Novel markers of graft outcome in a cohort of kidney transplanted patients: a cohort observational study.

Renal biopsy (RBx) informs about kidney transplantation (KTx) prognosis. In our observational study the prevalence of histological anomalies and the prognostic role of CD45, vimentin (VIM) and periostin (POSTN) in KTx-RBx have been evaluated. One hundred forty-six KTx-RBx (2009-2012) were analysed for general histology and in immunohistochemistry for CD45, VIM and POSTN. Clinical data of the 146-KTx patients were collected at the RBx time (T0), 6 and 12 months before and after RBx. Follow-up time was 21 ± 14 months. Glomerulosclerosis was 20% glomeruli/biopsy. Tubular atrophy (TA), Interstitial infiltrate (I-Inf) and interstitial fibrosis (IF) were slight in 21-18% and 25%, moderate in 22-30% and 26% and severe in 30-18% and 28% of patients. Fifty-eight percent of patients had lesions compatible with IF-TA. CD45, VIM and POSTN correlated to each-other and to TA, I-Inf and IF. VIM and POSTN correlated to GS. CD45 and VIM correlated directly to renal function (RF) and 25(OH)VitD, while POSTN inversely to 25(OH)VitD. Thirty patients restarted dialysis (HD+). HD+ had lower T0-eGFR, and higher CD45, VIM and POSTN than HD-. POSTN resulted the strongest in discriminate for HD+ . CD45, VIM and POSTN correlate to each-other and predict graft outcome. POSTN was the strongest in discriminate for HD+. 25(OH)VitD might influence inflammation and fibrosis in KTx.

Reversal of renal disease: is it enough to inhibit the action of angiotensin II?

Over the last years, evidence emerged demonstrating that the progression of renal fibrosis is reversible in experimental models. The present review summarizes the new insights concerning the mechanisms of progression and regression of renal disease and examines this novel evidence under the light of feasibility and transfer to human nephropathies. The involved mechanisms are discussed with particular emphasis on the fibrotic role of vasoactive peptides such as angiotensin II and endothelin, and growth factors such as transforming growth factor beta (TGFbeta). The possibility of regression is introduced by presenting the in vivo efficiency of anti-hypertensive treatments and of systems that antagonize the fibrogenic action of TGFbeta such as bone morphogenic protein-7 (BMP-7) and hepatocyte growth factor. Finally, we provide a brief description of the promising future directions and clinical considerations about the applications of the experimental data to humans.

Regulation of angiotensin II receptor AT1 subtypes in renal afferent arterioles during chronic changes in sodium diet.

Studies determined the effects of chronic changes in sodium diet on the expression, regulation, and function of different angiotensin II (ANG II) receptor subtypes in renal resistance vessels. Rats were fed low- or high-sodium diets for 3 wk before study. Receptor function was assessed in vivo by measuring transient renal blood flow responses to bolus injections of ANG II (2 ng) into the renal artery. ANG II produced less pronounced renal vasoconstriction in rats fed a low- compared with high-sodium diet (16% vs. 56% decrease in renal blood flow, P < 0.001). After acute blockade of ANG II formation by iv enalaprilat injection in sodium-restricted animals, ANG II produced a 40% decrease in renal blood flow, a level between untreated dietary groups and less than high salt diet. Intrarenal administration of angiotensin II receptor type 1 (AT1) receptor antagonists losartan or EXP-3174 simultaneously with ANG II caused dose-dependent inhibition of ANG II responses. Based on maximum vasoconstriction normalized to 100% ANG II effect in each group, AT1 receptor antagonists produced the same degree of blockade in all groups, with an apparent maximum of 80-90%. In contrast, similar doses of the angiotensin II receptor type 2 (AT2) receptor ligand CGP-42112 had only a weak inhibitory effect. In vitro equilibrium-saturation 125I-ANG II binding studies on freshly isolated afferent arterioles indicated that ANG II receptor density was lower in the low- vs. high-sodium animals (157 vs. 298 fmol/mg, P < 0.04); affinity was similar (0.65 nM). Losartan and EXP-3174 displaced up to 80-90% of the ANG II binding; fractional displacement was similar in both diet groups. In contrast, the AT2 receptor analogues PD-123319 and CGP-42112 at concentrations < 10(-6) M had no effect on ANG II binding. RT-PCR assays revealed the expression of both angiotensin II receptor type 1A (AT(1A)) and angiotensin II receptor type 1B (AT(1B)) subtypes in freshly isolated afferent arterioles, while there was very little AT2 receptor expression. Total AT1 receptor mRNA expression was suppressed by low sodium intake to 66% of control levels, whereas it was increased to 132% of control by high-sodium diet, as indicated by ribonuclease protection assay. Receptor regulation was associated with parallel changes in AT(1A) and AT(1B) expression; the AT(1A)/AT(1B) ratio was stable at 3.7. We conclude that AT1 receptors are the predominant ANG II receptor type in renal resistance vessels of 7-wk-old rats. Chronic changes in sodium intake caused parallel regulation of expression and amount of receptor protein of the two AT1 receptor genes that modulate receptor function and altered reactivity of renal vessels to ANG II.

Nitric oxide inhibition induces early activation of type I collagen gene in renal resistance vessels and glomeruli in transgenic mice. Role of endothelin.

Hypertension is often associated with the development of nephroangio- and glomerulo-sclerosis. This pathophysiological process is due to increased extracellular matrix protein, particularly type I collagen, accumulation. This study investigated whether nitric oxide (NO) synthesis is involved in the mechanism(s) regulating activation of the collagen I gene in afferent arterioles and glomeruli. Experiments were performed on transgenic mice harboring the luciferase gene under the control of the collagen I-alpha2 chain promoter [procolalpha2(I)]. Measurements of luciferase activity provide highly sensitive estimates of collagen I gene activation. NO synthesis was inhibited by NG-nitro-L-arginine methyl ester (L-NAME) (20 mg/kg per day) for a period of up to 14 wk. Systolic blood pressure was increased after 6 wk of treatment (117+/-2 versus 129+/-2 mmHg, P < 0.01) and reached a plateau after 10 wk (around 160 mmHg). Luciferase activity was increased in freshly isolated afferent arterioles and glomeruli as early as week 4 of L-NAME treatment (150 and 200% of baseline, P < 0.01, respectively). The activation of procolalpha2(I) became more pronounced with time, and at 14 wk increased four- and tenfold compared with controls in afferent arterioles and glomeruli, respectively (P < 0.001). In contrast, luciferase activity remained unchanged in aorta and heart up to 8 wk and was increased thereafter. Increased histochemical staining for extracellular matrix deposition, and particularly of collagen I, was detected in afferent arterioles and glomeruli after 10 wk of L-NAME treatment. This fibrogenic process was accompanied by an increased urinary excretion rate of endothelin. In separate experiments, the stimulatory effect of L-NAME on collagen I gene activation was abolished when animals were treated with bosentan, an endothelin receptor antagonist. Similarly, bosentan reduced the increased extracellular matrix deposition in afferent arterioles and glomeruli during NO inhibition. Interestingly, bosentan had no effect on the L-NAME- induced increase of systolic pressure. These data indicate that NO inhibition induces an early activation of the collagen I gene in afferent arterioles and glomeruli. This activation in the kidney precedes the increase in blood pressure and the procolalpha2(I) activation in heart and aorta, suggesting a specific renal effect of NO blockade on collagen I gene expression that is independent of increased blood pressure and, at least partly, mediated through stimulation of the endothelin receptor. Use of procolalpha2(I) transgenic mice provides a novel and efficient model to study the pathophysiological mechanism(s) regulating renal fibrosis.

[Renal hemodynamics and development of renal fibrotic lesions during hypertension]. / Dissociation entre l'hémodynamique rénale et les lésions histologiques rénales induites par l'hypertension artérielle.

Hypertension is frequently associated with the development of renal fibrosis leading to chronic renal failure. The objective of the present study was to evaluate the role of blood pressure and renal hemodynamics on the development of renal lesions during hypertension. To this end, rats were treated with a NO synthase inhibitor, L-NAME, for 4 weeks. At this time point, systolic blood pressure reached 170 mmHg, renal blood flow dropped to 3.3 +/- 0.7 ml/min and kidneys displayed glomerular and tubulo-interstitial lesions as evidenced by histological analysis. Thereafter, L-NAME treatment was combined with an AT1 receptor antagonist, losartan (30 mg/kg/d), for an additional period of 4 weeks. Treatment with losartan for 4 additional weeks did not significantly modify hypertension (168 mmHg) either the degree of tubulo-interstitial lesions; in contrast, a significant regression of ischemic and sclerotic glomerular lesions was observed. In parallel, renal blood flow was significantly improved by losartan (5.2 +/- 0.8 ml/min). In addition a negative correlation was observed between renal blood flow and index of glomerulosclerosis (r = -0.82), whereas tubulo-intarstitial damage was positively correlated to systemic pressure (r = 0.93). In conclusion, inhibition of the local effects of angiotensin II alleviates the fall of renal blood flow consecutive to NO deficiency and reduces the morphological and functional lesions of glomeruli, independently of the changes in blood pressure. In contrast, tubulo-interstitial lesions are not correlated with the levels of renal blood flow and do not regress with the blockade of AT1 receptors when rats remain hypertensive.

Vascular endothelin-1 gene expression and synthesis and effect on renal type I collagen synthesis and nephroangiosclerosis during nitric oxide synthase inhibition in rats.

BACKGROUND: The progression of hypertension during NO deficiency is associated with renal vascular fibrosis due to increased extracellular matrix (mainly collagen I) formation. The purpose of the present study was to investigate whether endothelin-1 (ET-1) is involved in this pathophysiological process. METHODS AND RESULTS: Treatment of rats for 4 weeks with the NO synthase inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) 50 mg. kg-1. d-1 increased systolic blood pressure to 159+/-12 mm Hg. In animals treated with L-NAME, histological evaluation of renal sections revealed an increased formation of extracellular matrix (Masson's trichrome), and specifically of collagens (Sirius red). A part of this fibrosis was attributed to abnormal collagen I presence, because mRNA expression of the collagen I alpha1 chain (reverse transcription-polymerase chain reaction) and procollagen I formation (radioimmunoassay) were increased 3- and 2.5-fold, respectively, in the renal resistance vessels of hypertensive animals. In subsequent experiments, we examined whether ET-1 was involved in activation of collagen I formation. mRNA expression (RNase protection assay) of preproET-1 and ET-1 content (radioimmunoassay) were 10-fold and 3-fold increased, respectively, in renal microvessels of rats treated with L-NAME. Interestingly, in these vessels, ET-1 (immunostaining) was colocalized with sudanophilic lesions. Bosentan, an ET receptor antagonist (20 mg. kg-1. d-1), coadministered with L-NAME canceled the increased mRNA expression and synthesis of collagen I and attenuated the severity of renal vascular lesions without affecting L-NAME-induced high blood pressure. CONCLUSIONS: These data demonstrate that ET-1 synthesis is increased in renal microvessels when NO production is suppressed. In this model of hypertension, ET-1 is a major activator of collagen I formation in renal resistance vessels and participates in the development of renal fibrosis without affecting systolic blood pressure.

Angiotensin II activates collagen type I gene in the renal vasculature of transgenic mice during inhibition of nitric oxide synthesis: evidence for an endothelin-mediated mechanism.

BACKGROUND: Hypertension is frequently associated with renal vascular fibrosis. The purpose of this study was to investigate whether angiotensin II (Ang II) is involved in this fibrogenic process. METHODS AND RESULTS: Experiments were performed on transgenic mice harboring the luciferase gene under the control of the collagen I-alpha(2) chain promoter [procolalpha(2)(I)]. Hypertension was induced by chronic inhibition of NO synthesis (N(G)-nitro-L-arginine methyl ester, L-NAME). Procolalpha(2)(I) activity started to increase in the renal vasculature after 4 weeks of L-NAME treatment (P<0.01) and at 14 weeks reached 3- and 8-fold increases over control in afferent arterioles and glomeruli, respectively (P<0.001). Losartan, an AT(1) receptor antagonist, given simultaneously with L-NAME prevented the increase of procolalpha(2)(I) levels and attenuated the development of renal vascular fibrosis without normalizing systolic pressure increase. Because we found previously that endothelin mediated renal vascular fibrosis in the L-NAME model, the interaction between Ang II, endothelin, and procolalpha(2)(I) was investigated in ex vivo and short-term in vivo experiments. In both conditions, the Ang II-induced activation of procolalpha(2)(I) in renal cortex was blocked by an endothelin receptor antagonist. CONCLUSIONS: During chronic inhibition of NO, the collagen I gene becomes activated, leading to the development of renal vascular fibrosis. Ang II is a major player in this fibrogenic process, and its effect on collagen I gene is independent of systemic hemodynamics and is at least partly mediated by the profibrogenic action of endothelin.

Role of angiotensin in the renal vasoconstriction observed during the development of genetic hypertension.

Studies have examined renal function to determine the role of the kidney in the pathogenesis and maintenance phases of hypertension in the Okamoto-Aoki strain of spontaneously hypertensive rat (SHR). As compared to age-matched Wistar-Kyoto rats (WKY), 4- to 6-week old SHR are moderately hypertensive and have a reduced glomerular filtration rate (GFR) and renal blood flow (RBF), and an increased renal vascular resistance. Cross-breeding studies indicate the reduction in RBF and GFR in young SHR is genetically linked to the hypertension and thus may be of primary pathogenetic importance. The combination of an elevated vascular resistance and reduced RBF and GFR in young SHR implicates increased activity of a vasoconstrictor system(s), decreased activity of a vasodilator system(s), or both. Observations from several laboratories support the notion that endogenous angiotensin II contributes to the renal vasoconstriction in young SHR during the developmental phase of hypertension. Acute and chronic inhibition of angiotensin converting enzyme reduce arterial pressure, reduce renal vascular resistance and increase renal blood flow in young and adult SHR. Renal vascular tone in SHR is more dependent on angiotensin converting enzyme activity than that in WKY. The ability of angiotensin converting enzyme inhibitors to produce renal vasodilation may be responsible, at least in part, for its antihypertensive effects. Other studies indicate that renal vascular reactivity to angiotensin II is exaggerated in young SHR. The strain differences in renal reactivity to angiotensin II can be abolished by cyclooxygenase inhibition with indomethacin, indicating that endogenous prostanoids counteract some of the constrictor action of angiotensin II, with more pronounced buffering activity in WKY.(ABSTRACT TRUNCATED AT 250 WORDS)

[Role of nitric oxide in the regulation of arterial pressure and renal function]. / Rôle du monoxyde d'azote dans la régulation de la pression artérielle et de la fonction rénale.

Nitric oxide (NO) is produced by three isoforms of NO synthase which catalyze the oxidation of L-arginine. Endothelial and neuronal NO synthases are constitutive and activated by an increase of intracellular calcium concentration. Activity of the inducible NO synthase is implied in inflammatory processes and does not depend on intracellular calcium. In the vessels, NO induces an active vasodilatory tone. Inhibition of NO synthases by L-arginine analogs results in a long-lasting pressor effect with renal damage, which demonstrates the role of the NO in the control of blood pressure and renal function. A defect of NO synthesis by endothelial or renal cells could be involved in the pathogenesis of salt-sensitive hypertension whereas, in other forms of hypertension, vascular NO would have a compensatory role. In the kidney, NO regulates glomerular filtration by vasodilating the glomerular afferent and, to a lesser extent, efferent arterioles and by increasing the ultrafiltration coefficient (Kf). NO is implied in the relationship between renal perfusion pressure and natriuresis and alters the tubulo-glomerular retrocontrol. The effects of the glomerular induction of NO synthase are under evaluation in various models of glomerulonephritis.

[Hypertension-induced fibrosis: a balance story]. / La fibrose dans l'hypertension artérielle : une histoire d'équilibre.

Cardiac remodeling is a deleterious consequence of arterial hypertension. This remodeling results in cardiac transcriptomic changes induced by mechanical and hormonal factors (angiotensin II and aldosterone are the most important). The major features of cardiac remodeling are the hypertrophy of cardiomyocytes, interstitial and perivascular fibrosis, and microvascular rarefaction. Inappropriate stimulation of the renin-angiotensin-aldosterone system (RAAS) participates to the development of heart failure. The respective roles of angiotensin II and aldosterone in cardiac remodeling are poorly understood. The development of fibrosis in the heart depends of a balance between profibrotic (TGFß, CTGF, inflammation) and antifibrotic (BNP, ANP, BMP4 and BMP7) factors. The profibrotic and proinflammatory effects of angiotensin II and aldosterone are very well demonstrated; however, their actions on antifibrotic factors expression are unknown. In order to explore this, we used RenTgKC mice overexpressing renin into the liver, leading to an increased plasma angiotensin II and thus induction of severe hypertension, and AS mice overexpressing aldosterone synthase (AS) in cardiomyocytes which have a doubled intracardiac aldosterone concentration. Male AS mice have a dysfunction of the coronary arteries relaxation without structural and functional changes of the myocardium. Mice derived from a crossing between the RenTgKC and AS strains were used in this work. It is shown that angiotensin II induces the expression of BNP and BMPs which ultimately slows the progression of myocardial fibrosis, and that aldosterone inhibits the expression of these factors and thus worsens the fibrosis.

The role of prostaglandin and thromboxane synthesis by the glomeruli in the development of acute renal failure.

Six hours after glycerol (G) injection in normal rats (NR), creatinine clearance (Ccr) decreased while urinary TXB2 (TXA2), 6-keto-PGF1 alpha (PGI2) and PGE2 significantly increased. The administration of OKY-046, a selective TXA-synthase inhibitor in glycerol-treated rats (GTR), significantly prevented the decrease in Ccr (indicating a partial protection against the development of acute renal failure) (ARF) and the increase in urinary TXA2 excretion, while it did not significantly alter urinary prostaglandin (PG) excretion. However, although TXB2 synthesis by the isolated glomeruli (IG) obtained from rats sacrificed 2 and 6 h after G injection was significantly enhanced, PGE2 and 6-keto-PGF1 alpha (6kPGF1 alpha) synthesis was augmented only by the IG obtained from rats killed 6 h after G administration. TXB2 and 6kPGF1 alpha synthesis by the IG obtained from rats killed 24 h after G injection returned to normal levels, while PGE2 synthesis continued to be elevated. Thus the enhanced release of PGE2 and 6kPGF1 alpha observed in intact animals in the early phase of ARF must be of medullary origin, while the augmented release of TXB2 (TXA2) by the IG must be responsible for the afferent arteriolar contraction during the early phase of this syndrome.

Endothelin and renal vascular fibrosis: of mice and men.

The present review focuses on recent data regarding the role of endothelin as a mediator of renal vascular fibrosis. Following a brief description of the endothelin system, the question of whether endothelin is involved in hypertensive mechanisms is examined in experimental, genetic and transgenic animal models. Evidence is provided that implicates endothelin as an important factor of the development of tissue fibrosis and end-organ damage associated with hypertension, with particular emphasis on renal vascular fibrosis. Data indicating that endothelin interacts with other vasoconstrictor systems, such as angiotensin II, are also considered. Finally, results from preliminary clinical studies using endothelin receptor antagonists to treat cardiac and renal pathologies are briefly discussed.

Impaired ability of prostaglandins to buffer renal vasoconstriction in genetically hypertensive rats.

The purpose of this study was to gain insight into the mechanism(s) responsible for the exaggerated angiotensin II (ANG II)-induced renal vasoconstriction during the development of hypertension. In previous studies we observed that ANG II produces a twofold larger decrease in renal blood flow (RBF) in spontaneously hypertensive (SHR) compared with Wistar-Kyoto (WKY) rats before but not after cyclooxygenase inhibition. We suggested that this strain difference could be attributed to differences in renal prostaglandin (PG) levels and/or action. To evaluate these possibilities, measurements of RBF were made in 6-wk-old, anesthetized SHR and WKY pretreated with indomethacin. ANG II was injected intrarenally before and during continuous intrarenal infusion of a low dose of PGE2, viprostol (PGE2 analogue), PGI2, iloprost (PGI2 analogue), and bradykinin. In the control period ANG II reduced RBF by 50% in both strains. Infusion of PGs reduced the vasoconstrictor effect of ANG II in WKY, but had no effect in SHR. In contrast, infusion of bradykinin blunted the ANG II-induced vasoconstriction to a similar degree in both WKY and SHR. To investigate whether this lack of protection in SHR is due to strain differences in the number and/or affinity of renal receptors of PGs, radiolabeled ligand binding studies for PGE2 and PGI2 receptors were undertaken in glomeruli isolated from young WKY and SHR. Scatchard analysis revealed a single, high-affinity receptor site for PGE2 that was similar in both strains of rats. Both strains also exhibited a single, high-affinity PGI2 receptor site. No differences were observed in the PGE2 or PGI2 receptor number between WKY and SHR.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin and thromboxane in genetically hypertensive rats: renal blood flow and receptor studies.

The objective of this study was to test whether angiotensin II (ANG II) and thromboxane A2 (TxA2) contribute to the increased renal vascular reactivity observed in genetic hypertension. Under control conditions, ANG II reduced renal blood flow 35% more in spontaneously hypertensive (SHR) than in Wistar-Kyoto (WKY) rats. This strain difference was abolished by inhibition of prostaglandin synthesis with indomethacin and thus may be due to a deficiency in the action of endogenous vasodilator prostaglandins. The stable TxA2-receptor agonist U 46619 produced equal reductions of renal blood flow in SHR and WKY under control conditions. However, after indomethacin, the agonist-induced vasoconstriction was 70% more in SHR than in WKY, suggesting that SHR kidneys have an increased vascular reactivity to TxA2, which is unmasked when indomethacin reduces elevated levels of endogenous TxA2. Radiolabeled ligand binding studies for ANG II and TxA2 were undertaken in glomeruli isolated from WKY and SHR at 6 and 12 wk of age. Scatchard analysis revealed a single high-affinity receptor site for ANG [dissociation constant (Kd) = 1.2 nM], which was similar in both strains and ages of rats. All groups also showed a single high-affinity TxA2 receptor site (Kd = 3.5 nM). No differences were observed in the ANG II receptor number between age-matched rats, although the density increased with age. The density of TxA2 receptors was threefold higher in young SHR and nearly twofold higher in 12-wk-old SHR than in age-matched WKY controls. These findings indicate that the exaggerated renal vascular reactivity of SHR to ANG II and TxA2 may be mediated by a shift in the balance between endogenous vasoactive prostanoids and increased density of renal TxA2 receptors.

Vascular interactions of prostaglandins with thromboxane in kidneys of rats developing hypertension.

We investigated the ability of the vasodilator prostaglandins E2 (PGE2) and I2 (PGI2) to counterbalance the vasoconstrictor action of thromboxane A2 (TxA2) in the rat renal vasculature during hypertension. In vivo measurements of renal blood flow (RBF) were made in 6-wk-old anesthetized spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats pretreated with indomethacin. The stable TxA2 agonist U-46619 was injected into the renal artery, and the magnitude and the kinetic parameters of the renal response were evaluated before and after continuous intrarenal infusion of a low dose of PGE2, viprostol (PGE2 analogue), PGI2, and iloprost (PGI2 analogue). The selected dose of vasodilator PGs did not affect arterial pressure and RBF. In the control period, the TxA2 agonist reduced RBF by 30% with a 90-s half time of recovery in both strains. Infusion of vasodilator PGs in young WKY significantly blunted the maximum vasoconstrictor effect of the TxA2 agonist and facilitated the recovery from vasoconstriction. In marked contrast, infusion of the vasodilator PGs in young SHR failed to affect the magnitude of the vasoconstrictor effect of the TxA2 agonist, although the recovery from vasoconstriction was facilitated as in WKY. On the other hand, infusion of bradykinin or dibutyryladenosine 3',5'-cyclic monophosphate (dibutyryl cAMP) blunted the TxA2-induced vasoconstriction to a similar degree in both strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin receptor sites in renal vasculature of rats developing genetic hypertension.

The purpose of the present study was to characterize angiotensin II (ANG II) receptors in renal resistance vessels of young spontaneously hypertensive rats (SHR) ANG II receptor subtypes were evaluated in biochemical and functional terms using nonpeptide ANG II antagonists of the types AT1 (Dup-753 and Dup-532) and AT2 (PD-123319 and CGP-42112). In vitro radiolabeled ligand binding studies were performed on preglomerular resistance vessels freshly isolated from kidneys of SHR and Wistar-Kyoto (WKY) rats. The method of isolation and purification of renal microvessels was based on iron oxide infusion into the kidneys and separation of the vessels with the aid of a magnetic field followed by successive passages through various sized sieves. Physiological receptor expression was evaluated in vivo by measuring renal blood flow responses to ANG II injected alone and in a mixture with a receptor antagonist into the renal artery of indomethacin-treated rats. Our results indicate the existence of at least two functional (vasoconstriction mediating) subtypes of ANG II receptors sites in the renal microcirculation. Eighth percent of the ANG II receptor sites displayed high affinity to Dup-753 and Dup-532 and low affinity to PD-123319 and CGP-42112, whereas the remaining 20% of sites showed low affinity to Dup-753 and Dup-532 and CGP-42112 and intermediate affinity to PD-123319. In addition, the renal vasculature of young SHR and WKY displays similar ANG II receptor characteristics and identical blood flow responses to ANG II and to mixtures of ANG II and its antagonists.

Renal vascular reactivity to vasodilator prostaglandins in genetically hypertensive rats.

The objective of this study was to test the hypothesis that the vasodilator prostaglandins E2 (PGE2) and PGI2) participate in the mechanisms involved in the increased renal vascular reactivity (RVR) observed in genetic hypertension. Studies were performed on anesthetized young and adult spontaneously hypertensive (SHR) and Wistar-Kyoto rats (WKY). Renal blood flow (RBF) was measured during bolus injections into the renal artery of different doses of viprostol and iloprost (stable receptor agonists of PGE2 and PGI2, respectively) before and during inhibition of prostaglandin synthesis by indomethacin. Under control conditions, PGE2 increased RBF equally in young SHR and WKY. However, after cyclooxygenase inhibition the PGE2-induced increase in RBF was larger in young SHR than in WKY. Adult SHR displayed reduced reactivity to PGE2 relative to age-matched WKY under control conditions. This strain difference was abolished after indomethacin administration. PGI2 increased RBF slightly in young rats before and after indomethacin administration. In contrast, both strains of older animals displayed significant increases in RBF in response to PGI2 injections. Indomethacin administration enhanced this PGI2-induced relaxation in adult SHR but not WKY. We propose that the action of vasodilator PGs in the renal vasculature of rats developing hypertension may be limited by low density of their renal receptors and/or the opposing action of vasoconstrictor PGs. As age advances, PGI2 seems to be activated, possibly as part of a regulatory response to counterbalance the increased renal vascular resistance following the establishment of the disease.

Prostaglandin interactions with angiotensin, norepinephrine, and thromboxane in rat renal vasculature.

The objective of this study was to investigate the ability of the vasodilator prostaglandins E2 (PGE2) and I2 (PGI2) to interact with the vasoconstrictor action of angiotensin II (ANG II), norepinephrine (NE), and thromboxane A2 (TxA2) in the renal vasculature. In 12-wk-old anesthetized Munich-Wistar rats pretreated with indomethacin, renal blood flow (RBF) was measured during bolus injection of ANG II, NE, U-46619 (TxA2 agonist), PGE2, viprostol (PGE2 agonist), PGI2 or iloprost (PGI2 agonist) into the renal artery. Agents were injected separately and in a mixture of one constrictor with one dilator. ANG II, NE, and U-46619 induced large decreases in RBF, whereas PGs and their analogues produced slight, but significant, vasodilatation. To evaluate possible interactions in the vasomotor mechanisms between the dilators and the constrictors, curves of transient responses of separate injections were added (one constrictor plus one dilator) to create a predicted response of a mixture. NE exhibited additive effects with all PGs, as evidenced by the similarity of measured and predicted responses. In contrast, the TxA2 agonist interacted in a nonlinear fashion with all PGs; the measured maximum vasoconstriction was less than that predicted, and all kinetic parameters for the measured response were shorter than those predicted. The measured response to mixtures of ANG II and all PGs had a faster recovery than that predicted. We propose that the similarity between measured and predicted responses is due to independent actions of these agents via distinct mechanisms. In contrast, nonadditive responses suggest that the mechanisms mediating vasomotor effects of these agents interact in some cellular event.

Exaggerated renal vascular reactivity to angiotensin and thromboxane in young genetically hypertensive rats.

The objective of this study was to test the hypothesis that angiotensin II and thromboxane A2 (TxA2) contribute to the elevated renal vascular resistance observed during the development of genetic hypertension. In 6-wk-old anesthetized spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats, renal blood flow (electromagnetic flowmetry) and carotid arterial pressure were measured during bolus injections of different doses of angiotensin II and U46619 (stable receptor agonist of TxA2) into the renal artery before and during inhibition of prostaglandin synthesis by indomethacin. In all cases, arterial pressure remained unchanged at the pre-injection levels. Under control conditions, angiotensin II reduced renal blood flow in SHR almost twice as much as in WKY. This strain difference was abolished by inhibition of prostaglandin synthesis, suggesting that a deficiency in the action of endogenous vasodilator prostaglandins is responsible for the enhanced response to angiotensin II in SHR. Under control conditions, the TxA2-receptor agonist produced similar reductions of renal blood flow in SHR and WKY. However, after indomethacin, the agonist-induced vasoconstriction was twice as large in SHR as in WKY, suggesting that SHR kidneys have an increased vascular reactivity to TxA2, which is unmasked when indomethacin reduces elevated levels of endogenous TxA2. These findings indicate important strain differences between young SHR and WKY in the renal vascular response to angiotensin II and TxA2 that may contribute to the renal vasoconstriction observed during the development of genetic hypertension.