F. H. M. Derkx

Demonstration of renin mRNA, angiotensinogen mRNA, and angiotensin converting enzyme mRNA expression in the human eye: evidence for an intraocular renin-angiotensin system.

AIMS/BACKGROUND: All components necessary for the formation of angiotensin II, the biologically active product of the renin-angiotensin system (RAS), have been demonstrated in ocular tissue or vitreous and subretinal fluid. The tissue concentrations of renin were too high to be explained by admixture of blood. This raises the possibility of an intraocular RAS, independent of the RAS in the circulation. METHODS: In the present study, gene expression of RAS components in different parts of enucleated human eyes was investigated as evidence for tissue specific production. RESULTS: By using pooled tissue samples renin mRNA could be detected with the RNAse protection assay in retinal pigment epithelium (RPE) choroid, but not in neural retina or sclera. With reverse transcription polymerase chain reaction (RT-PCR), renin mRNA was detected in individual samples of RPE choroid and neural retina, and not anterior uveal tract or sclera. Angiotensinogen and angiotensin converting enzyme (ACE) gene expression could be demonstrated by RT-PCR in individual RPE choroid and neural retina samples and marginally in sclera samples. CONCLUSIONS: These results support the concept of intraocular synthesis of angiotensin II, independent of renin, angiotensin, and ACE in the circulation. Since gene expression was highest in ocular parts, which are highly vascularised, local angiotensin II may be involved in blood supply and/or pathological vascular processes such as neovascularisation in diabetic retinopathy.

The Place of Renal Scintigraphy in the Diagnosis of Renal Artery Stenosis: Fifteen Years of Clinical Experience

BACKGROUNDnRenal scintigraphy with radiolabeled pentetic acid (diethylenetriamine pentaacetic acid [DTPA]) or, more recently, mertiatide (mercaptoacetyltriglycine [MAG3]), with or without captopril challenge, is widely recommended as a diagnostic test for renal artery stenosis.nnnOBJECTIVESnTo address (1) whether the diagnostic accuracy has been improved by the use of captopril and the introduction of mertiatide and (2) whether a renal scan that shows abnormalities is a useful criterion to select patients for renal arteriography.nnnPATIENTS AND METHODSnA standard diagnostic protocol, using both scintigraphy and arteriography, was followed in 505 consecutive high-risk hypertensive patients who were evaluated for renovascular hypertension at the University Hospital Dijkzigt, Rotterdam, the Netherlands, from 1978 to 1992.nnnRESULTSnRenal artery stenosis (> or = 50%) was present in 263 patients. When the single-kidney fractional uptake was used as a diagnostic criterion, a specificity of 0.90 was obtained at a cutoff value of 35% for the worst kidney in scintigraphy using pentetic acid without captopril challenge (n = 225) and at a cutoff value of 37% after captopril challenge (n = 280). This was associated with sensitivity levels of 0.65 and 0.68, respectively. The difference between the uptake of pentetic acid with and without captopril challenge in the 85 patients who were studied under both circumstances was no more accurate as a predictor of renal artery stenosis. In the 93 patients who were studied with mertiatide as well as with pentetic acid, both after captopril challenge, the diagnostic accuracy was no better with mertiatide than with pentetic acid; mertiatide failed to offer any advantage not only when the single-kidney fractional uptake was used as a criterion, but also with the use of other scintigraphic parameters (eg, time to peak, time to pyelum, overall shape of renographic curve, and kidney size).nnnCONCLUSIONSnThe diagnostic accuracy of renal scintigraphy has not been improved by the introduction of mertiatide or by the use of captopril. The usefulness of scintigraphy as a diagnostic test for the presence of renal artery stenosis remains questionable. The physician will always confront either a substantial number of arteriograms that do not show abnormalities when renal scintigraphy is omitted as a screening step or a substantial number of missed diagnoses when a renal scan that shows abnormalities is used as a prerequisite for arteriography.

Prolonged blood pressure reduction by orally active renin inhibitor RO 42-5892 in essential hypertension.

OBJECTIVE--To investigate the effects of a novel specific renin inhibitor, RO 42-5892, with high affinity for human renin (Ki = 0.5 x 10(-9) mol/l), on plasma renin activity and angiotensin II concentration and on 24 hour ambulatory blood pressure in essential hypertension. DESIGN--Exploratory study in which active treatment was preceded by placebo. SETTING--Inpatient unit of teaching hospital. PATIENTS--Nine men with uncomplicated essential hypertension who had a normal sodium intake. INTERVENTIONS--Two single intravenous doses of RO 42-5892 (100 and 1,000 micrograms/kg in 10 minutes) given to six patients and one single oral dose (600 mg) given to the three others as well as to three of the patients who also received the two intravenous doses. RESULTS--With both intravenous and oral doses renin activity fell in 10 minutes to undetectably low values, while angiotensin II concentration fell overall by 80-90% with intravenous dosing and by 30-40% after the oral dose. Angiotensin II concentration was back to baseline four hours after the low and six hours after the high intravenous dose and remained low for at least eight hours after the oral dose. Blood pressure fell rapidly both after low and high intravenous doses and after the oral dose and remained low for hours. With the high intravenous dose the daytime (0900-2230), night time (2300-0600), and next morning (0630-0830) systolic blood pressures were significantly (p less than 0.05) lowered by 12.5 (95% confidence interval 5.6 to 19.7), 12.2 (5.4 to 19.3), and 10.7 (3.2 to 18.5) mm Hg respectively, and daytime diastolic pressure was lowered by 9.3 (2.2 to 16.8) mmHg. With the oral dose daytime, night time, and next morning systolic blood pressures were lowered by 10.3 (5.5 to 15.4), 10.5 (4.2 to 17.2), and 9.7 (4.0 to 15.6) mm Hg, and daytime and night time diastolic pressures were lowered by 5.8 (0.9 to 11.0) and 6.0 (0.3-12) mm Hg respectively. CONCLUSIONS--The effect of the inhibitor on blood pressure was maintained over a longer period than its effect on angiotensin II. RO 42-5892 is orally active and has a prolonged antihypertensive effect in patients who did not have sodium depletion. This prolonged effect seems to be independent, at least in part, of the suppression of circulating angiotensin II.

Human renal and systemic hemodynamic, natriuretic, and neurohumoral responses to different doses of L-NAME

Experimental evidence indicates that the renal circulation is more sensitive to the effects of nitric oxide (NO) synthesis inhibition than other vascular beds. To explore whether in men the NO-mediated vasodilator tone is greater in the renal than in the systemic circulation, the effects of three different intravenous infusions of NG-nitro-L-arginine methyl ester (L-NAME; 1, 5, and 25 microg. kg-1. min-1 for 30 min) or placebo on mean arterial pressure (MAP), systemic vascular resistance (SVR), renal blood flow (RBF), renal vascular resistance (RVR), glomerular filtration rate (GFR), and fractional sodium and lithium excretion (FENa and FELi) were studied in 12 healthy subjects, each receiving randomly two of the four treatments on two different occasions. MAP was measured continuously by means of the Finapres device, and stroke volume was calculated by a model flow method. GFR and RBF were estimated from the clearances of radiolabeled thalamate and hippuran. Systemic and renal hemodynamics were followed for 2 h after start of infusions. During placebo, renal and systemic hemodynamics and FENa and FELi remained stable. With the low and intermediate L-NAME doses, maximal increments in SVR and RVR were similar: 20.4 +/- 19.6 and 23.5 +/- 16.0%, respectively, with the low dose and 31.4 +/- 26.7 and 31.2 +/- 14.4%, respectively, with the intermediate dose (means +/- SD). With the high L-NAME dose, the increment in RVR was greater than the increment in SVR. Despite a decrease in RBF, FENa and FELi did not change with the low L-NAME dose, but they decreased by 31.2 +/- 11.0 and 20.2 +/- 6.3%, respectively, with the intermediate dose and by 70.8 +/- 8.1 and 31.5 +/- 15.9% with the high L-NAME dose, respectively. It is concluded that in men the renal circulation is not more sensitive to the effects of NO synthesis inhibition than the systemic circulation and that the threshold for NO synthesis inhibition to produce antinatriuresis is higher than the threshold level to cause renal vasoconstriction.Experimental evidence indicates that the renal circulation is more sensitive to the effects of nitric oxide (NO) synthesis inhibition than other vascular beds. To explore whether in men the NO-mediated vasodilator tone is greater in the renal than in the systemic circulation, the effects of three different intravenous infusions of N G-nitro-l-arginine methyl ester (l-NAME; 1, 5, and 25 μg ⋅ kg-1 ⋅ min-1for 30 min) or placebo on mean arterial pressure (MAP), systemic vascular resistance (SVR), renal blood flow (RBF), renal vascular resistance (RVR), glomerular filtration rate (GFR), and fractional sodium and lithium excretion (FENaand FELi) were studied in 12 healthy subjects, each receiving randomly two of the four treatments on two different occasions. MAP was measured continuously by means of the Finapres device, and stroke volume was calculated by a model flow method. GFR and RBF were estimated from the clearances of radiolabeled thalamate and hippuran. Systemic and renal hemodynamics were followed for 2 h after start of infusions. During placebo, renal and systemic hemodynamics and FENa and FELi remained stable. With the low and intermediate l-NAME doses, maximal increments in SVR and RVR were similar: 20.4 ± 19.6 and 23.5 ± 16.0%, respectively, with the low dose and 31.4 ± 26.7 and 31.2 ± 14.4%, respectively, with the intermediate dose (means ± SD). With the high l-NAME dose, the increment in RVR was greater than the increment in SVR. Despite a decrease in RBF, FENaand FELi did not change with the low l-NAME dose, but they decreased by 31.2 ± 11.0 and 20.2 ± 6.3%, respectively, with the intermediate dose and by 70.8 ± 8.1 and 31.5 ± 15.9% with the highl-NAME dose, respectively. It is concluded that in men the renal circulation is not more sensitive to the effects of NO synthesis inhibition than the systemic circulation and that the threshold for NO synthesis inhibition to produce antinatriuresis is higher than the threshold level to cause renal vasoconstriction.

Resistance to antihypertensive medication as predictor of renal artery stenosis: comparison of two drug regimens.

Background: Renal artery stenosis is among the most common curable causes of hypertension. The definitive diagnosis is made by renal angiography, an invasive and costly procedure. The prevalence of renal artery stenosis is less than 1% in non-selected hypertensive patients but is higher when hypertension is resistant to drugs.Objective: To study the usefulness of standardised two-drug regimens for identifying drug-resistant hypertension as a predictor of renal artery stenosis.Design and setting: Prospective cohort study carried out in 26 hospitals in The Netherlands.Patients: Patients had been referred for analysis of possible secondary hypertension or because hypertension was difficult to treat. Patients ⩽40 years of age were assigned to either amlodipine 10u2009mg or enalapril 20u2009mg, and patients >40 years to either amlodipine 10u2009mg combined with atenolol 50u2009mg or to enalapril 20u2009mg combined with hydrochlorothiazide 25u2009mg. Renal angiography was performed: (1) if hypertension was drug-resistant, ie if diastolic pressure remained ⩾95 mmu2009Hg at three visits 1–3 weeks apart or an extra drug was required, and/or (2) if serum creatinine rose by ⩾20u2009μmol/L (⩾0.23u2009mg/dL) during ACE inhibitor treatment.Results: Of the 1106 patients with complete follow-up, 1022 had been assigned to either the amlodipine- or enalapril-based regimens, 772 by randomisation. Drug-resistant hypertension, as defined above, was identified in 41% of the patients, and 20% of these had renal artery stenosis. Renal function impairment was observed in 8% of the patients on ACE inhibitor, and this was associated with a 46% prevalence of renal artery stenosis. In the randomised patients, the prevalence of renal artery stenosis did not differ between the amlodipine- and enalapril-based regimens.Conclusions: In the diagnostic work-up for renovascular hypertension the use of standardised medication regimens of maximally two drugs, to identify patients with drug-resistant hypertension, is a rational first step to increase the a priori chance of renal artery stenosis. Amlodipine- or enalapril-based regimens are equally effective for this purpose.

Predictors for clinical success at one year following renal artery stent placement.

Purpose: To determine pretreatment variables that may predict 1-year clinical outcome of stent placement for renal artery stenosis. Methods: In a prospective study, 40 consecutive patients (29 men; mean age 60 ± 9.1 years) with angiographically proven atherosclerotic renal artery stenosis were treated with stent placement because of drug resistant hypertension (n=14), renal function impairment (n=14), or both (n=12). Clinical success at 1 year was defined as a decrease of diastolic blood pressure ≥10 mmHg or a decrease in serum creatinine ≥20%, depending on the indication for treatment. Regression analysis was performed using anatomical parameters from angiography and intravascular ultrasound, estimates of renal blood flow from renal scintigraphy, and single-kidney renal function measurements. Results: Patients treated for hypertension had better outcome than those treated for renal function impairment, with clinical success rates of 85% and 35%, respectively. Preserved renal function, with low serum creatinine and high 2-kidney glomerular filtration rate at baseline, was associated with clinical success in the entire patient group at follow-up (p=0.02 and p=0.03, respectively). An elevated vein-to-artery renin ratio on the affected side was borderline predictive (p=0.06). In patients treated for renal impairment, lateralization to the affected kidney (affected kidney—to–2-kidney count ratio ≤0.45) on the scintigram emerged as a significant predictor for clinical success, with an odds ratio of 15 (p=0.048). Conclusions: Clinical success of renal artery stent placement is better for the treatment of hypertension than for preserving renal function. In patients with renal function impairment, lateralization to the affected kidney on the scintigram appears to be a predictor of clinical success.

Renin inhibitors, angiotensin converting enzyme inhibitors and angiotensin II receptor antagonists : relationships between blood pressure responses and effects on the renin-angiotensin system

AIMnTo compare the effects of angiotensin converting enzyme (ACE) inhibitors, renin inhibitors and angiotensin II (Ang II) antagonists.nnnMETHODnSurvey of data from recent studies. DISCREPANCY BETWEEN BLOOD PRESSURE REDUCTION INDUCED BY ACE INHIBITORS AND PLASMA ANG II LEVELS: Studies on the effects of ACE inhibition in hypertensive subjects have suggested that with chronic ACE inhibitor treatment, blood pressure remains lowered even when plasma Ang II returns to normal. However, this discrepancy may be largely an artefact related to difficulties in measuring low Ang II levels in the presence of high angiotensin I (Ang I) levels. Even with modern sensitive and specific Ang II assays it can be difficult to monitor in vivo ACE inhibition (Ang II:I ratio in plasma) because of ex vivo Ang II formation. Recently, in measuring 24-h blood pressure responses to ACE inhibitor treatment, we have obtained good correlations between the time-course of the blood pressure response and the change in circulating Ang II. PROBLEMS IN MEASURING RENIN ACTIVITY: Routine assays of renin activity in plasma can lead to an overestimate of the degree of in vivo inhibition during renin inhibitor treatment, because some protease inhibitors that are used in these assays can cause an ex vivo displacement of protein-bound renin inhibitor, thereby increasing its free concentration. This must be taken into account when using the ratio of enzymatically active renin to immunoreactive renin as an index of in vivo renin inhibition. BLOOD PRESSURE RESPONSE AND ANG II LEVELS WITH RENIN INHIBITORS AND ANG II ANTAGONISTS: Results published so far seem to indicate that with these drugs, as with the ACE inhibitors, the magnitude of the blood pressure effect is correlated with the decrease in the effective Ang II concentration at the receptor sites. However, the time-course of the two effects may be different; with the renin inhibitors, the maximum effect on pressure was delayed compared with the effect on Ang II.nnnCONCLUSIONSnFurther studies are needed to establish the exact time-course of renin and Ang II changes and their relationship to blood pressure. Only with rigorously controlled assays will it be possible to answer the question whether, for a given change in effective Ang II concentration at the receptor sites, the effect on blood pressure is different with the three classes of anti-renin-angiotensin drugs.

Captopril in the Treatment of Hypertension with Renal Artery Stenosis

Although the role of the renin angiotensin system in the initiation of renovascular hypertension is well established, it has proved difficult to demonstrate that renin or angiotensin levels are high enough to be responsible for the maintenance of this form of hypertension (1). Recently pharmacological dissection of the different components of the renin angiotensin system has become a clinical reality. Claims have been made that administration of drugs which block either angiotensin II’s action (saralasin) or its formation (angiotensin converting enzyme inhibitors, teprotide and captopril) can be used to identify the participation of the renin angiotensin system in elevated blood pressure and to select surgically curable forms of hypertension (2). In this regard especially captopril is interesting because it is orally active and both short-term and long-term responses can be studied. However, despite much speculation in the literature, the mechanism of captopril’s blood pressure lowering effect has not been fully clarified (3). It is attractive to opt for simplicity and to accept that the drug exerts its effect solely through prevention of angiotensin II formation. Indeed the fall in blood pressure shortly after a single dose of captopril correlated positively with pretreatment plasma renin levels in some studies. However this is not invariably so, and this becomes even more evident during long-term treatment (4). There exists a potential problem of specificity. Angiotensin converting enzyme is identical with kininase II and by this way it is involved in the inactivation of bradykinin. Accumulation of the vasodilator bradykinin can contribute directly to the blood pressure lowering effect of captopril but also indirectly because this hormone is involved in the release of prostaglandins as well. Theoretically, it is also possible that the change in vascular resistance after captopril rather than the effect on blood pressure is correlated with pretreatment renin.

Plasma Kallikrein as an Activator of Inactive Renin (“Prorenin”) — Studies In-Vitro and In-Vivo

Most proteolytic enzymes in plasma circulate as inactive precursors. These proenzymes are activated by limited proteolysis during physiological processes such as coagulation, fibrinolysis and complement-mediated reactions [1, 2], For a long time most physiologists and clinicians were interested in renin as a classical circulating hormone [3], despite the well-known fact that renin is a proteolytic enzyme [4, 5]. The traditional endocrinologist’s view, however, seems too limited. Recently it has become clear that renin circulates in plasma largely as an inactive form, which might be a proenzyme, prorenin, comparable to other proenzymes in plasma [6–10].