LIM-class homeobox gene Lim1, a novel oncogene in human renal cell carcinoma.

Human clear cell renal cell carcinoma (CCC) remains resistant to therapies. The transcription factor LIM-class homeobox gene Lim1 is required for normal organogenesis, including nephrogenesis, by regulating cell movements, differentiation and growth. Its expression is controlled partly by the sonic hedgehog-Gli signaling pathway, which we have recently shown to be reactivated in human CCC. So far, no study has assessed whether Lim1 may be associated with tumorigenesis. Using a panel of human CCC cell lines expressing or not the von Hippel-Lindau tumor suppressor gene and 44 tumor/normal tissues pairs, we found that Lim1 is constitutively and exclusively reexpressed in tumors. Through Lim1 silencing or overexpressing, we show that Lim1 is a growth and survival factor in human CCC, at least through the activation of oncogenic pathways including the phosphoinositide kinase-3/Akt and nuclear factor-kappaB pathways. More importantly, in nude mice bearing human CCC tumors, Lim1 silencing abolished tumor growth through the same mechanism as in vitro. In Lim1-depleted cells and tumors, cell movements were substantially impaired because of the inhibition of expression of various proteins involved in metastatic spread, such as paxillin or tenascin-C. These findings establish that the developmental marker Lim1 acts as an oncogene in cancer cells and targeting Lim1 may constitute an innovative therapeutic intervention in human CCC.

Peritoneal dialysis in children: consider the membrane for optimal prescription.

The peritoneal dialysis prescription was, for a long time, based on clinical experience and very empirical, especially for patients on continuous ambulatory peritoneal dialysis (CAPD). Better comprehension of the peritoneal membrane as a dynamic dialysis surface allows an individualized prescription, especially for children on automated peritoneal dialysis (APD). Fill volume prescription should be scaled for body surface area (mL/m(2)) and not in a too low amount to avoid a hyperpermeable exchange. Fill volume enhancement should be done under clinical control and is best secured by intraperitoneal pressure measurement (IPP; cm H2O). A peak fill volume of 1400-1500 mL/m(2) could be prescribed both in terms of tolerance and of efficiency. The dwell times should be determined individually with respect to two opposite parameters namely: short dwell times which provide adequate small solute clearance and maintain ultrafiltration capacity and long dwell times which enhance phosphate clearance but can contribute to dialysate reabsorption. The new peritoneal dialysis fluids which are free of GPD's, have neutral pH and are not exclusively lactate buffered, appear as the best choice in the context of peritoneal exchange membrane recruitment and of peritoneal vascular hyperperfusion preservation.

Mild acute renal failure potentiates metformin accumulation in the diabetic rat kidney without further impairment of renal function.

OBJECTIVES: To analyze, in acute renal failure (ARF) in diabetic rats, how moderate functional ARF would modify metformin (MET) pharmacokinetics and if plasma and renal tissue MET accumulation could aggravate renal insufficiency and/or elicit plasma lactate accumulation. METHODS: Streptozotocin-induced diabetic rats were allocated to four groups: control, MET, ARF, ARF-MET (6-7 rats per group). MET (100 mg/kg/day) was given per os for two weeks before ARF was induced by drinking restriction and enalapril treatment. The effects of MET and/or ARF were examined in vivo on renal function in conscious rats (metabolic cages) and ex vivo on renal vascular reactivity (isolated kidney). RESULTS: MET treatment (plasma level: 5.3 +/- 1.4 microg/ml, mean+/-SEM), resulted in biguanide accumulation in cortex and medulla (53 +/- 17 and 80 +/- 40 microg/g respectively). MET was devoid of any effect on creatinine clearance, mean blood pressure or renal vascular resistance, but moderately increased plasma lactate (3.8 +/- 0.5 vs 3.2 +/- 0.2 mM, P<0.05) and decreased angiotensin II-induced renal vasoconstriction. ARF, although mild, decreased renal MET clearance (0.29 +/- 0.05 vs 1.01 +/- 0.31 ml/min/100 g, P<0.05) and increased plasma and renal tissue MET levels (x 2-4). MET however did not worsen the fall in glomerular filtration rate, nor modify renal vascular reactivity. ARF did not change the MET-elicited moderate increase in plasma lactate. CONCLUSION: Despite the increase in MET plasma and renal tissue levels subsequent to moderate ARF, no harmful metabolic effect on plasma lactate and no further impairment of renal function was observed in MET-treated diabetic rats subjected to ARF.

Renal vascular reactivity to vasopressin in rats with diabetes mellitus.

We evaluated how renal vascular reactivity to vasopressin changes when nitric oxide (NO) synthesis varies, as has been reported to occur in the course of insulin-dependent diabetes mellitus. Renal vasoconstrictor responses to vasopressin were obtained in young and older Sprague-Dawley control rats (3 and 10 months old) and in age-matched diabetic rats that had been treated with streptozotocin (60 mg/kg i.v.) at the age of 2 months. In young rats, vasopressin (3-1000 ng/kg/min i.v.) induced in vivo a dose-dependent decrease in renal blood flow, which was diminished in streptozotocin diabetic rats (P<0.05). Similarly, in in vitro perfused kidneys, the concentration-response curve for vasopressin (0.03-10 nM) was shifted 3-fold to the right in kidneys isolated from young diabetic rats (P<0.05). This shift was abolished in the presence of an inhibitor of nitric oxide synthesis, N(G)-nitro-L-arginine (100 microM), in the perfusate. In 10-month-old rats, the in vivo renal vasoconstrictor dose-response curve to vasopressin was shifted 10-fold to the left as compared to that for young rats (P<0.001). This shift was similar in both control and diabetic rats. In conclusion, the present study documented the existence of hyporesponsiveness to vasopressin in the early stage of diabetes, possibly related to nitric oxide overproduction. In contrast, renal vascular hyperreactivity to vasopressin occurs with aging, whether the rats are diabetic or not.

Involvement of brain mineralocorticoid receptor in salt-enhanced hypertension in spontaneously hypertensive rats.

We recently showed that brain mineralocorticoid receptors (MRs) are involved in blood pressure and kidney function control in normotensive Wistar rats. We now assessed the involvement of brain MRs in spontaneously hypertensive rats (SHR), in which the presence of adrenocorticoids has been shown to be required for the development of hypertension. The effect of a single intracerebroventricular (ICV) injection of an MR antagonist (RU28318) on systolic blood pressure (SBP) and renal function was examined in conscious adult SHR and Wistar-Kyoto rats (WKY) maintained on a standard-sodium diet (0.4% Na(+)). In WKY, a long-lasting decrease in SBP was caused by the ICV injection of 10 ng RU28318 as previously reported in Wistar rats, associated with increased urinary excretion of water and electrolytes. In SHR maintained on the standard diet, the ICV injection of RU28318 (10 or 100 ng) had no effect on cardiovascular and renal functions. However, the ICV injection of 10 ng RU28318 in SHR after 3 weeks of high sodium intake (8% Na(+)) caused a long-lasting decrease in SBP. The effect was present at 8 hours (DeltaSBP 34+/-2 mm Hg), persisted at 24 hours (DeltaSBP 29+/-1 mm Hg), and disappeared at 48 hours after the injection. The hypotension was not associated with changes in heart rate, urinary excretion of water and electrolytes, and plasma renin activity, whereas renal denervation did not affect the decrease in SBP. A more pronounced decrease in SBP (49+/-3 mm Hg at 8 hours) was observed with 100 ng RU28318. This dose of the antagonist was without effect after subcutaneous administration. Thus, brain MRs appear to participate in the maintenance of hypertension in conscious adult SHR sensitized by sodium loading.

[Effect of a non-antihypertensive dose of ramipril on the plasma and tissue renin-angiotensin system in 27 TGR (mRen2) rats]. / Effets d'une dose non antihypertensive de ramipril sur les systèmes rénine-angiotensine plasmatique et tissulaire chez le rat TGR (mRen-2) 27.

It is admitted that low dose of angiotensin converting enzyme (ACE) inhibitors allows the regression of left ventricular hypertrophy (HVG) in experimental models where plasma renin activity (PRA) is high. The use of low dose of ramipril, an ACE inhibitor, make it possible to explore the place of cardiac renin-angiotensin system (RAS) in the regression of HVG independently of blood pressure (BP). Twenty rats TGR (mRen2) 27, heterozygous male, 10 weeks old were treated by daily oral gavage during 6 weeks by 10 micrograms/kg/jour ramipril or distilled water and compared to 10 normotensive Sprague Dawley (SD) rats. BP was measured. After the period of treatment, plasma, left kidney and the ventricles were removed. On each tissue samples and plasma, angiotensinogen (Aogen), the renin activity, angiotensins I (Ang I) and II (Ang II) were determined by radioimmuno assay and the activity of ACE was measured by fluorimetry. BP does not differ between treated and untreated groups during 6 weeks of treatment but is significantly higher compared to SD rats. PRA of untreated rats is high (36 +/- 5 ng Ang I/mL/h). However, treatment did not make it possible to decrease HVG. In plasma and kidney treatment's effect on SRA is confirmed by the increase in renin activity (plasma: 63 +/- 9 vs 36 +/- 5 ng Ang I/mL/h; kidney: 127 +/- 11 vs 92 +/- 7 micrograms Ang I/g/h) which is accompanied by an increase of Ang I rates (plasma: 297 +/- 31 vs 15 +/- 10 fmol/mL; kidney: 241 +/- 37 vs 160 +/- 12 fmol/g) and of the reduction in Aogen. An inhibition of ACE is perceptible with low dose of ramipril in heart (left ventricle: 1.7 +/- 0.1 vs 2.5 +/- 0.3 nmol HisLeu/min/mg protein), but it does not appear significant modifications of the other elements of the RAS in this tissue. The Ang II cardiac rates are probably not solely defined by cardiac ACE activity, other ways of synthesis being described. The absence of regression of the HVG in TGR (mRen2) 27 rat with low dose of ramipril could be related to the absence of effect on cardiac Ang II rates. In addition, the relation between high PRA rates and the effectiveness of low dose of ACE inhibitor in the HVG are not confirmed.

High concentrations of oxytocin cause vasoconstriction by activating vasopressin V1A receptors in the isolated perfused rat kidney.

The aim of this study was to evaluate the renal vascular effects of oxytocin in Sprague-Dawley rats and in Brattleboro heterozygous or homozygous rats, the latter being genetically deficient in vasopressin synthesis. Studies were performed in vitro, in the isolated kidney perfused in an open circuit with a Tyrode's solution. Oxytocin induced a concentration-dependent renal vasoconstriction in Sprague-Dawley rats, at rather high concentrations (EC50=170+/-39 nM, mean +/- SEM, n=6) with a maximum response amounting to 44% of that elicited by vasopressin (increase in renal vascular resistance: 11.5+/-0.9 mmHg min ml(-1) vs. 26.2+/-2.2 mmHg min ml(-1)). Oxytocin-evoked renal vasoconstriction was abolished by SR 49059, a selective vasopressin V1A receptor antagonist (10 nM), but not by d(CH2)5[Tyr(Me)2,Thr4,Orn8,Tyr-(NH2)9] vasotocin, an oxytocin receptor antagonist (10 nM). In the presence of SR 49059, oxytocin did not induce renal vasorelaxation. Oxytocin induced renal vasoconstriction in Brattleboro homozygotes and heterozygotes (EC50=59+/-12 nM and 262+/-110 nM; Emax=7.8+/-1.1 mmHg min ml(-1) and 6.9+/-0.4 mmHg min ml(-1), n=5 respectively) with characteristics similar as observed in Sprague-Dawley rats concerning partial agonist activity, low potency and antagonism by SR 49059. Responsiveness to vasopressin did not differ in Brattleboro homozygotes and heterozygotes (EC50 approximately 0.25 nM) and was similar as we reported in Sprague-Dawley rats. These findings indicate that high concentrations of oxytocin induce renal vasoconstriction in the rat by activating vasopressin V1A receptors. The low agonist activity makes it unlikely that oxytocin can substitute functionally for vasopressin at the renal vascular V1A receptor in Brattleboro homozygous rats which are deficient in endogenous vasopressin.

Effects of icatibant on the ramipril-induced decreased in renal lithium clearance in the rat.

The interaction between an inhibitor of angiotensin I converting enzyme (ramipril) and renal lithium handling was analysed in conscious, normotensive Wistar rats in the absence or the presence of a specific bradykinin B2 receptor antagonist, icatibant. The rats were treated for 5 days with ramipril (1 mg/kg/day p.o.) or its vehicle, alone or together with icatibant (0.1 mg/kg/day, s.c. infusion). Lithium chloride (8.3 mg/kg i.p.) was given as a single dose on day 5. Systolic blood pressure and heart rate were measured by tail plethysmography on day 3 (3, 9 and 15 h after ramipril administration) and renal function on day 4 (0-6 and 6-24 h urine sampling) and day 5 (0-6 h urine sampling). In another group of rats, 24 h sodium excretion was assessed during the first 4 days of ramipril treatment. Ramipril decreased renal lithium clearance (90+/-8 vs. 142+/-10 microl/min/100 g, P<0.001, n=24) and increased the fractional lithium reabsorption (74.3+/-1.9 vs. 66.7+/-1.7%, P<0.05) and plasma lithium concentration (0.108+/-0.006 vs. 0.085+/-0.004 mM, P<0.01). Alteration of renal lithium handling by ramipril was associated with a decrease in systolic blood pressure (-15% 3 h after ramipril administration) and sodium excretion (0-6 h after ramipril). The 24-h sodium excretion, however, tended to increase. Icatibant had no effect per se on renal function but attenuated the ramipril-induced decrease in renal lithium clearance (118+/-16 vs. 90+/-8 microl/min/100 g, n=12 and 24 respectively, P<0.05 one-tailed test) and systolic blood pressure. These results suggest that endogenous bradykinin contributes to the ramipril-associated alteration in renal lithium handling. Bradykinin B2 receptor-mediated vasodilation seems to be involved.

Signal transduction pathways involved in kinin B(2) receptor-mediated vasodilation in the rat isolated perfused kidney.

The signal transduction pathways involved in kinin B(2) receptor-related vasodilation were investigated in rat isolated perfused kidneys. During prostaglandin F(2alpha) or KCl-induced constriction, the vasodilator response to a selective B(2) receptor agonist, Tyr(Me)(8)bradykinin (Tyr(Me)(8)BK), was assessed. Tyr(Me)(8)BK produced a concentration- and endothelium-dependent relaxation that was decreased by about 30 - 40% after inhibition of nitric oxide (NO) synthase by N(G)-nitro-L-arginine (L-NOARG) or of cyclo-oxygenase by indomethacin; a greater decrease (about 40 - 50%) was observed after concomitant inhibition of the two pathways. High extracellular K(+) diminished Tyr(Me)(8)BK-induced relaxation by about 75% suggesting a major contribution of endothelium-derived hyperpolarization. The residual response was almost completely suppressed by NO synthase and cyclo-oxygenase inhibition. The K(+) channel inhibitors, tetrabutylammonium (non-specific) and charybdotoxin (specific for Ca(2+)-activated K(+) channel), suppressed Tyr(Me)(8)BK-induced relaxation resistant to L-NOARG and indomethacin. Inhibition of cytochrome P450 (clotrimazole or 7-ethoxyresorufin) decreased the NO/prostanoids-independent relaxation to Tyr(Me)(8)BK by more than 60%, while inhibition of the cannabinoid CB(1) receptor (SR 141716A) had only a moderate effect. Acetylcholine induced a concentration-dependent relaxation with characteristics nearly similar to the response to Tyr(Me)(8)BK. In contrast, the relaxation elicited by sodium nitroprusside was potentiated in the absence of NO (L-NOARG or removal of endothelium) but remained unchanged otherwise. These results indicate that the activation of kinin B(2) receptors in the rat isolated kidney elicits an endothelium-dependent vasorelaxation, mainly dependent on the activation of charybdotoxin-sensitive Ca(2+)-activated K(+) channels. In addition, cytochrome P450 derivatives appear to be involved.

Paradoxical actions of exogenous and endogenous parathyroid hormone-related protein on renal vascular smooth muscle cell proliferation: reversion in the SHR model of genetic hypertension.

In previous studies, added parathyroid hormone-related protein (PTHrP) inhibits whereas transfected PTHrP stimulates the proliferation of A10 aortic smooth muscle cells by nuclear translocation of the peptide. In the present studies, we asked whether these paradoxical trophic actions of PTHrP occur in smooth muscle cells (SMC) cultured from small intrarenal arteries of, and whether they are altered in, 12-wk-old spontaneously hypertensive rats (SHR) as compared to normotensive Wistar-Kyoto (WKY) rats. SHR cells grew faster than WKY cells. PTHrP transcript was increased in SHR-derived cells whereas PTH1 receptor (PTH1R) transcripts were similar in both cell lines. In both strains of cells, stable transfection with human PTHrP(1-139) cDNA did not further induce proliferation, suggesting maximal effect of endogenous PTHrP in wild cells. In contrast, transfection with antisense hPTHrP(1-139) cDNA, which abolished PTHrP mRNA, decreased WKY but increased SHR cell proliferation. Added PTHrP(1-36) (1-100 pM) decreased WKY and increased SHR cell proliferation. Additional studies indicated that the preferential coupling of PTH1-R to G-protein Gi was responsible for the proliferative effect of exogenous PTHrP in SHR cells. Moreover, PTHrP was detected in the nucleolus of a fraction of WKY and SHR renal SMC, in vitro as well as in situ, suggesting that the nucleolar translocation of PTHrP might be involved in the proliferative effects of endogenous PTHrP. In renovascular SMC, added PTHrP is antimitogenic, whereas endogenously produced PTHrP is mitogenic. These paradoxical effects of PTHrP on renovascular SMC proliferation appear to be reversed in the SHR model of genetic hypertension. A new concept emerges from these results, according to which a single molecule may have opposite effects on VSMC proliferation under physiological and pathophysiological conditions.

Inhibitory effect of reactive oxygen species on angiotensin I-converting enzyme (kininase II).

1. Somatic angiotensin I-converting enzyme (ACE) is a protein that contains two similar domains (N- and C-terminal), each possessing an active site. We have examined the effects of a generator of hydroxyl radicals (g*OH: 2,2'-azo-bis(2-amidinopropane)) and hydrogen peroxide (H2O2) on ACE using an in vitro approach. 2. The generator of hydroxyl radicals inactivated ACE in a time (2-6 h)- and concentration (0.3-3 mmol/L)-dependent manner at 37 degrees C. When ACE was coincubated for 4 h with g*OH (3 mmol/L), its activity decreased by 70%. Addition of dimethylthiourea or mannitol + methionine, two *OH scavengers, resulted in a significant protection of ACE activity. Mercaptoethanol and dithiotreitol, two thiol-reducing agents, also efficiently protected ACE activity. 3. The hydrolysis of two natural and domain-specific substrates was explored. The hydrolysis of angiotensin I, preferentially cleaved by the C-domain, was significantly inhibited (57-58%) after 4 h exposure to g*OH (0.3-1 mmol/L). Under the same conditions of exposure, the hydrolysis of N-acetyl-Ser-Asp-Lys-Pro, a specific substrate for the N-domain, was only slightly inhibited by 1 mmol/L g*OH. 4. Hydrogen peroxide, another source of *OH, was used. After exposure to H2O2 (3 mmol/L; 4 h), an 89% decrease in ACE activity was observed. Pretreatment with the iron chelator deferoxamine (1 mmol/L) attenuated H2O2-mediated ACE inactivation, demonstrating that the effect of H2O2 was partly due to its conversion into *OH (Fenton reaction). 5. In summary, our findings demonstrate that g*OH and H2O2 inhibit ACE activity and suggest a preferential action of g*OH on the C-domain of the enzyme.

Vascular catabolism of bradykinin in the isolated perfused rat kidney.

Kinins in the circulation are rapidly metabolized by several different peptidases. The purpose of this study was to evaluate the contribution of membrane-bound peptidases to kinin metabolism in the renal circulation. Experiments were performed in vitro, in isolated rat kidneys perfused at a constant flow rate (8 ml/min) with Tyrode's solution. The effects of peptidase inhibitors were evaluated on the functional vasodilator response caused by bradykinin (30 nM) or [Tyr(Me)(8)]bradykinin (10 nM) via activation of bradykinin B2 receptors in kidneys precontracted with prostaglandin F2alpha. Angiotensin converting enzyme inhibitors, enalaprilat (3 microM), ramiprilat (1 microM) or lisinopril (1 microM), increased the bradykinin-induced renal vasodilation by 40% or more. Inhibitors of neutral endopeptidase (thiorphan or phosphoramidon, 10 microM), basic carboxypeptidase (DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid or MGTPA, 10 microM) and aminopeptidase P (apstatin, 20 microM) however did not enhance the renal vasodilator response elicited by kinins, whatever tested alone or in the presence of lisinopril. These findings indicate that angiotensin converting enzyme is the major peptidase whose inhibition potentiates the renal bradykinin B2 receptor mediated vasodilator response of kinins. The relative contribution in this potentiation of inhibition of kinin inactivation and of cross-talk of angiotensin converting enzyme with bradykinin B2 receptor remains however to be clarified.

Nitric oxide, but not vasopressin V2 receptor-mediated vasodilation, modulates vasopressin-induced renal vasoconstriction in rats.

The renal vascular response to vasopressin and its modulation were evaluated in vivo by infusing the peptide directly into the renal artery of anaesthetized rats. The intra-renal artery (i.r.a) infusion of vasopressin induced a dose-dependent decrease in renal blood flow. Vasoconstriction was obvious at a dose of 3 ng/kg per min and reached a maximum at 100 ng/kg per min. The dose required for a half-maximal response (ED50) was 24+/-4 ng/kg per min (mean+/-SEM, n=8), corresponding to an estimated concentration in renal arterial blood required for a half-maximal response (EC50) of 1.9+/-0.6 nM. Thiobutabarbitone anaesthesia markedly increased plasma vasopressin concentration. This increase was prevented partially by hypotonic hydration of the rats without any change in the renal vascular response to exogenous vasopressin. Vasopressin-induced vasoconstriction dose/response curves were similar in homozygous and heterozygous Brattleboro rats. Infusion of desmopressin (1-1000 ng/kg per min, i.r.a.), a vasopressin V2 receptor-selective agonist, failed to induce renal vasodilation or vasoconstriction. In the presence of SR 49059 (1 mg/kg i.v.), a vasopressin V1A receptor antagonist that completely abolished the vasopressin-induced renal vasoconstriction, desmopressin again failed to induce vasodilation. Inhibition of nitric oxide synthase by N(omega)-nitro-L-arginine (L-NNA, 100 microg/kg for 10 min and 7.5 microg/kg per min, i.r.a.) enhanced vasopressin-induced renal vasoconstriction (EC50 0.6+/-0.1 nM, P<0.05). In contrast, cyclooxygenase blockade by indomethacin (5 mg/kg, i.v.) neither modified the vasopressin-induced decrease in renal blood flow nor altered the potentiation of vasoconstriction by L-NNA. These results show that the constrictor response of the rat renal vascular bed in vivo is observed only with high local concentrations of vasopressin. This hyporeactivity in vivo was not explained by an anaesthesia-elicited increase in endogenous vasopressin, nor by a modulatory effect linked to V2 receptor activation or prostanoid release. In contrast, NO release contributed to the attenuation of vasopressin-induced renal vasoconstriction.

Vasopressin does not effect hypertension caused by long-term nitric oxide inhibition.

Nitric oxide attenuates both vasopressin-induced vasoconstriction and vasopressin release. We tested whether hypertension and renal dysfunction elicited by chronic inhibition of nitric oxide (NO) synthesis using N(G)-nitro-L-arginine (L-NNA) could be mediated in part by vasopressin V(1A) receptors. Male rats were treated orally for 6 weeks with L-NNA (15 mg/kg per day), a nonpeptide V(1A) receptor antagonist (2S)-1-[(2R,3S)-5-chloro-3-(2-chlorophenyl)-1-(3, 4-dimethoxybenzene-sulfonyl)-3-hydroxy-2, 3-dihydro-1H-indole-2-carbonyl]-pyrrolidine-2-carboxamide (SR 49059, 30 mg/kg per day), or a combination of SR 49059 and L-NNA (same doses), or they received no treatment. Both drugs were added to the food. Measurements were performed in conscious rats (urine collection in metabolic cages, tail-cuff arterial pressure) and at the end of the study in anesthetized rats (clearance measurements). L-NNA produced sustained hypertension, decreased glomerular filtration rate, and increased renal vascular resistance, plasma renin activity, and urinary albumin excretion. SR 49059 had no effect per se on these parameters and also did not attenuate the hypertension and renal dysfunction induced by L-NNA. Surprisingly, SR 49059 potentiated L-NNA-induced hypertension at the end of the 6-week treatment. However, the blood pressure response and the renal and mesenteric vasoconstriction elicited by exogenous vasopressin were attenuated in rats treated with SR 49059. L-NNA did not change plasma vasopressin concentration or 24-hour urinary vasopressin excretion. Our findings suggest that activation of vasopressin V(1A) receptors does not contribute to the hypertension and renal dysfunction induced by chronic NO synthesis inhibition. They also document unchanged plasma vasopressin concentration in NO-deficient hypertension.

Vascular kinin B(1) and B(2) receptor-mediated effects in the rat isolated perfused kidney - differential regulations.

1. Bradydykinin (BK) and analogs acting preferentially at kinin B(1) or B(2) receptors were tested on the rat isolated perfused kidney. Kidneys were perfused in an open circuit with Tyrode's solution. Kidneys preconstricted with prostaglandin F(2alpha) were used for the analysis of vasodilator responses. 2. BK induced a concentration-dependent renal relaxation (pD(2)=8.9+/-0.4); this vasodilator response was reproduced by a selective B(2) receptor agonist, Tyr(Me)(8)-BK (pD(2)=9.0+/-0.1) with a higher maximum effect (E(max)=78.9+/-6.6 and 55.8+/-4.3% of ACh-induced relaxation respectively, n=6 and 19, P<0.02). Icatibant (10 nM), a selective B(2) receptor antagonist, abolished BK-elicited relaxation. Tachyphylaxis of kinin B(2) receptors appeared when repeatedly stimulated at 10 min intervals. 3. Des-Arg(9)-BK, a selective B(1) receptor agonist, induced concentration-dependent vasoconstriction at micromolar concentration. Maximum response was enhanced in the presence of lisinopril (1 microM) and inhibited by R 715 (8 microM), a selective B(1) receptor antagonist. Des-Arg(9)-[Leu(8)]-BK behaved as an agonist. 4. A contractile response to des-Arg(9)-BK occurred after 1 of perfusion and increased with time by a factor of about three over a 3 h perfusion. This post-isolation sensitization to des-Arg(9)-BK was abolished by dexamethasone (DEX, 30 mg kg(-1) i.p., 3 h before the start of the experiment and 10 microM in perfusate) and actinomycin D (2 microM). Acute exposure to DEX (10 microM) had no effect on sensitized des-Arg(9)-BK response, in contrast to indomethacin (30 microM) that abolished it. DEX pretreatment however had no effect on BK-induced renal vasodilation. 5. Present results indicate that the main renal vascular response to BK consists of relaxation linked to the activation of kinin B(2) receptors which rapidly desensitize. Renal B(1) receptors are also present and are time-dependently sensitized during the in vitro perfusion of the rat kidneys.

Cardiovascular and renal effects of central administration of a mineralocorticoid receptor antagonist in conscious female rats.

In a previous study we showed that in normotensive male rats brain mineralocorticoid receptor blockade induced a long lasting decrease in blood pressure associated with increased urinary excretion of water and electrolytes. Here, we report the effect of intracerebroventricular injection of a mineralocorticoid receptor antagonist (RU28318; 3,3-oxo-7 propyl-17-hydroxy-androstan-4-en-17yl-propionic acid lactone) on cardiovascular and renal function in female rats. Compared with male rats, females are less sensitive to brain mineralocorticoid receptor blockade. Administration of RU28318 (10 ng, 100 ng) caused a significant decrease in systolic blood pressure (10-12.5%) only at 8 h after injection. An increased urinary excretion of water (about 160%) and electrolytes (about 175%) during the first 8 h after the injection was observed in the 100 ng RU28318 treated group. Heart rate, food intake and water consumption were not affected at either dose. In conclusion, in conscious female rats, brain mineralocorticoid receptors participate in blood pressure and renal function control.

Role of shear stress in nitric oxide-dependent modulation of renal angiotensin II vasoconstriction.

1. Renal vasoconstriction in response to angiotensin II (ANGII) is known to be modulated by nitric oxide (NO). Since shear stress stimulates the release of a variety of vasoactive compounds from endothelial cells, we studied the impact of shear stress on the haemodynamic effect of ANGII in isolated perfused kidneys of rats under control conditions and during NO synthase inhibition with L-NAME (100 microM). 2. Kidneys were perfused in the presence of cyclo-oxygenase inhibitor (10 microM indomethacin) with Tyrode's solution of relative viscosity zeta=1 (low viscosity perfusate, LVP) or, in order to augment shear stress, with Tyrode's solution containing 7% Ficoll 70 of relative viscosity zeta=2 (high viscosity perfusate, HVP). 3. Vascular conductance was 3.5+/-0.4 fold larger in HVP as compared with LVP kidneys, associated with an augmentation of overall wall shear stress by 37+/-5%. During NO inhibition, vascular conductance was only 2.5+/-0.2 fold elevated in HVP vs LVP kidneys, demonstrating shear stress-induced vasodilatation by NO and non-NO/non-prostanoid compound(s). 4. ANGII (10 - 100 pM) constricted the vasculature in LVP kidneys, but was without effect in HVP kidneys. During NO inhibition, in contrast, ANGII vasoconstriction was potentiated in HVP as compared with LVP kidneys. 5. The potentiation of ANGII vasoconstriction during NO inhibition has been shown to be mediated by endothelium-derived P450 metabolites and to be sensitive to AT2 receptor blockade in our earlier studies. Accordingly, in HVP kidneys, increasing concentrations of the AT2 receptor antagonist PD123319 (5 and 500 nM) gradually abolished the potentiation of ANGII vasoconstriction during NO inhibition, but did not affect vasoconstriction in response to ANGII in LVP kidneys. 6. Our results demonstrate, that augmentation of shear stress by increasing perfusate viscosity induces vasodilatation in the rat kidney, which is partially mediated by NO. Elevated levels of shear stress attenuate renal ANGII vasoconstriction through enhanced NO production and are required for AT2 sensitive potentiation during NO inhibition.

Brain mineralocorticoid receptor control of blood pressure and kidney function in normotensive rats.

Brain mineralocorticoid receptors appear to contribute to mineralocorticoid hypertension and may be involved in blood pressure control in normotensive rats. We examined the effect of blockade of central mineralocorticoid receptors with the use of a selective antagonist (RU28318) on cardiovascular and renal function in conscious normotensive rats. The contribution of renal innervation was evaluated in rats with bilaterally denervated kidneys. Young adult, male Wistar rats were trained for systolic blood pressure measurement by a tail sphygmographic method and accustomed to metabolic cages for collection of urine. One week before experimentation, an intracerebroventricular cannula was implanted. Systolic blood pressure was diminished 30 minutes after an intracerebroventricular dose of 10 ng of RU28318. The effect was maximal at 8 hours and was still present after 24 hours. Blood pressure returned to the basal level by 48 hours. During the period 0 to 8 hours after intracerebroventricular injection, rats treated with the antagonist showed an increase in diuresis and urinary electrolyte excretion. No significant effect on plasma renin activity, measured 8 and 30 hours after administration of RU28318, was observed. In denervated rats, the decrease in systolic blood pressure after administration of RU28318 was reduced. The difference was statistically significant compared with controls at 2 hours but not at 8 hours, and blood pressure returned to the basal value by 24 hours. The increases in diuresis and urinary electrolyte excretion induced by RU28318 were abolished in denervated rats. These results show that brain mineralocorticoid receptors are involved in blood pressure regulation and kidney function homeostasis in conscious normotensive rats. The renal nerves appear to participate in the brain mineralocorticoid receptor control of blood pressure.

[Aldosterone antagonists: new pharmacologic prospects]. / Antagonistes de l'aldostérone: nouvelles cibles pharmacologiques.

The pharmacology of the mineralocorticoid receptor antagonist spironolactone and analogues is reviewed in the light of recent discoveries regarding the primary structure of corticosteroid receptors and the different isoforms of the enzyme 11 beta-hydroxysteroid dehydrogenase. The type 2 isoform of this enzyme functions in some tissues to keep the aldosterone receptor activation specific, i.e. it allows stimulation by aldosterone while eliminating glucocorticoids such as cortisol and corticosterone. The type 2 isoform has been shown in the colon, hypothalamus, kidney, placenta and salivary gland. New clinical uses of aldosterone antagonists may be derived from these developments. Most prominent in this respect appear to be myocardial fibrosis and specific forms of hypertension with altered mineralocorticoid receptor functioning and deficiencies in the protection system of the receptor against glucocorticoids.

[Brain mineralocorticoid receptor and blood pressure control in the conscious normotensive rat]. / Intervention des récepteurs centraux aux minéralocorticoïdes dans le contrôle de la pression artérielle du rat normotendu conscient.

Brain control of arterial blood pressure in man and in animals has been studied increasingly over the last few decades. Despite our knowledge about short term regulation (chemoreceptor and baroreceptor reflexes) there is much more uncertainty about the degree of involvement of brain mechanisms in long term control of blood pressure, and in hypertension. The last decade, a role of brain mineralocorticoid receptors (MR) has been outlined in animal experiments. Stimulation of brain MR by aldosterone or related mineralocorticoids induces an increase in blood pressure and hypertension under chronic conditions. These effects of mineralocorticoid excess can be blocked by specific MR antagonists administered centrally. Stimulation of brain glucocorticoid receptors, as compared to stimulation of brain MR, has an opposite effect, i.e. decreases blood pressure. As in the typical peripheral target organs of aldosterone, in the brain, enzymatic protection of MR against glucocorticoids appears to play an important role. We showed that in conscious normotensive rats intracerebroventricular (i.c.v.) injection of a specific MR antagonist (RU28318) in a low dose (10 ng) decreases blood pressure by about 20% without affecting heart rate. A similar but smaller effect (not statistically significant) was observed in conscious female rats. Only in the male rats an increased diuresis occurred and this may have contributed to the observed hypotension. We conclude that hypertension caused by mineralocorticoid excess may depend on a concerted action of the steroid on the kidney and on the brain. The mechanism by which brain MR increases blood pressure is unknown. It is possible that increased sympathetic outflow and renal mechanisms are involved. Interference with brain MR not only affects blood pressure but it also has effect on renal function.