Specificity of renal vasodilation with captopril: Saralasin prevents the response in the doca-treated,salt-loaded rabbit

A prominent action of converting enzyme inhibitors, such as captopril, is a reduction in angiotensin II formation, but interpretation of responses has been complicated by the potential for such agents to reduce bradykinin degradation and promote prostaglandin release. To assess the specificity of the action of captopril, we pretreated rabbits with desoxycorticosterone and a high sodium intake, to suppress the renin-angiotensin system and thus maximize the renal vascular responses which might be unrelated to angiotensin II. Captopril was infused intravenously in graded dosage from 10 to 3,000 μg/kg, and renal blood flow measured with an electromagnetic flowmeter. Despite suppression of the renin system, captopril increased renal blood flow from 3.7 ± 0.5 to 5.3 ± 0.8 ml/g/min (p < .001) in 7 rabbits. In 6 additional rabbits, captopril was superimposed on a saralasin infusion (1.0 μg/kg/min) in a dose sufficient to block responses to endogenous angiotensin II. Saralasin prevented entirely the renal vasodilator response to captopril. Two surprising conclusions derive from this study: first, the renal vasodilator response to captopril appears to be specific for a reduction in angiotensin II formation; second, endogenous angiotensin appears to contribute to renal vascular tone, at least when anesthesia is employed, even when the renin system has been suppressed by a combination of a high sodium intake and desoxycorticosterone.     

Effect of captopril on kidney function in insulin-dependent diabetic patients with nephropathy.

The influence of angiotensin II on kidney function in diabetic nephropathy was assessed by studying the effect of 12 weeks'' monotherapy with captopril (25-50 mg twice a day) in 16 hypertensive insulin dependent diabetic patients with persistent albuminuria. In an initial one week randomised single blind trial of captopril versus placebo, captopril (for nine patients) reduced arterial blood pressure from 148/94 (SD11/6) to 135/88 (8/7) mm Hg (p less than 0.05) and albuminuria from 1549 (range 352-2238) to 1170 (297-2198) micrograms/min (p less than 0.05), while glomerular filtration rate remained stable. No significant changes occurred in seven patients treated with placebo. During the 12 weeks of captopril treatment arterial blood pressure in all patients fell from 147/94 (11/6) to 135/86 (13/7) mm Hg (p less than 0.01), albuminuria fell from 1589 (range 168-2588) to 1075 (35-2647) micrograms/min (p less than 0.01), and glomerular filtration rate fell from 99 (SD19) to 93 (25) ml/min/1.73 m2 (p less than 0.01). The renin-angiotensin system showed suppressed plasma concentrations of angiotensin II and increased concentrations of angiotensin I and renin. The study showed that glomerular filtration rate is not dependent on angiotensin II, that captopril reduces albuminuria, probably by lowering glomerular hypertension, and that captopril represents a valuable new drug for treating hypertension in diabetics dependent on insulin with nephropathy.     

Captopril treatment induces hyperplasia but inhibits myonuclear accretion following severe myotrauma in murine skeletal muscle

The role of ANG II in skeletal muscle and satellite cell regulation is largely unknown. Cardiotoxin (CTX) was used to investigate whether muscle injury activates a local ANG II signaling system. Following injury, immunohistochelmistry (IHC) analysis revealed a robust increase in the intensity of angiotensinogen and angiotensin type 1 (AT(1)) receptor expression. As regeneration proceeded, however, AT(1) and angiotensinogen were downregulated. Nuclear accretion and fiber formation were also assessed during muscle regeneration in mice treated with captopril (an angiotensin-converting enzyme inhibitor). When ANG II formation was blocked through the use of captopril, we observed a significantly reduced accretion of nuclei into myofibers (-25%), while tibialis anterior total fiber number was significantly increased +37%. This phenotype appeared to be due to alterations in satellite cell differentiation kinetics; captopril treatment led to sustained mRNA expression of markers associated with quiescence and proliferation (Myf5, Pax7) and simultaneously delayed or inhibited the expression of myogenin. IHC staining supported these findings, revealing that captopril treatment resulted in a strong trend (P = 0.06) for a decrease in the proportion of myogenin-positive myoblasts. Furthermore, these observations were associated with a delay in muscle fiber maturation; captopril treatment resulted in sustained expression of embryonic myosin heavy chain. Collectively, these findings demonstrate that localized skeletal muscle angiotensin signaling is important to muscle fiber formation, myonuclear accretion, and satellite cell function.     

Direct evidence for local generation and release of angiotensin II in human vascular tissue

A direct measurement of both angiotensins I and II immunoreactive substances was made in the perfusate from isolated human umbilical vein perfused with Krebs-Ringer solution which was free of any component of the renin-angiotensin system. The identity of the immunoreactive peptides was confirmed as angiotensin I and angiotensin II by high-performance liquid chromatography in reference to standard compounds. The rate of release of angiotensins was 41.9 +/- 7.4 and 63.4 +/- 12.0 pg for angiotensins I and II, respectively, during the first perfusion period of 30 min, and it remained stable at least for 3 hours. Angiotensin-converting enzyme inhibitor captopril, added to the perfusion medium (10(-9) to 5 x 10(-6) M), suppressed immunoreactive angiotensin II release in a dose-dependent fashion; the maximal percent inhibition of angiotensin II release evoked by captopril (5 x 10(-6) M) was approximately 56%. These results taken together with the previous observations of presence of essential components of the renin-angiotensin system in vascular tissue provide direct evidence for local generation and subsequent release of angiotensin II in vascular beds of human beings.     

Captopril in renovascular hypertension: long-term use in predicting surgical outcome.

The angiotensin converting-enzyme inhibitor captopril was used as long-term preoperative treatment in a series of hypertensive patients with unilateral renal arterial disease. There were immediate and sustained falls in plasma angiotensin II and aldosterone concentrations, with converse increases in circulating renin and angiotensin I. In patients with sodium and potassium deficiency and secondary aldosterone excess before treatment captopril corrected the sodium and potassium deficits; in these cases the initial hypotensive response was profound but the later effect was less pronounced. When sodium and potassium state was initially normal it remained unchanged during captopril treatment, while the full hypotensive effect took up to three weeks to be attained. The immediate, but not long-term, falls in arterial pressure with captopril were proportional to the immediate decrements of plasma angiotensin II. Nevertheless, while the immediate blood-pressure reduction with captopril variously overestimated and underestimated the eventual surgical response, the absolute blood-pressure values during long-term captopril related well with those after operation. Pretreatment plasma renin and angiotensin II concentrations, while closely predicting the immediate captopril response, are fallible guides to surgical prognosis. In contrast, long-term treatment with converting-enzyme inhibitors may provide an accurate indication of surgical outcome.     

Circulating angiotensins in the river lamprey, Lampetra fluviatilis, acclimated to freshwater and seawater: possible involvement in the regulation of drinking

Plasma angiotensin levels were measured for the first time in a cyclostome, the river lamprey. With the demonstration that angiotensins are present in the circulation, the possibility of a physiological role in the regulation of drinking was re-examined. Angiotensin II and III concentrations and plasma osmolalities were significantly higher in lampreys acclimated to 28 ppt seawater than in those acclimated to freshwater. No changes were found in angiotensin II and III levels 4 h after transfer from freshwater to 50% seawater, although plasma osmolality had started to rise by this time. There was a suggestion that plasma angiotensin II levels might be related to osmolality in the transfer experiment. Injection of Asp(1)Val(5)- or Asn(1)Val(5)-angiotensin II (40-169 microg/kg body wt.) did not stimulate drinking in freshwater-acclimated lampreys, even when they were still capable of drinking. The angiotensin-converting enzyme inhibitor captopril and the smooth muscle relaxant papaverine both reduced drinking rate in 50% seawater-acclimated lampreys. The data do not provide direct evidence for the involvement of the renin-angiotensin system in the control of drinking behaviour in the lamprey. Indirect evidence from the captopril effect is suggestive, but could have other explanations.     

Activation and suppression of renin-angiotensin system in human dendritic cells

We previously identified the gene expression of renin-angiotensin system in human monocyte-derived dendritic cells (DCs). This study was conducted to examine the mechanisms by which angiotensin II and captopril, the inhibitor of the angiotensin-converting enzyme (ACE), affect human DCs. In DCs, lipopolysaccharide (LPS)-induced production of tumor necrosis factor-alpha (TNF-alpha), interleukin-(IL)-1alpha, IL-10, IL-12, and IL-18 was significantly inhibited by captopril. In contrast, angiotensin II treatment resulted in a significant increase in TNF-alpha and IL-6 protein biosynthesis by DCs. In addition, we have studied the global expression of 2400 genes in DCs from two donors. Here, we demonstrated the specific down-regulation of the ACE gene expression in captopril-treated DCs. Our finding indicates the possible activation of NF-kappaB through the up-regulation of expressions of MEFV gene (encoding PYRIN protein) and heterogeneous nuclear ribonucleoprotein R in DCs. This is the first study on the modulation of cytokine and gene expression by angiotensin II and captopril in DCs.     

Effect of the arterial hypertension and captopril treatment on the angiotensin II content in the subfornical organ. A study in SHR rats

We studied the effects of spontaneous high blood pressure and the captopril treatment on the subfornical organ (SFO) of rats. The brains of control Wistar-Kyoto rats (WKY), WKY rats treated with captopril (WKY-T), spontaneously hypertensive rats (SHR) and SHR rats treated with captopril (SHR-T) were processed immunohistochemically using anti-angiotensin II as primary antibody. Immunorective material (IRM) for angiotensin II was observed in a group of neurons and some cells of the ependymal layer of the SFO in WKY rats. The angiotensin II immunoreactive (AGII-ir) in the SHR rats was decreased, showing positive reaction only in a few neurons, while captopril treatment induced an increase in immunoreactive material in hypertensive rats, but contrarily, the expression of AGII-ir in the WKY-T group was scarce. The variations of the angiotensin II observed in the SFO could be owing to an interaction between the hypertension and its captopril treatment.     

The involvement of angiotensins in the control of prostatic epithelial cell proliferation in the rat.

The effects of captopril (the inhibitor of the angiotensin-converting enzyme) and of angiotensins II and IV (3-8 fragment of angiotensin II) on cell proliferation of the prostatic epithelium was investigated in the rat. The incorporation of bromodeoxyuridine into cell nuclei was used as an index of cell proliferation. It was found that the treatment with captopril resulted in the suppression of prostatic epithelial cell proliferation. The antiproliferative effect of captopril was reversed (at least partially) by a simultaneous treatment with either angiotensin II or angiotensin IV. The effects of angiotensins were not blocked by the administration of losartan--AT1 angiotensin receptor blocker. These findings suggest the involvement of angiotensins in the control of prostatic growth, acting via the receptors different from the AT1-subtype (presumably via AT4 receptors).     

Captopril attenuates reflex adrenergic response in essential hypertension

An attenuation of adrenergic activity during the inhibition of endogenous angiotensin II formation was evaluated by determining plasma norepinephrine concentration after a single oral administration of captopril compared to that after nifedipine in essential hypertension. Captopril produced a fall in mean arterial pressure (-24 +/- 2 mmHg, p less than 0.01) which magnitude was the same as that gained by nifedipine (-22 +/- 3 mmHg, p less than 0.01). Reflex tachycardia due to hypotension was produced (+13 +/- 1 beats/min, p less than 0.01) after nifedipine but not after captopril (-1 +/- 2 beats/min, p greater than 0.05). Although the enhancement of plasma renin activity induced by captopril (+1.54 +/- 0.56 ng/ml/hr, p less than 0.05) was similar (p greater than 0.05) to that by nifedipine (+1.44 +/- 0.47 ng/ml/hr, p less than 0.05), plasma norepinephrine concentration increased less (p less than 0.01) after captopril (+100 +/- 23 ng/ml, p less than 0.05) than after nifedipine (+283 +/- 51 ng/ml, p less than 0.05). Thus, the diminished adrenergic activity is a likely candidate for the abolished reflex tachycardia after the inhibition of angiotensin I converting enzyme activity by captopril in essential hypertension.     

Differential prejunctional effect of captopril and saralasin on neurogenic vasoconstriction in pithed normotensive rats

The present study describes a differential inhibitory effect of captopril and [Sar1 Ala8]angiotensin II (saralasin) on the neurogenic vasoconstriction in pithed normotensive rats. In pithed normotensive rats with intact kidneys captopril more profoundly inhibited the vasopressor response to spinal stimulation than observed for saralasin. Bilateral nephrectomy also diminished the hypertensive response to spinal stimulation. After bilateral nephrectomy, 1 h previously, captopril but not saralasin diminished the hypertensive response to spinal stimulation. After bilateral nephrectomy, 18-24 h previously, captopril did not produce an additional reduction of the vasopressor response to spinal stimulation. In contrast, saralasin significantly potentiated the neurogenic vasoconstriction. The results suggest that both captopril and saralasin diminish the hypertensive response to spinal stimulation by producing dilatation of vascular smooth muscle in pithed normotensive rats. Apart from this common mechanism, a differential effect of captopril and saralasin on the neurogenic vasoconstriction can be observed. In contrast to saralasin, captopril may depress the neurogenic vasoconstriction in pithed normotensive rats by blocking the sympathofacilitatory action induced by subpressor levels of angiotensin II (AII). In pithed normotensive rats, saralasin may mimic the sympathofacilitatory action of subpressor AII.     

Angiotensin-converting enzyme inhibition reduces neuroblastoma cell growth rate

Because of the known capacity of angiotensin II to serve as a growth factor in multiple tissues, we elected to study the effects of renin-angiotensin system inhibition on the growth of human SH-SY5Y neuroblastoma cells. Cells were treated with captopril (0.05-5 mg/ml), enalapril, or enalaprilat (0.02-5 mg/ml) or saralasin (0.1-0.25 mg/ml). In all cases, statistically significant reductions in cell growth were seen over 5 days of culture. In additional experiments, captopril and enalaprilat significantly decreased thymidine incorporation into DNA in these cells. The administration of angiotensin II in the presence of captopril partially offset these suppressive effects.     

Effects of angiotensin II on pressor responses to norepinephrine in humans

In previous studies in the conscious rabbit and in isolated artery preparations, low doses of angiotensin II synergistically amplified the pressor effects of the sympathetic neurotransmitter, norepinephrine (NE). To determine whether these observations could be replicated in humans, 9 normal adult male volunteers (mean age: 34) each were given 3 i.v. doses of NE (25, 50 and 100 micrograms.kg-1.min-1) during consecutive 10 min infusion periods. On a second study day, the procedure was repeated during infusion of angiotensin II in a subpressor dose (1.25 ng.kg-1.min-1). The angiotensin II didn't alter the BP responses to NE, but it attenuated the heart rate (HR) decreases associated with the NE infusions by 80% (P less than 0.05), 42% (P less than 0.05) and 42% (P less than 0.1). The two study days were then repeated following 2 weeks of oral treatment with the angiotensin converting enzyme inhibitor captopril (which, despite significantly decreasing baseline BP, also tended to decrease HR). In the presence of captopril, the pressor responses to the NE challenges were reduced by 50% (P less than 0.05), 33% (P less than 0.05) and 13% (P less than 0.1) compared with the pre-captopril responses. Thus, angiotensin II in subpressor doses appears to enhance NE pressor effects by attenuating the compensatory HR responses, whereas inhibition of endogenous angiotensin II mechanisms weakens the BP-raising actions of NE. These findings in humans are consistent with earlier observations that the renin-angiotensin system can directly amplify sympathetic pressor effects in two separate ways: by modifying baroreceptor sensitivity and by enhancing the actions of norepinephrine on vascular smooth muscle.     

Enzymatic formation of angiotensins II and III in the hindlimb circulation of dogs

Experiments were performed in 14 anesthetized dogs to (1) to determine if the reductions in hindlimb blood flow produced by [des-Asp1] angiotensin I were due to its local enzymatic (kininase II) conversion to angiotensin III and (2) to quantitate the extent of conversion of angiotensin I to angiotensin II and of [des-Asp1] angiotensin I to angiotensin III in the hindlimb circulation. Graded doses of these peptides were administered as bolus injections directly into the left external iliac artery while measuring flow in this artery electromagnetically. Dose-response relationships were determined before and during the inhibition of kininase II activity with captopril or antagonism of angiotensin receptor sites with [Ile7] angiotensin III. Captopril inhibited the vasoconstrictor responses to angiotensin I and [des-Asp1] angiotensin I, but did not affect the responses to angiotensins II or III, or norepinephrine. [Ile7] angiotensin III inhibited the vasoconstrictor responses to all four angiotensin peptides but did not alter the responses to norepinephrine. These findings indicate that the hindlimb vasoconstrictor responses to [des-Asp1] angiotensin I were due to the local formation of angiotensin III. The extent of conversion of [des-Asp1] angiotensin I to angiotensin III that occurred in one transit through the hindlimb arterial circulation was estimated to be 36.7%, which was not different from the estimated 36.4% conversion of angiotensin I to angiotensin II. We conclude that angiotensin I and [des-Asp1] angiotensin I are converted to their respective vasoactive forms (angiotensins II and III) to a similar extent in the hindlimb circulation via the action of kininase II.     

Hormonal and renal responses to converting enzyme inhibition during maximal exercise

The role of angiotensin II in the hormonal and renal responses to maximal exercise was investigated by using the angiotensin-converting enzyme inhibitor captopril. Nine male subjects performed a standardized maximal treadmill test with and without acute captopril treatment (25 mg orally). At rest, captopril elevated plasma renin activity and lowered aldosterone levels. With maximal exercise, captopril treatment reduced the increase in mean arterial blood pressure by 8 mmHg and the increase in plasma renin activity by 3.0 ng ANG I.ml-1.h-1. The responses of adrenocorticotropin (ACTH), cortisol, and vasopressin to maximal exercise were not altered by captopril treatment. Although aldosterone levels were reduced at rest with captopril, during maximal exercise no difference was noted between treatments. Captopril treatment had no effects on the renal handling of salts or water during exercise. In conclusion, angiotensin II plays a role in the increase in mean blood pressure during maximal exercise in normal subjects but has no effect on the exercise responses of ACTH, vasopressin, and aldosterone or on the renal handling of salts and water.     

The role of the renin-angiotensin system and oxidative stress in spontaneously hypertensive rat mesenteric collateral growth impairment

Recent clinical and animal studies have shown that collateral artery growth is impaired in the presence of vascular risk factors, including hypertension. Available evidence suggests that angiotensin-converting enzyme inhibitors (ACEI) promote collateral growth in both hypertensive humans and animals; however, the specific mechanisms are not established. This study evaluated the hypothesis that collateral growth impairment in hypertension is mediated by excess superoxide produced by NAD(P)H oxidase in response to stimulation of the ANG II type 1 receptor. After ileal artery ligation, mesenteric collateral growth did not occur in untreated, young, spontaneously hypertensive rats. Significant luminal expansion occurred in collaterals of spontaneously hypertensive rats treated with the superoxide dismutase mimetic tempol, the NAD(P)H oxidase inhibitor apocynin, and the ACEI captopril, but not ANG II type 1 (losartan) or type 2 (PD-123319) receptor blockers. The ACEI enalapril produced equivalent reduction of arterial pressure as captopril but did not promote luminal expansion. This suggests the effects of captopril on collateral growth might result from its antioxidant properties. RT-PCR demonstrated that ANG II type 1 receptor and angiotensinogen expression was reduced in collaterals of untreated rats. This local suppression of the renin angiotensin system provides a potential explanation for the lack of effect of enalapril and losartan on collateral growth. The results demonstrate the capability of antioxidant therapies, including captopril, to reverse impaired collateral artery growth and the novel finding that components of the local renin angiotensin system are naturally suppressed in collaterals.     

Effects of various doses of captopril on plasma aldosterone concentrations in patients with essential hypertension

Various doses (5 mg, 12.5 mg and 25 mg) of angiotensin I converting enzyme inhibitor (SQ 14,255, captopril) were administered to 8 patients with essential hypertension on a three-crossover study design, and the time course of mean blood pressure (MBP), plasma renin activity (PRA), plasma angiotensin converting enzyme activity (ACE-A), plasma cortisol (PC) and plasma aldosterone (PA) were determined following administration of the drug. MBP fell in a dose dependent manner, and PRA showed a minor but significant increases in cases receiving 5 and 12.5 mg of the drug. A large and significant increase in PRA was observed following 25 mg of captopril. ACE-A was also reduced in a dose dependent manner. There was no difference between changes in PC at any of the three dose levels. The serum potassium concentration was determined before and 3 hr after 25 mg of captopril treatment and no significant change was observed. In spite of the dose dependent and theoretical changes in the above parameters, lowered responses of PA to each dose of the drug were shown in reverse order against an increasing dose. That is to say, the grade of fall in PA following 25 of captopril was smaller than that following the other doses of the drug, and 5 mg induced a greater decrease in PA than 12.5 mg. Based on these findings, the relatively high dose of captopril in the present study was apparently more effective in increasing some factors which suppressed reduction of PA by a fall in angiotensin II than a low dose of the drug.     

Hormone and haemodynamic effects of angiotensin II infusion during captopril treatment for heart failure

Withdrawal of captopril therapy for cardiac failure results in increments in plasma cortisol, noradrenaline and heart rate. To determine whether these changes related to the concomitant rise in circulating angiotensin II, we infused angiotensin II at 0.5, 2, 4 and 8 ng/kg/minute, each infusion lasting for 1 hour, in 4 patients during maintenance captopril therapy for heart failure. A control solution of 5% dextrose was infused over a similar time interval on a separate day. The study was performed under metabolic balance conditions, with constant body posture and continuous haemodynamic monitoring. Angiotensin II induced the expected rise in arterial pressure and in plasma aldosterone. In contrast the diurnal decline in plasma ACTH and cortisol was not altered, and no changes in noradrenaline or heart rate were observed. Plasma angiotensin II appears to have little or no effect on ACTH, cortisol, noradrenaline and heart rate under the conditions of this study.     

Changes in the activity of the brain renin-angiotensin system and in the functional state of the pituitary-adrenal system of rats under the influence of captopril]

While studying the effect of peroral captopril injections on the activity of renin-angiotensin system (RAS), the activity of angiotensin-converting enzyme (ACE) and angiotensin II content from anterior and mediobasal hypothalamus, medulla and adenohypophysis of intact rats has been established to decrease. Captopril administration decreases ACE activity which increases after hydrocortisone injection in rat medulla and striatum. Captopril results in no potentiation of hormonal effect in hypothalamus and in adenohypophysis where ACE activity decreases following hydrocortisone injection. A decrease in the RAS activity of brain structures and adenohypophysis induced by captopril administration to rats is accompanied by the inhibition of the activity in the pituitary-adrenal system. A decrease in ACTH level and in 11-hydroxycorticosteroids of the rat blood plasma has been determined after single captopril injection in the dosage of 10 and 50 mg/kg of body weight. Duration of the effect depends on the captopril dosage.     

Angiotensin II and VEGF are involved in angiogenesis induced by short-term exercise training

Results from our laboratory have suggested a pathway involving angiotensin II type 1 (AT(1)) receptors and vascular endothelial growth factor (VEGF) in angiogenesis induced by electrical stimulation. The present study investigated if similar mechanisms underlie the angiogenesis induced by short-term exercise training. Seven days before training and throughout the training period, male Sprague-Dawley rats received either captopril or losartan in their drinking water. Rats underwent a 3-day treadmill training protocol. The tibialis anterior and gastrocnemius muscles were harvested under anesthesia and lightly fixed in formalin (vessel density) or frozen in liquid nitrogen (VEGF expression). In controls, treadmill training resulted in a significant increase in vessel density in all muscles studied. However, the angiogenesis induced by exercise was completely blocked by either losartan or captopril. Western blot analysis showed that VEGF expression was increased in the exercised control group, and both losartan and captopril blocked this increase. The role of VEGF was directly confirmed using a VEGF-neutralizing antibody. These results confirm the role of angiotensin II and VEGF in angiogenesis induced by exercise.