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D Stephan

Publications and source records attributed to D Stephan.

At least 55 records · Page 3Linked to original sources
PubMed1996

Human metabotropic glutamate receptor 1: mRNA distribution, chromosome localization and functional expression of two splice variants.

We have isolated clones from a human brain cDNA library coding for two splice variants of mGluR1. The combined sequences account for 6864 base pairs (bp) of the approximately 7 kilobase (kb) transcript seen on northern blots of human brain mRNA. The distribution of mGluR1 mRNA in human brain is similar to that found in rat brain and the gene for mGluR1 is localized on human chromosome 6. The mRNA for mGluR1 alpha contains an open reading frame that codes for a 1194 amino acid protein, which is slightly smaller than rat mGluR1 alpha. The major structural difference noted between the human and rat mGluR1 is a deletion of 21 nucleotides which would result in the loss of seven amino acids in the middle of a proline- and glutamine-rich region of the C-terminal tail of mGluR1 alpha. The 85 bp exon that results in the HmGluR1 beta splice variant was found to code for a protein with two amino acid differences compared to the rat receptor. Functional and pharmacological characterization of heterologously expressed human mGluR1 was performed using electrophysiological recordings from Xenopus oocytes and calcium imaging in HEK-293 cells. No major differences were found in the response of human mGluR1 to typical agonists and antagonists compared to the rat, or in the behavior of the two splice variants.

Alternative Splicing↗
PubMed1996

Interruption of prolonged ramipril treatment in hypertensive patients: effects on the renin-angiotensin system.

The increase in renin secretion and the induction of the converting enzyme (ACE) observed during treatment by ACE inhibitors (CEIs) could result in increased angiotensin II (ang II) synthesis when the treatment is stopped. The object of this study was to compare changes in the components of the renin-angiotensin system with changes in arterial pressure in hypertensives, following the cessation of long-term ramipril treatment. Twenty hypertensives, treated for at least three months with ramipril, in monotherapy for the last three weeks, were randomly allocated to two parallel groups and received for fifteen days, on a double-bind basis, either a placebo (withdrawal group W, n = 12) or ramipril at the previous doses (treated group T, n = 8). Blood pressure was measured using four different techniques. The active renin (AR), angiotensinogen, angiotensin I (ang I), angiotensin II (ang II) and aldosterone plasma concentrations were measured, as was plasma angiotensin I converting enzyme (ACE) activity in vitro (colorimetric and fluorimetric method) and in vivo (the ang II/ang I ratio). The biological effects of cessation of long-term ramipril treatment in hypertensives were a decline in AR and angiotensin I concentrations, an increase in ACE activity and no significant changes in angiotensinogen, angiotensin II and aldosterone levels. Fifteen days after withdrawal, the different parameters of the renin-angiotensin system appear to have returned to basal value. A slow rise in blood pressure was also observed but no rebound increase was noted during the 15 days neither in angiotensin II levels nor in blood pressure. Following the cessation of prolonged ramipril treatment, in vivo converting enzyme inhibition disappears slowly, probably on account of the slow tight binding inhibitor properties of ramiprilat, the active metabolite of this CEI. The gradual decline in AF, plasma levels, together with the prolonged ACE inhibition as measured in vivo by the ang II/ang I ratio, explains the absence of a rise in ang II synthesis.

Aldosterone↗
PubMed1996

Gene transfer approaches to the regulation of vascular cell proliferation.

Considerable progress has been made in identifying potential targets for treating vascular proliferative diseases. In this review, we discuss gene transfer approaches to regulating smooth muscle cell proliferation after vascular injury using the cell cycle specific proteins, p21, delta Rb and HSV-tk. Results from these studies suggest that replicating smooth muscle cells and macrophages are inhibited in vivo in several animal models of restenosis, including hyperlipidaemic vessels. Identification of appropriate vascular diseases and improvements in gene delivery and vectors will require careful optimization in order to develop effective molecular therapies for human vascular diseases.

Animals↗
PubMed1995

Stereoselective renal effects of the loop diuretic ozolinone in the anesthetized dog.

The renal effects of i.v. injections of (+/-)-ozolinone, its enantiomers (-)-ozolinone and (+)-ozolinone and its prodrug (+/-)-etozoline, were compared with those of furosemide, in pentobarbital anesthetized dogs. Renal blood flow (electromagnetic flow-meter) and glomerular filtration rate (polyfructosan clearance) were assessed on the left denervated kidney together with renin secretion and urinary electrolyte excretion. (-)-Ozolinone (15.5 mg/kg i.v.) behaves as a stereoselective loop diuretic equipotent to 20 mg/kg of furosemide and 45 mg/kg of (+/-)-ozolinone; (+)-ozolinone induced only minor salidiuretic effects. Both ozolinone enantiomers markedly increased the renal blood flow and decreased the filtration fraction, suggesting that the vosodilating effect predominates on the efferent glomerular arterioles. (-)-Ozolinone also induced an acute rise in renin secretion. The inhibition of prostaglandin synthesis (indomethacin or meclofenamate) prevented renin hypersecretion in response to (-)-ozolinone and modified its salidiuretic effects but had no effect on the vascular response. The inhibition of the kallikrein-kinin system by aprotinin had no effect on the overall renal response to (-)-ozolinone. The inhibition of the renin-angiotensin system by captopril decreased blood pressure, prolonged the (-)-ozolinone-induced decrease in renal vascular resistance and increased renin secretion. Our results demonstrate that the loop diuretic, ozolinone, induces stereoselective and prostaglandin-dependent renin secretion, which is involved in the regulation of intra-renal hemodynamics.

Analysis of Variance↗
PubMed1995

Endothelium-dependent relaxation in the isolated rat kidney: impairment by cyclosporine A.

The therapeutical use of cyclosporine A (CsA) is hampered by the development of nephrotoxicity characterized by a marked increase in renal vascular resistance (RVR). We investigated vascular functions in kidneys of rats treated with CsA. The ex vivo vascular reactivity of kidneys from control rats and animals treated subacutely with CsA [50 mg/kg/day subcutaneously (s.c.) for 16-21 days] or an olive oil vehicle (1 ml/kg) was analyzed in male Wistar rats. The right kidney was isolated and perfused with Tyrode's or Krebs solution in an open circuit. The effects of acetylcholine (Ach), fenoldopam (FEN), and sodium nitroprusside (SNP) on norepinephrine (NE) preconstricted kidneys were studied. In control kidneys (untreated or vehicle-treated), Ach induced a relaxation (EC50 = 0.56 +/- 0.05 x 10(-9)M; Emax = 88.2 +/- 2.1% decrease in the vascular tone restored by NE) which was endothelium-dependent [near-complete abolition after treatment with a detergent, 3-[(3-cholamidopropyl)-dimethyl-ammonio]-1-propane-sulfonate (CHAPS) treatment] but only partially inhibited by indomethacin (EC50 = 1.71 +/- 0.39 x 10(-9)M, p < 0.05; Emax = 87.1 +/- 4.9%, NS) or indomethacin with NG-nitro-L-arginine methyl ester (L-NAME: EC50 = 1.04 +/- 0.38 x 10(-9)M, NS; Emax = 63.8 +/- 2.5%, p < 0.01). CsA treatment induced a marked decrease in creatinine clearance and natriuresis measured in vivo but had no effect on systolic blood pressure (SBP). In CsA-treated rats, Ach-induced renal relaxation was partially blunted (EC50 = 1.88 +/- 0.34 x 10(-9)M, p < 0.01; Emax = 82.8 +/- 4.6, NS), with both a defect in prostaglandin (PG) and nitric oxide (NO)-related responses. CsA treatment had no effect on endothelium-independent relaxations induced by FEN and SNP. These results show that subacute CsA treatment selectively impairs renal endothelium-dependent relaxation related to PGs and NO release.

Animals↗
PubMed1995

[Ramipril and cardiac and renal angiotensin converting enzyme].

The role of the angiotensin converting enzyme (ACE) in the regulation of local synthesis of angiotensin II has not been clearly defined. The authors investigated the local factors which might orientate the effects of ACE inhibitors to particular organs in the Wistar rat. The in vivo study of the effects of low doses of ramipril on the myocardium showed that cardiac ACE was significantly inhibited by the non-antihypertensive dose of 0.01 mg/kg whereas the inhibition only occurred from doses higher than 0.1 mg/kg in the other tissues studied. In the kidney: the affinity of 3H-ramiprilate for the brush borders of the proximal tubular cells was increased by high concentrations of chloride ions as observed in the renal parenchyma, the presence of esterases makes local activation of ramipril (diester) into ramiprilate (active diacid) possible, prolonged treatment with ramipril leads to a lowering of the concentration of ACE in the brush border of the proximal tubular cells, verified after the elimination of the ACE inhibitor fixed on the tissue. These data indicate that the myocardium and the kidney could be privileged targets of the action of ramipril.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1995

[Relation between plasma renin level and antihypertensive response to nicardipine].

The antihypertensive efficacy of calcium antagonists could depend on the concentration of circulating renin. To investigate this hypothesis, 102 hypertensive men or women were included in this study. After an initial 2 week placebo period, the patients were administered slow-release nicardipine, 50 mg twice a day for twelve weeks. The blood pressures were measured with a mercury sphygmomanometer at inclusion (S2) and after 12 weeks of treatment (S14), in addition to home automeasure during the week before inclusion and the two weeks preceding the final visit. The plasma renin activity (RA) was measured at S2 and S14. Its value at inclusion was used to differentiate patients with low renin (< or = 11 ng/l) from those with normal (> 11 < or = 17 ng/l) or high renin activity (> 17 ng/l). The blood pressure measured by sphygmomanometer or automeasure was significantly lower at the end of the active treatment period (SBP: -8 mmHg; DBP: -9.5 mmHg; and SBP: -5.8 mmHg; DBP: -5.7 mmHg respectively); the reduction in blood pressure was significantly higher in the group with low RA than in the group with high RA. The reductions in SBP measured in the morning and evening and in DBP measured in the morning were significantly greater in the group with low RA than in the group with high RA. The reduction of SBP measured in the morning at midday, and in the evening was correlated to the basal value of RA. Mild side effects were observed in 20 patients leading to the interruption of treatment in 11 cases because of headache. The best antihypertensive response is observed in patients with low plasma RA. This could explain the good response to calcium antagonists usually observed in elderly hypertensives.

Blood Pressure↗
PubMed1994

Vascular effects of loop diuretics: an in vivo and in vitro study in the rat.

The vascular effects of loop diuretics were studied in two models designed to eliminate hemodynamic repercussions linked to sodium and water depletion: in vivo, in unilaterally nephrectomized rats with a contralateral uretero-venous shunt, and in vitro, in the isolated perfused rat kidney. In anesthetized rats, local vascular resistance was calculated from the simultaneous recording of blood pressure and renal, iliac and carotid blood flows (electromagnetic flowmeter, Skalar). Furosemide and piretanide (10 to 80 mg/kg i.v.) induced a comparable dose-dependent decrease in renal vascular resistance, which was not modified by reserpine and indomethacin pre-treatment. The iliac relaxing response was blunted by vasoconstriction, which disappeared after combined treatment with reserpine and indomethacin. The relaxation induced in the iliac and carotid vasculature persisted after bilateral nephrectomy. In vitro, the vasorelaxing effect of diuretics in isolated rat kidneys perfused in an open circuit was studied after vascular tone had been re-established by a continuous perfusion of PGF2 alpha. Furosemide, piretanide and ozolinone induced a concentration-dependent decrease in renal tone (EC50 = 0.47 x 10(-4) mol/l, 1.03 x 10(-4) mol/l and 2.07 x 10(-4) mol/l respectively) in Wistar rats. A similar response to piretanide was found in spontaneously hypertensive stroke-prone rats (EC50 = 0.32 x 10(-4) mol/l) and in their normotensive controls (EC50 = 0.74 x 10(-4) mol/l). Our results show that loop diuretics induce a direct relaxation in the renal, iliac and carotid vasculature. This vascular effect, which appears at relatively high concentrations of the drugs, is prostaglandin independent and persists after bilateral nephrectomy.

Animals↗
PubMed1994

Short-term effects of quinapril and nifedipine on early renal changes in streptozotocin-induced diabetes in rats.

The effects on renal function of quinapril, an angiotensin I converting enzyme (ACE) inhibitor, and of nifedipine, a dihydropyridine calcium antagonist, were studied in the early stages of diabetes in rats. Wistar rats received one injection of streptozotocin (STZ) to induce diabetes; the hyperglycaemia was then controlled with daily insulin therapy (2-3 units NPH insulin/rat). One week after STZ injection, rats were treated orally with quinapril (0.3 or 3 mg/kg/d) or nifedipine (30 mg/kg/day) for 1 week, after which renal functions were compared with those of untreated diabetic rats or non-diabetic control rats. At the end of these two weeks, diabetic rats had gained less weight and had developed renal hypertrophy and glomerular hyperfiltration (3.21 +/- 0.23 vs 2.36 +/- 0.09 ml/min for non-diabetic rats, mean +/- SEM, P < 0.01). Their urinary albumin excretion was higher, as was the urinary excretion of water, sodium, potassium, urea and glucose. One week treatment with quinapril or nifedipine had no significant effect on the increase in the glomerular filtration rate (respectively 2.97 +/- 0.18 and 2.99 +2- 0.15 ml/min). Quinapril and nifedipine differed with regard to their effects on urinary albumin excretion. Albuminuria was increased by nifedipine but not by quinapril (respectively 0.554 +/- 0.158 and 0.149 +/- 0.046 mg/day/100 g BW, P < 0.05). This difference between the effects of the dihydropyridine and the ACE inhibitor on albuminuria may be linked to different effects on the glomerular functions.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1994

Plasma renin activity and changes in tissue angiotensin converting enzyme.

OBJECTIVES: Recent evidence suggests that tissue generation of angiotensins I and II depends on the level of the plasma components of the renin-angiotensin system and on tissue-specific processes. The present study was undertaken to clarify the possible relationship between plasma renin activity (PRA) and tissue angiotensin converting enzyme (ACE) activity in the heart, lung, kidney cortex and kidney medulla of Wistar-Kyoto rats. In the kidney cortex particular attention was focused on renal brush-border ACE. METHODS: Different experimental models known to have opposite effects on PRA were used: changes in salt intake, deoxycorticosterone acetate (DOCA) with or without salt supplements, and the Goldblatt two-kidney, one clip (2-K,1C) model. Two weeks after the start of the experiments the rats were killed, and PRA, and plasma and tissue ACE activity, were measured. RESULTS: At the end of the study the blood pressure in the treated rats was not significantly different from control. As expected, the PRA were highest in the 2-K,1C and depleted-salt groups and lowest in the DOCA, DOCA-salt and high-salt groups. ACE responses were different in different types of tissue, with no relationship between PRA and plasma or tissue ACE activity. For example, DOCA treatment led to increased ACE activity in the heart and the kidney only if the rats were maintained on a high salt intake. DOCA or salt alone failed to have this effect. In the 2-K,1C model the unclipped kidneys did not show any significant variation in ACE activity, but the clipped kidneys exhibited increased ACE activity compared with sham-operated rats. This increase, coupled with increased renal renin secretion, could play a role in the acceleration of local angiotensin II formation, and could thus initiate and sustain the development of hypertension in this model. CONCLUSION: The present results show that variations in ACE activity were organ-specific and were not linked either to hypertension or to changes in PRA.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1993

Effects of one-hour and one-week treatment with ramipril on plasma and renal brush border angiotensin converting enzyme in the rat.

Prolonged treatment with an angiotensin converting enzyme inhibitor produces an induction of plasma angiotensin converting enzyme. Induction of angiotensin converting enzyme in tissues during prolonged treatment with an angiotensin converting enzyme inhibitor is less well documented. We compared the effects of 1 h and 1 week treatment with ramipril (0.1, 0.3, 1 mg/kg) on angiotensin converting enzyme activity in the plasma, renal cortex and renal brush border membrane of Wistar rats. As an increase in activity could be masked by the inhibition due to the presence of ramiprilat which is the active form of ramipril, we eliminated the ramiprilat present in renal cortex homogenates with EGTA during brush border preparation. The 1-h treatment with ramipril induced a dose-dependent inhibition of plasma and renal cortex angiotensin converting enzyme activity. The 1-week treatment with ramipril produced an increase in plasma angiotensin converting enzyme activity, whereas renal cortex angiotensin converting enzyme activity decreased. The decrease in angiotensin converting enzyme activity persisted in the brush border membrane after elimination of residual ramiprilat with EGTA. Our results show that prolonged ramipril treatment produces opposite responses in plasma and renal cortex angiotensin converting enzyme activity, suggesting that plasma and epithelial angiotensin converting enzymes are subject to specific local regulatory factors.

Animals↗
PubMed1993

Renal dopamine excretion in healthy volunteers after oral ingestion of L-dopa.

L-Dopa is converted to dopamine by aromatic-L-amino acid decarboxylase (AADC). In the kidney, proximal tubular epithelial cells are rich in AADC and urinary free dopamine excretion is a marker for endorenal extraneuronal dopamine synthesis. The urinary free dopamine excretion was analysed in a double-blind cross-over study after oral ingestion of L-Dopa or a placebo in five healthy volunteers. The drug ingestions were separated by one week's wash-out. Since in a preliminary study, two volunteers ingesting a single L-Dopa dose of 500 mg with breakfast experienced nausea, the five volunteers of the present study were given 300 mg L-Dopa (50 mg at 9 am with breakfast, 100 mg before lunch and 150 mg before dinner) without any adverse effects. L-Dopa induced an increase in 24-h urinary dopamine excretion (HPLC with electrochemical detection). Free urinary dopamine (1900 micrograms/24 h) accounted for 0.8% of the daily oral L-Dopa dose and represented 10% of total urinary dopamine excretion. L-Dopa treatment had no significant effect on mean ambulatory arterial blood pressure and heart rate measured from 9 am to 6 pm (Spacelabs) or on 24 h urinary water and sodium excretion.

Adult↗
PubMed1993

[Changing of renal endothelium-dependent vascular reactivity by cyclosporin A].

Clinical use of the immunosuppressant cyclosporine A (CSA) is hampered by its nephrotoxicity. The renal vascular resistance is increased, may be as a consequence of a deleterious effect of the drug on the vascular endothelial cell function. The renal effects of a subchronic treatment with CSA (50 mg/kg/d, sc, 18 days), or olive oil vehicule (1 ml/kg), were studied in normotensive male Wistar rats. Creatinine clearance was measured on 24 h urine collection before the right kidney of the animals was isolated and perfused in an open circuit at 6 ml/min with Tyrode's solution. Renal vasodilator responses to acetylcholine (ACH, 10(-10) to 10(-7) M) and sodium nitroprusside (NP, 3 x 10(-9) to 3 x 10(-6) M) were studied after reestablishment of a renal vascular tone by a continuous perfusion of noradrenaline (NA, 10(-7) M). ACH was more potent than NP to induce renal vasodilation (EC50 = 0.57 +/- 0.05 x 10(-9) M, n = 8, vs 3.42 +/- 0.29 x 10(-8) M, n = 5), but both drugs reversed the NA-induced vasoconstriction by near 90%. L-NAME (3 x 10(-5) M) had no effect on NP-induced renal relaxation but suppressed responses to low concentrations of ACH and decreased by half its Emax (47 +/- 17%).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1993

[Captopril test for detecting renal artery stenosis: changes in plasma renin concentration].

The aim of this study was to demonstrate the diagnostic value of changes in active renin concentration during the captopril test (measurements of plasmatic active renin concentrations, before 12.5 or 37.5 mg of captopril p.o., and 30 and 90 minutes after) in order to screen a significant renal artery stenosis. After a renal angiography, 88 hypertensive patients suspected of renovascular hypertension were classified according to the percentage of stenosis in the main renal artery: class I (< 30% - n = 50), II (30 to < 75% - n = 21), III (75 to < 90% - n = 8) and IV (90 to 100% - n = 11). The results of the captopril test were compared to those of renal angiography. The active renin before the test (basal AR), the greater increase in active renin after captopril (max AR), the difference between max AR and basal AR (DIF) and the active renin relative change after the test (RC) were compared in the 4 classes (ANOVA). There were no differences in diastolic blood pressure (> or = 90 mmHg) natriuresis (100 mmol/24 h in mean) between these different classes. The basal AR, the max AR, the DIF and the RC significantly differed between the 4 classes. They were greater in class III and IV than in class I. The positive criteria for the captopril test were max AR, DIF and RC. The positivity thresholds were max AR > or = 70 ng/l, DIF > or = 50 ng/l and RC > or = 165% (upper limit in the class I 95% confidence interval for each criterion).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1993

[Ambulatory or single measurement of blood pressure: comparison in a controlled trial in patients with hypertension].

Single measurement during a visit and the calculation of blood pressure pattern from an ambulatory record are different criteria for evaluation of the efficacy of antihypertensive treatment. Results obtained by these two methods were compared in a controlled trial. Acebutolol or enalapril were given double-blind to 17 patients with uncomplicated moderate essential hypertension. After a two week run-in period (with dummy treatment), patients were allocated at random into two parallel groups. They took acebutolol (400 mg) or enalapril (20 mg) as a single daily dose for 3 months. Ambulatory measurement of blood pressure for 24 hours (Spacelabs 5200 SPM) was carried out the day prior to final inclusion, and at the end of the first then the third month of active treatment. A single measurement of blood pressure took place at the same times. Safety/acceptability of treatment based upon clinical and laboratory parameters was good. At inclusion, single measurements showed that all patients had a diastolic blood pressure (DBP) over 95 mmHg. However, ambulatory BP was significantly lower in the enalapril group. With treatment, the fall in DBP by single measurement was significant only at the first month with enalapril and at the third month with acebutolol while the effects of both drugs were significant on ambulatory systolic blood pressure (SBP) and DBP by the first month. Ambulatory BP revealed a superior antihypertensive action of acebutolol on SBP at the third month but this was not shown by single BP measurements. These results confirm the specificity of trial protocols of antihypertensive drugs based upon ambulatory BP measurements.

Acebutolol↗
PubMed1992

In vitro stability of the inhibition of serum converting enzyme by fosinopril.

With captopril, it has been shown that an erroneous measurement of serum angiotensin converting enzyme (ACE) can be induced by the dissociation of the inhibitor-ACE complex during long-term storage. We have studied the possible dissociation of the fosinopril-ACE complex during the storage of serum samples from healthy male volunteers given a single dose of fosinopril. Serum samples were collected from 5 volunteers, 5 min before, then 4 and 24 h after a unique oral dose of 10 mg fosinopril. ACE activity was measured by a colorimetric and a fluorimetric assay during the hour following the sampling (day 0) and after 21 or 61 days of storage at -20 or -196 degrees C. The degree of ACE inhibition measured in vitro in fresh serum samples differed according to the technique used. Fosinopril has a long-lasting effect with 80% inhibition 24 hours after drug administration. Storage at -20 and -196 degrees C induced a significant decrease in the degree of inhibition measured with the colorimetric method. With the fluorimetric method, a decrease in ACE inhibition was only observed after storage at -20 degrees C but not at -196 degrees C.

Administration, Oral↗
PubMed1991

The effects of muzolimine and urine from muzolimine-treated rats on Na+K+Cl- cotransport in Madin-Darby canine kidney cells.

Muzolimine is a loop diuretic with an original chemical structure devoid of the acidic or sulfonamide group known to be necessary for an interaction with Na+K+Cl- cotransport. We studied the effects of urine from muzolimine-treated rats on the Na+K+Cl- cotransport-dependent 86Rb influx in MDCK cells. Na+K+Cl- cotransport was inhibited by urine obtained 15 min (42% inhibition) and 60 min (49% inhibition) after muzolimine injection (50 mumol/kg i.v.). Muzolimine itself was not detectable in the urine. Probenecid (100 mumol/kg i.v.) suppressed both the diuretic effect of muzolimine and the inhibition of Na+K+Cl- cotransport by urine from muzolimine-treated rats. These results suggest that the diuretic effect of muzolimine is due to the metabolism of muzolimine into an active compound which inhibits Na+K+Cl- cotransport after its secretion into the tubular lumen via a proximal pathway. The direct effect of muzolimine on Na+K+Cl- cotransport in MDCK cells was also tested: surprisingly, the inhibition of 86Rb influx was significant in the presence of muzolimine (IC50 = 1.44 microM). We show that this effect was due to the metabolism of muzolimine by these cells into an active compound.

Animals↗