Angiotensin actions in the kidney: renewed insight into the old hormone

Renin gene and angiotensin II AT1 receptor gene expression in the kidneys of normal and of two-kidney/one-clip rats

This study aimed to investigate the inter-relation between the angiotensin II (ANG II) AT1 receptor and renin gene expression in rat kidneys. To this end, renin mRNA levels and mRNA levels for AT1a and AT1b were assayed by RNase protection in the kidneys of normal rats, in animals treated with the AT1 antagonist losartan and in rats bearing 0.2-mm left renal artery clips for 2 days. In normal rats, we found a negative correlation between renin mRNA levels and AT1a receptor mRNA levels. Losartan led to a fourfold increase in renin mRNA levels without changing AT1 receptor mRNA levels. Unilateral renal artery clipping increased renin mRNA levels fourfold in the clipped kidney and suppressed renin mRNA levels in the contralateral kidneys. AT1 receptor mRNA levels were not changed in the contralateral intact kidneys, but were significantly decreased by 15-25% in the clipped kidneys. Renin mRNA levels were inversely correlated to AT1a mRNA levels in the clipped, but not in the contralateral, kidneys. Our findings suggest that the systemic activity of the renin angiotensin system has no regulatory influence on renal AT1 receptor gene expression. Renin mRNA levels in normal and in clipped kidneys appear to be negatively determined by the level of AT1a receptor gene expression. Thus modulation of AT1a receptor gene expression could be a pathway for indirect modulation of renin gene expression by ANG II. This conclusion is in agreement with the observation that AT1 receptor antagonists are powerful stimulators of the renin system.

Short-term and sustained renal effects of angiotensin II receptor blockade in healthy subjects

We investigated the short-term and sustained hormonal and renal effects of angiotensin II (Ang II) receptor blockade in normotensive healthy volunteers. Twenty-four subjects maintained on a fixed sodium diet were randomized to receive for 8 days a placebo or 10 or 50 mg doses of the Ang II antagonist irbesartan (SR 47436, BMS 186295) according to a double-blind, parallel group design. Plasma renin activity, plasma immunoreactive Ang II and aldosterone levels, blood pressure, renal hemodynamics, and urinary electrolyte excretion were measured for 8 hours after the first and eighth administration of each dose of irbesartan or placebo. Ang II receptor blockade with irbesartan induced a dose-dependent compensatory increase in plasma renin activity and plasma angiotensin levels and a significant decrease in plasma aldosterone levels. The compensatory rise in plasma renin activity and Ang II levels was more pronounced on day 8, reflecting a long duration of the blocking effect of irbesartan. Irbesartan induced small changes in blood pressure and did not significantly modify renal blood flow and glomerular filtration rate. However, a significant decrease in filtration fraction was observed during receptor blockade on days 1 and 8. The tubular effects of irbesartan were characterized by a dose-dependent increase in sodium and chloride excretions. Interestingly, the cumulative natriuretic response to Ang II receptor blockade was similar on days 1 and 8, suggesting that in these subjects, renal Ang II receptors are not blocked over 24 hours during repeated administration even though this antagonist has a long duration of action (t1/2 of 15 to 17 hours).(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular function and structure in the sodium-replete and sodium-deplete uninephrectomized spontaneously hypertensive rat: effect of blood pressure reduction, glomerular structure, and blood pressure reduction

To assess the effects of chronic dietary sodium restriction and blood pressure reduction on glomerular function and structure during the pathogenesis of hypertensive renal disease, experiments were conducted in uninephrectomized (UNX) spontaneously hypertensive rats (SHR) using the dihydropyridine calcium antagonist manidipine. Male SHRs underwent UNX at age 10-11 weeks and subsequently were assigned to one of four groups: sodium-replete (0.4%); sodium-replete and a predetermined antihypertensive dose of manidipine (20 mg/kg body weight); sodium-deplete (0.09%); and sodium-deplete and manidipine (20 mg/kg body weight). Twelve weeks later, renal morphologic and functional studies were performed. Sodium restriction had no significant effect on systolic blood pressure, but creatinine clearance and urinary protein excretion were decreased. Importantly, mean glomerular volume and the prevalence of mesangial expansion were lower with sodium restriction. This occurred in the presence of high concentrations of plasma and renal tissue angiotensin II. Manidipine significantly reduced systolic blood pressure in the sodium-replete and sodium-deplete UNX-SHRs. This therapy was not associated with significant changes in creatinine clearance and urinary protein excretion in the sodium-deplete or sodium-replete UNX-SHRs. The prevalence of mesangial expansion in the sodium-replete UNX-SHR was approximately 50% lower with manidipine. Plasma and renal tissue angiotensin II concentrations were not affected by the drug. In the sodium-deplete UNX-SHR, the prevalence of mesangial expansion was not reduced further by manidipine. However, plasma and renal tissue angiotensin II concentrations were increased significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Efficacy of intrarenal ACE-inhibition estimated from the renal response to angiotensin I and II in humans

Recent studies on the nature of the renin-angiotensin system (RAS) in animals have led to the concept that systemic and intrarenal RAS can be influenced to different degrees by angiotensin converting enzyme (ACE) inhibitors. Assessment of efficacy of intrarenal ACE inhibition by ACE inhibitors in humans is necessarily indirect and has not been reported. We therefore monitored the renal response to acute angiotensin (Ang) I infusion in volunteers taking 20 mg enalapril twice daily, and related the responses to the obtained increments in plasma Ang II levels. Ang I infusion rates of 4, 8, 16, and 32 pmol/kg/min caused gradual increments in plasma Ang I (maximal change from 26 +/- 18 to 578 +/- 120 pmol/liter, P < 0.05) and, despite treatment with enalapril, also of Ang II (from 3 +/- 1 to 29 +/- 5 pmol/liter, P < 0.05). This was associated with large reductions in renal plasma flow (paraaminohippurate clearance), filtration fraction, maximal urine flow, sodium excretion, lithium and uric acid clearance, and increments in mean arterial pressure and plasma aldosterone (P < 0.05 for each variable). Strong correlations existed between the changes in either variable and the increment in plasma Ang II. Infusions of Ang II at 1 and 4 pmol/kg/min in the same subjects caused comparable increments in plasma Ang II and had similar physiological effects as found during the Ang I infusion. Analysis of covariance of the changes in plasma Ang II and each of the measured variables revealed no differences between Ang I and Ang II infusions.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin as a renal growth promoting factor

The kidney has been traditionally considered to be one the pivotal organs involved in the systemic actions of the renin-angiotensin system (RAS) with renin produced in the juxtaglomerular apparatus and angiotensin II (ANG II) as a key player in the regulation of glomerular hemodynamics. However, many studies in the last decade, facilitated by a throughout molecular characterization of all elements of the RAS, have provided convincing evidence that the kidney exhibits a local RAS which may independently function from the systemic actions of the endocrine RAS. Moreover, even local distinct cell populations along the nephron possess all components of a functioning RAS. For example, proximal tubular cells express mRNA and protein for angiotensinogen, renin, and angiotensin converting enzyme (ACE). They bear different types of ANG II receptors with the appropriate signal transduction systems, and these cells also exhibit surface proteases like angiotensinase A which are required for the inactivation of ANG II. Moreover, recent studies in the isolated perfused kidney have clearly shown that proximal tubular cells produce considerable amounts of ANG II and these concentrations exceed approximately hundred times the systemic concentration of the peptide. Besides the well-known regulation of glomerular hemodynamics by contraction of the efferent glomerular arteriole and mesangium cells, ANG II influences transport and acidification processes in proximal and distal tubules. In addition, the octapeptide stimulates metabolic pathways like tubular gluconeogenesis and ammoniagenesis. Accumulating data over the last years derived from in vivo and in vitro studies have demonstrated that ANG II is also a growth factor for renal cells. For example, cell culture experiments have shown that the octapeptide stimulates proliferation or hypertrophy of mesangial cells. In contrast, proliferation of cultured proximal tubular cells is inhibited by ANG II and cellular hypertrophy of these cells is induced. Many studies have provided evidence that early mesangial proliferation/hypertrophy and tubular hypertrophy is a predecessor of the subsequent development of glomerulosclerosis and interstitial fibrosis, situations with irreversible morphological changes of the kidney's architecture leading finally to end-stage renal disease. Therefore, the identification of ANG II as a renal growth factor and a better understanding of its local intrarenal synthesis and growth stimulating effects on different cell types along the nephron may help to develop rational therapeutic interventions to prevent the progression of renal disease.

Remission of nephrotic range proteinuria in type I diabetes. Collaborative Study Group

The present study assessed the extent to which remission of nephrotic-range proteinuria occurred in patients with Type I diabetes enrolled in the Captopril Study, a placebo controlled multicenter clinical trial of captopril therapy in diabetic nephropathy. Of the 409 patients recruited into the Captopril Study, 108 had nephrotic-range proteinuria (> 3.5 g/24 hr) at entry in the Study (baseline). This group was the subject of the present study. Remission of nephrotic-range proteinuria was defined as follows: (1) Onset of the remission was taken as the date when proteinuria was first noted to be < or = 1.0 g/24 hr. (2) The reduction in proteinuria had to be sustained for a minimum of six months and until the end of the Captopril Study. (3) During the remission, the average of all 24 hour proteinuria measurements could not exceed 1.5 g. (4) Decline in renal function could not explain the reduced proteinuria. That is, the patient's serum creatinine during the entire period of observation in the Captopril Study had to remain at less than a doubling of the baseline serum creatinine. Remission of nephrotic-range proteinuria occurred in 7 of 42 patients assigned to captopril (16.7%, mean follow-up 3.4 +/- 0.8 years) and in 1 of 66 patients assigned to placebo (1.5%, mean follow-up 2.3 +/- 1.1 years; P = 0.005, comparing remission rate in captopril vs. placebo-treated patients).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of angiotensin II on isolated rabbit afferent arterioles

We examined the effects of angiotensin II (Ang II) on isolated rabbit afferent arterioles to assess the direct effect of Ang II at the resistance vessel level in the kidney. We microdissected the superficial afferent arteriole from the kidney of New Zealand White rabbits. The afferent arteriole was cannulated with a micropipette system, and the intraluminal pressure was set at 80 mmHg. Ang II did not change the lumen diameter of the afferent arterioles. After the afferent arterioles were pretreated with aspirin DL-lysine or indomethacin, Ang II (10(-7) M) caused transient vasoconstriction in the afferent arterioles. Ang II (10(-7) M) caused persistent constriction in the afferent arterioles pretreated with NG-nitro-L-arginine (10(-4) M). Physiological doses of Ang II decreased the lumen diameter of the isolated afferent arterioles pretreated with NG-nitro-L-arginine and aspirin DL-lysine. Dup753 (10(-6) M), an AT1-receptor antagonist, abolished the vasoconstrictor effects of Ang II. These findings suggest that the isolated rabbit afferent arteriole has AT1 receptors, and the vasoconstrictor response of Ang II is counteracted by vasodilatory prostaglandins and nitric oxide.

Modulation of glomerular hypertension defines susceptibility to progressive glomerular injury

The fawn-hooded rat constitutes a spontaneous model for chronic renal failure with early systemic and glomerular hypertension, proteinuria (UpV) and high susceptibility to development of focal and segmental glomerular sclerosis (FGS). It has been argued that uninephrectomy (UNX) accelerates the development of glomerular injury by aggravation of glomerular hypertension and by an independent effect to promote glomerular enlargement. The present study was performed to further delineate the importance of these parameters for the development of FGS. At the age of eight weeks male rats were UNX and randomly assigned to either control (CON), enalapril (ENA) or Nw-nitro L-arginine methyl ester (NAME) treatment. In all groups glomerular hemodynamic studies were performed four weeks post-UNX. Systemic blood pressure and UpV were monitored for 4 to 12 weeks post-UNX. Kidneys were then prepared for morphologic study. ENA treatment achieved control of both systemic and glomerular hypertension, maintenance of glomerular hyperfiltration and hyperperfusion, increased ultrafiltration coefficient(Kf), and long-term protection against UpV and FGS. NAME rats showed aggravation of both systemic and glomerular hypertension, decreased renal perfusion and filtration with reduced Kf, and high filtration fraction. The incidence of FGS in NAME and CON groups was similar at 8 and 12 weeks post-UNX, respectively. Glomerular enlargement was present in CON and ENA rats, but did not correlate with injury, while glomerular tuft size was lowest in NAME rats, which displayed prominent glomerular injury. Systemic blood pressure correlated strongly with glomerular capillary pressure. We conclude that systemic and glomerular hypertension govern the development of UpV and FGS.(ABSTRACT TRUNCATED AT 250 WORDS)

Posttransplant erythrocytosis: an enigma revisited

Posttransplant erythrocytosis (PTE) is an often-recognized but poorly understood complication of renal transplantation. Defined as a persistently elevated hematocrit (> 0.51), it occurs most commonly during the first 2 years posttransplant in hypertensive males with excellent allograft function. Its consequences are disputed, but may include increased risk of thromboembolic events. Traditionally, PTE has been thought to reflect excess erythropoietin production, of either native kidney or allograft origin, and to abate spontaneously with time. More recent data indicate that factors other than erythropoietin may be involved in the pathogenesis of PTE and that spontaneous resolution is relatively uncommon. Standard treatments have included serial phlebotomy and native kidney nephrectomy. It now appears that PTE also can be managed safely and effectively with converting enzyme inhibitors, a development that challenges our previous understanding of PTE and offers new avenues for investigating its pathogenesis.

Angiotensin II stimulates extracellular matrix protein synthesis through induction of transforming growth factor-beta expression in rat glomerular mesangial cells

Angiotensin II (Ang II) has been implicated in the development of progressive glomerulosclerosis, but the precise mechanism of this effect remains unclear. In an experimental model, we have shown previously that TGF-beta plays a key role in glomerulosclerosis by stimulating extracellular matrix protein synthesis, increasing matrix protein receptors, and altering protease/protease-inhibitor balance, thereby inhibiting matrix degradation. We hypothesized that Ang II contributes to glomerulosclerosis through induction of TGF-beta. Ang II treatment of rat mesangial cells in culture increased TGF-beta and matrix components biglycan, fibronectin, and collagen type I at both the mRNA and protein levels in a time- and dose-dependent manner. Saralasin, a competitive inhibitor of Ang II, prevented the stimulation. Ang II also promoted conversion of latent TGF-beta to the biologically active form. Coincubation of mesangial cells with Ang II and neutralizing antibody to TGF-beta blocked the Ang II-induced increases in matrix protein expression. Continuous in vivo administration of Ang II to normal rats for 7 d resulted in 70% increases in glomerular mRNA for both TGF-beta and collagen type I. These results indicate that Ang II induces mesangial cell synthesis of matrix proteins and show that these effects are mediated by Ang II induction of TGF-beta expression. This mechanism may well contribute to glomerulosclerosis in vivo.

Ontogenesis of sympathetic responsiveness in spontaneously hypertensive rats. II. Renal G proteins in male and female rats

Previously we have reported an increased renal alpha 1- and beta-adrenergic receptor expression in male spontaneously hypertensive rats that occurred ontogenetically in parallel with blood pressure elevation. However, increased receptor numbers were not accompanied by enhanced stimulation of inositol phosphate and cyclic AMP formation, respectively, indicating relative desensitization. We have now quantified alpha-subunits of the G proteins Gs (Gs short and Gs long), G(i), and Gq by immunoblotting and pertussis toxin-catalyzed ADP-ribosylation in renal membranes from 3-, 6-, 8-, and 28-week-old normotensive and spontaneously hypertensive male Wistar-Kyoto rats; additionally, 28-week-old female normotensive and spontaneously hypertensive rats were studied. During ontogenesis of male normotensive rats, Gs short increased, Gs long remained unchanged, and G(i) alpha and Gq alpha decreased. In adult normotensive rats no sex differences were detected for Gs short, Gs long, and G(i) alpha. When male rats from the normotensive and spontaneously hypertensive strains were compared, all G protein alpha-subunits were similar in the prehypertensive phase (3 weeks). In established hypertension (28 weeks), Gs long and Gq alpha were reduced, whereas Gs short and G(i) alpha remained unchanged. Gs long was also reduced during the development of hypertension (6 and 8 weeks), whereas Gs short and G(i) alpha were not consistently altered in this phase. The reduction in Gs long seen in male adult hypertensive rats was not detectable in female hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular prostaglandins modulate vascular reactivity of the downstream efferent arterioles

The balance of vascular resistance in afferent (Af-) and efferent arterioles (Ef-Arts) is a crucial factor that determines glomerular hemodynamics. We have recently reported that when Ef-Arts were perfused from the distal end of the Af-Art through the glomerulus (orthograde perfusion; OP), both angiotensin II (Ang II) and norepinephrine (NE) induced much weaker constriction than they did when Ef-Arts were perfused from the distal end (retrograde perfusion; RP). This difference was not affected by inhibiting synthesis of nitric oxide. In the present study, we tested the hypothesis that glomerular prostaglandins (PGs) may modulate vascular reactivity of the downstream Ef-Art. In addition, we examined the possible modulatory role of PGs in the Af-Art responses to Ang II or NE. Both Ang II and NE caused dose-dependent constriction of Ef-Arts with either OP or RP; however, the constriction was stronger in RP. At 10(-8) M, Ang II decreased Ef-Art diameter by 35 +/- 3.5% in OP (N = 9) compared to 73 +/- 3.9% in RP (N = 5), while 10(-6) M NE decreased the diameter by 25 +/- 3.6% in OP (N = 9) compared to 62 +/- 7.2% in RP (N = 5). Pretreatment with 5 x 10(-5) M indomethacin (Indo) did not alter basal diameter with either method of perfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced permselectivity in isolated perfused rat kidneys following small elevations of glomerular capillary pressure

A modified rat kidney preparation was used to explore how changes in hydrostatic pressure affect the permselective properties of the glomerular capillary bed. The maximally vasodilated kidneys of 18 rats were perfused with albumin solutions (16.7 g l-1) at different flow rates and hence arterial pressures (PA). One kidney in each rat was exposed to pressure elevations with the other kidney serving as a control perfused at constant PA of about 100 mmHg. Both the vascular resistance to flow and the glomerular filtration rate (GFR 34.6 +/- 2.9 ml min-1 100 g-1) were similar in the two kidneys at equal PA and remained constant throughout the experiment. The ratio of albumin clearance over GFR (theta) was initially around 0.4% at constant PA and gradually increased during 1.5 h to reach 0.7% at the end of the experiment. A direct increase of PA from 100 to 200 mmHg for 15 min resulted in a calculated increase of the effective glomerular filtration pressure gradient of 10-15 mmHg and in a two-fold increase of theta when measured at an identical PA of 100 mmHg. Albumin clearance was almost fully normalized within 20 min similar to that observed in e.g. skeletal muscle. However, the glomerular capillary barrier seemed to be far more sensitive to elevations of hydrostatic pressure than other capillary walls which require capillary pressure increments of 60 mmHg in order to induce similar reversible changes in permeability. Therefore, we conclude that an elevated PGC per se induces changes of glomerular permselectivity, which may have important pathophysiological implications during conditions of proteinuria.

Angiotensin-converting enzyme inhibition partially prevents diabetic organomegaly

The present study was conducted to evaluate whether captopril prevents the organomegaly and accumulation of matrix proteins that normally accompanies the diabetic state. The following groups of rats were studied: normal rats, normal rats treated with captopril (30 mg/kg/d orally), streptozotocin diabetic rats, and diabetic rats treated with captopril. All rats were killed at 10 weeks for histologic and morphometric evaluation of tissues. Compared with the normal rats, the diabetic rats demonstrated significant hepatomegaly, nephromegaly, and cardiomegaly, and the increase in organ size was directly related to increasing levels of protein glycosylation. The development of organomegaly was partially prevented by captopril. We determined by morphometry that the hepatomegaly seen in the diabetic rats was due to an increase in cell size and number, while the nephromegaly seen in the diabetic rats was due to an increase in tubular and glomerular cell size and is associated with glomerular hypertrophy. Captopril prevented the development of hepatic and renal cell hypertrophy and glomerular hypertrophy. These effects of captopril were not associated with detectable changes in body weight or levels of glucose, protein glycosylation, glycosuria, or renal histologic changes secondary to glycosuria. The diabetic rats demonstrated significant glomerular mesangial matrix expansion, and captopril treatment partially prevented that expansion. In conclusion, captopril prevents, in part, the development of organomegaly in diabetic rats, and this effect is due mainly to the prevention of the development of cellular hypertrophy. The present findings are most consistent with a direct effect of captopril on cell metabolism during diabetes mellitus.

Ontogeny of renin and AT1 receptor in the rat

The enzyme renin and the angiotensin II (Ang II), subtype I receptor (ATI) are developmentally regulated in a tissue-specific manner. In early life, renin is expressed widely along the renal vasculature. As maturation progresses, there is a decrease in renin mRNA levels and a shift in the localization of renin close to the glomerulus. In addition, in the newborn rat, the number of renin-secreting cells is higher than in the adult rat. Exposure of neonatal and adult cells to Ang II results in a decrease of similar magnitude in the number of renin-secreting cells. These findings suggest that the high levels of renin observed in immature animals are due to increased renin synthesis and release rather than to a blunted response to Ang II. Expression of the ATI gene is also developmentally regulated in a tissue-specific manner. With maturation, ATI mRNA levels decrease in the kidney while they increase in the liver. The localization of ATI transcripts in precursor cells of the nephrogenic cortex suggests a role for this receptor in nephron growth and development. Inhibition of ATI with DUP753 results in delayed kidney and somatic growth and in increased renin mRNA levels and recruitment of renin-containing cells. These observations suggest that Ang II exerts a tonic negative feedback on renin gene expression via the ATI receptor subtype. Further studies are necessary to delineate the molecular and cellular signals mediating these developmental changes.

Protein kinase C and calcium channel activation as determinants of renal vasoconstriction by angiotensin II and endothelin

The mechanisms mediating renal microvascular constriction induced by angiotensin II (Ang II) and endothelin (ET) have not been fully established. In the present study, we have determined the effects of isradipine, a dihydropyridine calcium antagonist, on Ang II- or ET-induced constriction of afferent arterioles (AAs) and efferent arterioles (EAs) using the isolated perfused hydronephrotic kidney. Ang II (0.3 nmol/L) and ET (0.3 nmol/L) constricted AAs by 36 +/- 2% and 29 +/- 3%, respectively. Isradipine reversed AA constriction induced by both peptides. However, Ang II-induced AA constriction was more sensitive to isradipine than ET-induced constriction (half-maximal inhibitory concentration [IC50], 1.2 +/- 0.2 nmol/L [n = 12] versus 170 +/- 65 nmol/L [n = 19]; P < .01). The sensitivity of Ang II-induced AA constriction to isradipine was identical to that of KCI-induced AA constriction (IC50, 4.2 +/- 0.9 nmol/L; n = 12). Pretreatment with staurosporine (50 nmol/L), a protein kinase C inhibitor, enhanced the sensitivity of ET-induced AA constriction to isradipine (4.3 +/- 1.7 nmol/L, n = 14), rendering it identical to that of KCl-induced AA constriction. Ang II and ET decreased EA diameter by 26 +/- 2% (n = 12) and 12 +/- 2% (n = 8), respectively. In contrast to AA constriction, EA constriction induced by both peptides was relatively refractory to isradipine.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships among alterations in renal membrane sodium transport, renin and aminopeptidase M activities in genetic hypertension

Rats of the Milan Hypertensive Strain (MHS) may be considered a useful model for understanding the genetic molecular mechanism underlying a primary form of hypertension in at least a subgroup of patients. Many differences between MHS and its normotensive control strain (MNS) were found at the organ, cellular and biochemical level. In the present investigation renal cell membrane proteins (BBMV) were analysed by two-dimensional electrophoresis and a difference between MHS and MNS was shown in a polypeptide of 32 kDa, subsequently identified as the C-terminal fragment of aminopeptidase M (APM). The activity of the enzyme was higher in MHS. Genetic relationships between this enzyme and the other biochemical cellular abnormalities of MHS, namely sodium transport in BBMV and renin activity in kidney cortex were investigated in MHS, MNS and in two inbred recombinant strains. This analysis showed that faster sodium transport, low kidney levels of renin and hypertension, but not differences in two-dimensional electrophoretic pattern and in aminopeptidase M activity, cosegregated in recombinant strains. These results are consistent with the hypothesis that the faster sodium transport can be considered a primary cellular abnormality responsible for hypertension in MHS and that the aminopeptidase difference is not involved in the cellular abnormalities.

Cellular expression of angiotensin type-1 receptor mRNA in the kidney

Angiotensin II has multiple renal effects that are important in the regulation of renal hemodynamics and electrolyte secretion, and binding sites for angiotensin II have been demonstrated in different cells of the kidney. In the present study the cellular localization of mRNA for the angiotensin type 1 (AT1) subtype of the angiotensin II receptor was studied in adult rat kidney using a cRNA probe and in situ hybridization. Strong labeling was demonstrated in tubule cells of the inner and outer stripe of the outer medulla. In emulsion-dipped sections, counter-stained with hematoxylin-eosin, labeling was identified in segment S3 of proximal tubules and in the thick ascending limb of loop of Henle (mTAL). The results suggest expression of AT1-receptor mRNA with a distinct compartmentalization within the nephron.

Angiotensin blockade and the progression of renal damage in the spontaneously hypertensive rat

The pathophysiological role of angiotensin II in the development of renal sclerosis was investigated in 5/6-nephrectomized, 12-week-old male spontaneously hypertensive rats. After 1 week of a control period, nephrectomized rats received one of the following treatments for 4 weeks: the selective nonpeptide angiotensin II type 1 receptor antagonist TCV-116 (1 mg/kg per day), the angiotensin converting enzyme inhibitor delapril (30 mg/kg per day), hydralazine (15 mg/kg per day), or vehicle. Urinary protein and albumin excretions and systolic blood pressure were determined every week. Rats with reduced renal mass treated with vehicle had a poor survival rate (30%). Although TCV-116, delapril, and hydralazine treatment significantly improved the survival rate for 4 weeks, hydralazine failed to improve proteinuria and albuminuria as well as the decline in renal function compared with delapril or TCV-116. Histological examination revealed that both TCV-116 and delapril protected glomeruli from sclerosis, whereas hydralazine did not improve histological findings (5%, 7%, and 30% of glomeruli were affected, respectively). These results indicate that angiotensin II plays a dominant role through its type 1 receptor in the pathogenesis of renal deterioration by hypertension.

Angiotensin II local hyperreactivity in the progression of IgA nephropathy

Immunologic and hemodynamic factors are likely to work in synergism in the progression of immunoglobulin A nephropathy (IgAN) toward sclerosis. The local activation of the renin-angiotensin system may be one the most relevant mechanisms. We investigated the hemodynamic effects of the acute administration of angiotensin-converting enzyme inhibitor (ACEI) (captopril 50 mg). The glomerular filtration rate (GFR) and the effective renal plasma flow (ERPF) were measured by 51Cr-EDTA and 125I hippurate clearances. The correspondent filtration fractions (FFs) in basal conditions and after administration of ACEI were calculated, then the changes in FF (delta FF and % delta FF) were determined. We studied 27 IgAN patients. Eighteen patients had normal renal function (GFR, 112 +/- 19 mL/min/1.73 m2) and nine had moderate renal impairment (GFR, 54 +/- 13 mL/min/1.73 m2). Sixteen patients had proteinuria > or = 0.5 g/d. In addition, 12 glomerulonephritis control cases and eight healthy subjects were investigated. After the administration of ACEI in healthy subjects we observed slight modifications in the GFR, a significant increase in the ERPF (P < 0.005), and a significant decrease in FF (P < 0.04). Similarly, in IgAN patients with normal renal function the GFR increased slightly, the ERPF increased significantly (P < 0.01), and there was a decrease in FF (P < 0.01). The delta FF and % delta FF values were not significantly different from those found in the controls. In patients with initial renal failure GFR remained unchanged, ERPF increased significantly (P < 0.005), and FF significantly decreased (P < 0.004). However, the changes in delta FF and % delta FF were significantly greater than those found in healthy controls (P < 0.01) and in IgAN patients with normal renal function (P < 0.001). IgAN patients with proteinuria levels > or = 0.5 g/d showed greater changes in delta FF and % delta FF after the administration of ACEI than patients with proteinuria levels lower than 0.5 g/d (P < 0.003 and P < 0.04, respectively) or proteinuric control cases (P < 0.05 and P < 0.01, respectively). This different response in proteinuric and nonproteinuric patients was evident even when the analysis was limited to the subgroup of IgAN patients with normal renal function. The decrease in FF consequent to an increase in the ERPF after the administration of ACEI suggests a local hyperactivity of the renin-angiotensin system in some cases of IgAN.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Endothelium-derived relaxing factor/nitric oxide modulates angiotensin II action in the isolated microperfused rabbit afferent but not efferent arteriole

It has been reported that sensitivity to angiotensin II (Ang II) is higher in efferent (Ef) than afferent (Af) arterioles (Arts). We tested the hypothesis that this is due to arteriolar differences in the interaction between Ang II and endothelium-derived relaxing factor/nitric oxide (EDNO). Rabbit Af-Arts with glomerulus intact were microperfused in vitro at a constant pressure. Ef-Arts were perfused from the distal end of either the Af-Art (orthograde perfusion) or the Ef-Art (retrograde perfusion) to eliminate influences of the Af-Art or glomerulus, respectively. Ang II did not alter Af-Art luminal diameter until the concentration reached 10(-9) M, which decreased the diameter by 11 +/- 2.6% (n = 11; P < 0.002). In contrast, Ef-Arts became significantly constricted at concentrations as low as 10(-11) M with either perfusion. Surprisingly, the decrease in Ef-Art diameter at 10(-10), 10(-9), and 10(-8) M was significantly greater with retrograde perfusion (44 +/- 6.9%, 70 +/- 5.6%, and 74 +/- 4.1%, respectively; n = 5) than with orthograde perfusion (16 +/- 4.2%, 25 +/- 2.9%, and 35 +/- 3.5%; n = 9). ENDO synthesis inhibition with 10(-4) M nitro-L-arginine methyl ester (L-NAME) decreased the diameter to a greater extent in Af-Arts (22 +/- 3.0%; n = 11) compared to Ef-Arts with either orthograde (9.5 +/- 2.3%; n = 8) or retrograde perfusion (1.2 +/- 2.1%; n = 6). With L-NAME pretreatment, Af-Art constriction induced by 10(-10) M (14 +/- 4.0%, n = 9) and 10(-9) M Ang II (38 +/- 3.9%) was significantly greater compared to nontreated Af-Arts. In contrast, L-NAME pretreatment had no effect on Ang II-induced constriction in Ef-Arts with either perfusion. In conclusion, this study demonstrates higher sensitivity of Ef-Arts to Ang II, particularly with retrograde perfusion. Our results suggest that EDNO significantly modulates the vasoconstrictor action of Ang II in Af-Arts II but not Ef-Arts, contributing to the differential sensitivity to Ang II.

Clinical pharmacokinetics of angiotensin converting enzyme (ACE) inhibitors in renal failure

Arterial hypertension occurs frequently in patients with chronic renal failure. Antihypertensive treatment of arterial hypertension with angiotensin converting enzyme (ACE) inhibitors has been shown to be effective with a low incidence of adverse effects compared with other drug classes. Furthermore, treatment with ACE inhibitors may slow the progression of renal function impairment in certain groups of patients, such as those with diabetes. Most ACE inhibitors are prodrugs which are converted by hepatic esterolysis to an active diacid metabolite. Only captopril and lisinopril have sufficient oral bioavailability and are given as active drugs. ACE inhibitors can be subdivided into 3 classes with regard to the active group: the majority of ACE inhibitors are carboxyl-containing drugs, a new class of ACE inhibitors possess a phosphoryl-group and captopril and related compounds are sulfhydryl-containing drugs. The predominant elimination pathway of ACE inhibitors is excretion via the kidneys. Therefore, renal insufficiency is associated with reduced elimination of most ACE inhibitors and, thus, altered pharmacokinetic properties. This is most evident in chronic renal failure when glomerular filtration rates (GFR) are < 30 to 40 ml/min (1.8 to 2.4 L/h). As renal clearance decreases, the peak plasma concentration and area under the plasma concentration-time curve of the active drugs or diacids are increased and time to peak concentrations and half-life are prolonged. However, there are large between-drug differences in the changes in pharmacokinetic parameters, resulting in different degrees of drug accumulation after consecutive administration. This leads, for example, to high accumulation rates for drugs such as lisinopril, or cilazaprilat. In contrast, fosinopril, which is also excreted to a large extent by the hepatobiliary pathway, does not seem to accumulate in renal failure. In general, pharmacokinetics and conversion of prodrugs seem to be slightly affected in chronic renal failure; however, these changes do not appear to be clinically relevant. Efficiency of clearance for prodrugs or active drugs and their respective metabolites by haemodialysis or peritoneal dialysis varies considerably. For some ACE inhibitors, such as captopril or enalapril, the high elimination fraction by haemodialysis necessitates a supplemental dose after dialysis. Other ACE inhibitors, such as quinapril or cilazapril, are only poorly eliminated by haemodialysis or peritoneal dialysis. Dosage recommendations for treatment with ACE inhibitors in chronic renal failure depend on the specific pharmacokinetic properties of the various agents. For most ACE inhibitors, dosage adjustment is recommended in moderate and severe impairment of renal function, with resultant dosages being 25 to 50% of those recommended for patients with normal renal function.

An evaluation of the renal protective effect of manidipine in the uninephrectomized spontaneously hypertensive rat

The effects of calcium antagonism on the development and progression of renal disease are controversial. To address this problem, studies were performed on young, uninephrectomized spontaneously hypertensive rats (SHRs) with the dihydropyridine calcium antagonist, manidipine, to assess its effect on the early pathogenesis of focal glomerulosclerosis. Male SHRs underwent uninephrectomy at age 10 to 11 weeks and were subsequently assigned to no treatment (control), a predetermined subvasodepressor (low) dose of manidipine (2.5 mg/kg body weight), or a predetermined antihypertensive (high) dose of manidipine (20 mg/kg body weight). All animals received a diet containing 0.4% sodium and 23% protein. Serial determinations of body weight, systolic tail cuff pressure, and 24-hour urinary excretion of creatinine, sodium, and protein (UprotV) were made at 1- to 6-week intervals, for a total treatment period of 12 weeks. In final experiments plasma was obtained for creatinine, angiotensin I, and angiotensin II determinations, and renal tissue was harvested for histologic and morphometric analysis. Compared with the untreated control, low-dose manidipine therapy had no effect on body weight, systolic blood pressure, creatinine clearance, UprotV, renal histologic findings, glomerular volume, or plasma angiotensin I or II concentrations. In contrast, high-dose manidipine therapy decreased systolic blood pressure from 194 +/- 3 to 160 +/- 4 mm Hg (p < 0.01). Creatinine clearance and UprotV were unchanged. Although body weight was not different, kidney weight was higher. However, mean glomerular volume was lower. More importantly, the prevalence of mesangial expansion with proliferation was lower: 6.7% (control) versus 2.8% (high-dose manidipine) (p < 0.01). Finally, plasma angiotensin I and angiotensin II concentrations did not differ.(ABSTRACT TRUNCATED AT 250 WORDS)

Ontogeny of type 1 angiotensin II receptor gene expression in the rat

To determine whether the expression of the type 1 angiotensin II receptor (AT1) gene is developmentally regulated and whether the regulation is tissue specific, AT1 mRNA levels were determined by Northern blot analysis in livers and kidneys from fetal, newborn, and adult rats, using a 1133-bp rat AT1 cDNA. In the liver, AT1 mRNA levels increased fivefold from 15 d gestation to 5 d of age. Liver AT1 mRNA levels at 5 d of age were similar to those of adult rats. In the kidney, AT1 mRNA levels were higher in immature than in adult animals. The intrarenal distribution of AT1 mRNA was assessed by in situ hybridization to a 35S-labeled 24 residues oligonucleotide complementary to rat AT1 mRNA. In the adult, AT1 mRNA was present in glomeruli, arteries, and vasa recta, whereas in the newborn AT1 mRNA was observed also over the nephrogenic area of the cortex. We conclude that: (a) fetal kidney and liver express the AT1 gene; (b) the AT1 gene expression is developmentally regulated in a tissue-specific manner; (c) during maturation, localization of AT1 mRNA in the kidney shifts from a widespread distribution in the nephrogenic cortex to specific sites in glomeruli, arteries, and vasa recta, suggesting a role for the angiotensin receptor in nephron growth and development.

Captopril acutely lowers albuminuria in normotensive patients with diabetic nephropathy

Angiotensin-converting enzyme (ACE) inhibitors decrease albuminuria in patients with diabetic nephropathy. To study the change in albuminuria in relation to changes in systemic and renal hemodynamics, nine normotensive patients with type 1 (insulin-dependent) diabetes mellitus and persistent proteinuria were given a single oral dose of 25 mg of the ACE inhibitor captopril. Blood pressure, glomerular filtration rate (GFR), effective renal plasma flow (ERPF), and albumin excretion rate (AER) were measured in two periods of 40 minutes before and in four periods of 40 minutes after administration of captopril. A constant water diuresis was maintained. Blood pressure did not decrease significantly (130/79 +/- 4/3 v 124/74 +/- 4/3 mm Hg; mean +/- SEM), median AER decreased from 403 (interquartile range [IQR], 812) micrograms/min to 333 (707) micrograms/min (P < 0.01). GFR did not change (123 +/- 13 v 117 +/- 14 mL/min), but ERPF increased significantly from 609 +/- 56 to 714 +/- 55 mL/min (P < 0.01). Consequently, the filtration fraction (FF; quotient of GFR and ERPF) decreased from 0.20 +/- 0.014 to 0.17 +/- 0.014 (P < 0.01). A strong correlation was found between the decrease of AER and the decrease of FF (rs = 0.75; P < 0.02). No correlation was found between the decrease in AER and changes in GFR or blood pressure. In the normotensive patient with diabetic nephropathy, captopril causes an acute reduction of AER, which is probably mediated by a lowering of the intraglomerular pressure.

Angiotensinase A (aminopeptidase A): properties of chromatographically purified isoforms from human kidney

Angiotensin-II-cleaving angiotensinase A (aminopeptidase A, E.C. 3.4.11.7, ATA) plays an important role in glomerular haemodynamics. the pathophysiology of essential arterial hypertension and the induction of vascular disorders. In order to study biochemical and immunological properties of ATA, two isoforms (I and II) of the glycoprotein were isolated for the first time from human kidney cortex. Kidney cortex homogenate, digested with bromelain, was fractionated by ammonium sulphate precipitation and subsequent hydrophobic interaction chromatography, using a fast protein liquid chromatographic (FPLC) system. By anion-exchange FPLC (Mono Q column), the isoforms of ATA were eluted in two distinct peaks and were further purified by size-exclusion FPLC and preparative polyacrylamide gel electrophoresis. Biochemical, immunological and immunohistological characterization disclosed differences in the intrarenal localization, glycosylation Michaelis constant and apparent molecular mass (native and sodium dodecyl sulphate gel electrophoresis) but similar properties in the double-immunodiffusion technique. Polyclonal rabbit antibodies, raised against ATA isoforms I and II, precipitated an analogous antigen in urine from patients with renal tubular damage.

Characterization of an angiotensin type-1 receptor partial cDNA from rat kidney: evidence for a novel AT1B receptor subtype

We sought to determine if multiple forms of mRNA for the angiotensin type-1 (AT1) receptor could be detected in rat kidney using the polymerase chain reaction (PCR) procedure. Amplification of rat kidney cDNA with oligonucleotide primers derived from the second and sixth transmembrane domains of the rat AT1 receptor yielded a single cDNA fragment 528bp in size. Sequence analysis indicated, however, that the cDNA fragment was a mixture of two highly similar gene products: the first cDNA was identical to the previously cloned AT1 receptor (termed here AT1A) whereas the second cDNA (termed here AT1B) was 92% identical at the nucleotide level and 96% identical at the amino acid level. Nucleotide substitutions were dispersed throughout the cDNA and 80% (33 of 41) were conservative. Significant levels of AT1A and AT1B mRNA were detected by PCR amplification of kidney poly(A)+ RNA and restriction enzyme analysis. These results indicate that at least two distinct AT1 receptor genes are expressed in rat kidney.

Blood pressure, angiotensin-converting enzyme (ACE) inhibitors, and the kidney

Angiotensin II plays an important role in the kidney by regulating renal flow, glomerular filtration rate, mesangial cell function, and sodium reabsorption. Blockade of the renin-angiotensin system has powerful effects on kidney function. Studies in animal models of renal failure suggest that converting enzyme inhibitors slow down the inevitable progression of the renal failure. This could be in part due to their effect on reducing glomerular pressure or by reducing glomerular hypertrophy. In patients with malignant hypertension, diabetic nephropathy, and other causes of renal failure, preliminary evidence suggests that lowering the blood pressure with angiotensin-converting enzyme (ACE) inhibitors may possibly carry some other benefits compared with other blood pressure lowering regimens. However, single drug therapy is rarely sufficient to control blood pressure in these patients. Further properly controlled randomized trials should give a clear indication of whether any particular class of drug has any advantage in slowing down the progressive renal impairment for a given lowering of blood pressure. In patients with renovascular hypertension ACE inhibitors are effective drugs in lowering blood pressure. However, in certain settings they may cause a reversible decline in renal function.