evaluate the physiological role of endogenous angiotensin II in regulating renal hemodynamics and urine formation and to assess the possibility of a tubular site(s) of action of endogenous angiotensin II in anesthetized dogs. Intrarenal infusion of EXP3174 at 15 micrograms/kg per min caused increases in renal blood flow (RBF), glomerular filtration rate (GFR), urine, flow and urinary electrolyte excretion. The lower dose of EXP3174 (0.5 micrograms/kg per min) did not change mean arterial pressure, RBF and GFR, but did increase urine flow. The fractional excretion of sodium, the fractional proximal excretion of sodium and the fractional distal excretion of sodium increased with lower doses of EXP3174 infusion. EXP3174 did not affect the linear relationship between the free water reabsorption rate and osmolar clearance. These data suggest that endogenous angiotensin II plays a significant role in regulating renal hemodynamics and urine formation and endogenous angiotensin II stimulates sodium reabsorption in the proximal and the distal portions of the tubules, with the exception of the medullary portion of the ascending limb of Henle.

Newer concepts in the medical management of patients with congestive heart failure

Congestive heart failure (CHF) remains a major cause of morbidity and mortality in the United States, especially among the elderly. Although an underlying disturbance in cardiac function can be identified in most patients, manifestations of the disease are greatly influenced by other factors, particularly neurohumoral and peripheral adaptive responses which occur secondary to impaired cardiac function. The renin-angiotensin system (RAS) is integrally involved in the pathophysiology of CHF. Originally considered a humoral system, the RAS is now known to exist and operate within cardiac and vascular tissues. The importance of tissue-specific renin-angiotensin systems in CHF is presently under investigation. Most patients with symptomatic CHF benefit from the administration of an ACE inhibitor. Certain asymptomatic patients, such as those with severe left ventricular (LV) dysfunction and those who are at high risk for LV remodeling after anterior wall myocardial infarction, may also benefit from ACE inhibitor therapy. Diuretics and nitrates improve symptoms and often cardiac output in many patients with CHF. Although many new inotropic agents have been tested in CHF patients, none appear clinically superior to digitalis glycosides. The efficacy of digitalis glycosides in CHF may in part result from sympathoinhibitory properties such as the activation of baroreceptor mechanisms. Despite the fact that many CHF patients die from arrhythmias, treatment of asymptomatic ventricular arrhythmias in these patients is not recommended. Patients with symptomatic or sustained ventricular arrhythmias are best treated by a physician experienced in cardiac electrophysiology. Therapy with beta-blocking drugs for CHF patients is controversial. Anticoagulants are recommended for selected patients with CHF. Finally, exercise therapy may improve functional capacity in some patients with CHF through its effects on peripheral blood vessels and skeletal muscle tissues.

Differences in structure of angiotensin-converting enzyme inhibitors might predict differences in action

Angiotensin-converting enzyme (ACE) inhibitors probably work by inhibition of tissue-located ACE, and they differ with regard to their relative ability to inhibit ACE in different organs. This apparent tissue selectivity may stem from either differences in tissue bioavailability or from a different affinity for the enzyme. The affinity of the ACE inhibitor for a particular enzyme is not only determined by the structure of the inhibitor, but also by the structure of the enzyme. ACE enzymes from different tissues may be slightly different, and this may have some bearing on the relative affinities of different ACE inhibitors for ACE from different tissues. The duration of inhibition in a particular tissue reflects not only the affinity of that inhibitor for the tissue enzyme, but also reflects the ease or difficulty with which the active ACE inhibitor is released from that tissue. Whether the beneficial effects of ACE inhibitors on experimentally induced myocardial infarction and reperfusion arrhythmias are due to the presence of a sulfhydryl group or are mainly related to the ACE inhibitor-mediated bradykinin potentiation remains a matter of controversy.

Influence of angiotensin II, alpha- and beta-adrenoceptors on peripheral noradrenergic neurotransmission in canine gracilis muscle in vivo

Interactions between angiotensin II and adrenoceptor-mediated effects on peripheral sympathetic neurotransmission were investigated in constant flow blood-perfused canine gracilis muscle in situ, without and with pretreatment by non-competitive alpha-adrenoceptor blockade. Angiotensin converting enzyme (ACE)-inhibition by benazeprilat increased nerve stimulation (2 Hz, 4 min)-evoked noradrenaline (NA) overflow (+ 21 +/- 5%) with alpha-adrenoceptors intact, but reduced NA overflow (- 18 +/- 6%) when alpha-adrenoceptors were blocked. Vasoconstrictor responses were slightly reduced by benazeprilat. Subsequent infusion of angiotensin II (Ang II, 20 and 500 ng kg-1 min-1 i.v., raising arterial concentrations from 0.6 +/- 0.2 pM to 1390 +/- 240 and 25,110 +/- 3980 pM, respectively) failed to increase NA overflow or to enhance stimulation-evoked vasoconstriction. Adrenaline (0.4 nmol kg-1 min-1 i.v.) did not change evoked NA overflow before or after benazeprilat, either with or without alpha-adrenoceptor blockade, despite high concentrations (approximately 10 nM) in arterial plasma. Following benazeprilat, propranolol reduced NA overflow (- 24 +/- 3%) only if the alpha-adrenoceptors were blocked. In conclusion, benazeprilat reduced evoked NA overflow in the presence of alpha-adrenoceptor blockade to a similar degree as previously shown in the presence of neuronal uptake inhibition in this model. However, contrasting to our previous findings, benazeprilat enhanced NA overflow and reduced the post-junctional response to nerve stimulation in the absence of alpha-adrenoceptor blockade. This could be related to bradykinin accumulation during ACE-inhibition, in addition to the reduction of Ang II generation. Our data are not compatible with facilitation of NA release by circulating Ang II even at pharmacological dose levels. Although activation of prejunctional beta-adrenoceptors may facilitate evoked NA overflow in this model, circulating adrenaline is ineffective under physiological conditions even after alpha-adrenoceptor blockade. Also, beta-adrenoceptor-mediated prejunctional effects do not seem to involve Ang II in canine skeletal muscle in vivo.