Transient and sustained increases in glomerular permeability following ANP infusion in rats

The present study was performed to investigate the effects of systemic atrial natriuretic peptide (ANP) infusion on the glomerular permeability to macromolecules in rats. In anesthetized Wistar rats (250-280 g), the left urether was cannulated for urine collection while simultaneously blood access was achieved. Rats were continuously infused intravenously with ANP [30 ng·kg(-1)·min(-1) (Lo-ANP; n=8) or 800 ng·kg(-1)·min(-1) (Hi-ANP; n=10)] or 0.9% NaCl (SHAM; n=16), respectively, and with polydisperse FITC-Ficoll-70/400 (molecular radius 13-90 ?) and 51Cr-EDTA for 2 h. Plasma and urine samples were taken at 5, 15, 30, 60, and 120 min of ANP infusion and analyzed by high-performance size-exclusion chromatography (HPLC) for determination of glomerular sieving coefficients (θ) for Ficoll. GFR was also assessed (51Cr-EDTA). In Hi-ANP, there was a rapid (within 5 min), but bimodal, increase in glomerular permeability. θ to high-molecular-weight Ficoll thus reached a maximum at 15 min, after which θ returned to near control at 30 min, to again increase moderately at 60 and 120 min. In Lo-ANP, there was also a rapid, reversible increase in glomerular θ, returning to near control at 30 min, followed by just a tendency of a sustained increase in permeability, but with a significant increase in "large-pore" radius. In conclusion, in Hi-ANP there was a rapid increase in glomerular permeability, with an early, partly reversible permeability peak, followed by a (moderate) sustained increase in permeability. In Lo-ANP animals, only the initial permeability peak was evident. In both Lo-ANP and Hi-ANP, the glomerular sieving pattern observed was found to mainly reflect an increase in the number and radius of large pores in the glomerular filter.     

Angiotensin II utilizes Janus kinase 2 in hypertension, but not in the physiological control of blood pressure, during low-salt intake

Janus kinase (JAK) 2 is activated by ANG II in vitro and in vivo, and chronic blockade of JAK2 by the JAK2 inhibitor AG-490 has been shown recently to attenuate ANG II hypertension in mice. In this study, AG-490 was infused intravenously in chronically instrumented rats to determine if the blunted hypertension was linked to attenuation of the renal actions of ANG II. In male Sprague-Dawley rats, after a control period, ANG II at 10 ng·kg(-1)·min(-1) was infused intravenously with or without AG-490 at 10 ng·kg(-1)·min(-1) iv for 11 days. ANG II infusion (18 h/day) increased mean arterial pressure from 91 ± 3 to 168 ± 7 mmHg by day 11. That response was attenuated significantly in the ANG II + AG-490 group, with mean arterial pressure increasing only from 92 ± 5 to 127 ± 3 mmHg. ANG II infusion markedly decreased urinary sodium excretion, caused a rapid and sustained decrease in glomerular filtration rate to ～60% of control, and increased renal JAK2 phosphorylation; all these responses were blocked by AG-490. However, chronic AG-490 treatment had no effect on the ability of a separate group of normal rats to maintain normal blood pressure when they were switched rapidly to a low-sodium diet, whereas blood pressure fell dramatically in losartan-treated rats on a low-sodium diet. These data suggest that activation of the JAK/STAT pathway is critical for the development of ANG II-induced hypertension by mediating its effects on renal sodium excretory capability, but the physiological control of blood pressure by ANG II with a low-salt diet does not require JAK2 activation.     

Attenuated renal vascular responses to acute angiotensin II infusion in smooth muscle-specific Na+/Ca2+ exchanger knockout mice

Recent studies in smooth muscle-specific Na(+)/Ca(2+) exchanger-1 knockout (NCX1(sm-/-)) mice reveal reduced arterial pressure and impaired myogenic responses compared with heterozygous littermates. In this study, we determined renal function in male anesthetized NCX1(sm-/-) mice and NCX1 heterozygous (NCX1(+/-)) littermates before and during acute ANG II infusions. Systolic blood pressure in awake mice was lower in NCX1(sm-/-) mice compared with NCX1(+/-) mice (119 ± 4 vs. 131 ± 3 mmHg, P < 0.05). Acute ANG II infusions (5 ng·min(-1)·g(-1) body wt) increased mean arterial pressure in anesthetized NCX1(+/-) (109 ± 2 to 134 ± 3 mmHg, P < 0.001, n = 8) and NCX1(sm-/-) (101 ± 8 to 129 ± 8 mmHg, P < 0.01, n = 6) mice to a similar extent (Δ25 ± 1 vs. Δ28 ± 4 mmHg, P > 0.05). In response to ANG II infusions, PAH clearance (C(PAH)) decreased from 1.39 ± 0.27 to 0.98 ± 0.22 ml·min(-1)·g(-1) (P < 0.05) and glomerular filtration rate (GFR) was reduced from 0.50 ± 0.09 to 0.32 ± 0.06 ml·min(-1)·g(-1) (P < 0.05) in NCX1(+/-) mice. In contrast, the NCX1(sm-/-) did not exhibit significant reductions in either C(PAH) (1.16 ± 0.30 to 1.22 ± 0.34 ml·min(-1)·g(-1), P > 0.05) or GFR (0.48 ± 0.08 to 0.41 ± 0.05 ml·min(-1)·g(-1), P > 0.05) during acute ANG II infusions. Using flometry to measure renal blood flow continuously, NCX1(sm-/-) mice had significantly attenuated responses to ANG II infusions (-34.2 ± 3.9%, P < 0.05) compared with those in NCX1(+/-) mice (-48 ± 2%) or in wild-type mice (-69 ± 7%). These data indicate that renal vascular responses to ANG II are attenuated in NCX1(sm-/-) mice compared with NCX1(+/-) mice and that NCX1 contributes to the renal vasoconstriction response to acute ANG II infusions.     

Aldosterone and the kidney: rapid regulation of renal microcirculation

Recent studies provide evidence that aldosterone (Aldo) accelerates hypertension, proteinuria and glomerulosclerosis in animal models of chronic renal failure. Although the underlying mechanisms are not well defined, Aldo may exert these deleterious renal effects by elevating renal vascular resistance (RVR) and glomerular capillary pressure (P(GC)). To test this possibility, we studied the action of Aldo on rabbit afferent (Af-) and efferent arterioles (Ef-Arts), crucial vascular segments to the control of glomerular hemodynamics. Aldo caused rapid (within 5 min) constriction in both arterioles. The constriction was not affected by spironolactone but was reproduced by membrane-impermeable albumin-conjugated Aldo, suggesting that vasoconstrictor actions are non-genomic. This notion was further supported by the finding that neither actinomycin D nor cycloheximide had effect. The vasoconstrictor action of Aldo on Af-Arts was inhibited by nifedipine (L-type calcium channel blocker), whereas that on Ef-Arts was inhibited by efonidipine (both L- and T-type calcium channel blocker) but not nifedipine. Disrupting the endothelium or nitric oxide (NO) synthesis inhibition augmented the vasoconstriction in Af-Arts, demonstrating that endothelium-derived NO modulates the vasoconstrictor actions of Aldo. Thus, Aldo causes non-genomic vasoconstriction via calcium mobilization thorough L- or T-type calcium channels in Af- or Ef-Arts, respectively. These vasoconstrictor actions on the glomerular microcirculation may play an important role in the pathophysiology and progression of renal diseases by elevating RVR and P(GC), especially when endothelium functions are impaired. In addition to our study, this review describes recent findings on the rapid cardiovascular actions of Aldo, with a particular attention to the renal hemodynamics.     

Predominant postglomerular vascular resistance response to reflex renal sympathetic nerve activation during ANG II clamp in rabbits

We have shown previously that a moderate reflex increase in renal sympathetic nerve activity (RSNA) elevated glomerular capillary pressure, whereas a more severe increase in RSNA decreased glomerular capillary pressure. This suggested that the nerves innervating the glomerular afferent and efferent arterioles could be selectively activated, allowing differential control of glomerular capillary pressure. A caveat to this conclusion was that intrarenal actions of neurally stimulated ANG II might have contributed to the increase in postglomerular resistance. This has now been investigated. Anesthetized rabbits were prepared for renal micropuncture and RSNA recording. One group (ANG II clamp) received an infusion of an angiotensin-converting enzyme inhibitor (enalaprilat, 2 mg/kg bolus plus 2 mg.kg(-1).h(-1)) plus ANG II ( approximately 20 ng.kg(-1).min(-1)), the other vehicle. Measurements were made before (room air) and during 14% O(2). Renal blood flow decreased less during ANG II clamp compared with vehicle [9 +/- 1% vs. 20 +/- 4%, interaction term (P(GT)) < 0.05], despite a similar increase in RSNA in response to 14% O(2) in the two groups. Arterial pressure and glomerular filtration rate were unaffected by 14% O(2) in both groups. Glomerular capillary pressure increased from 33 +/- 1 to 37 +/- 1 mmHg during ANG II clamp and from 33 +/- 2 to 35 +/- 1 mmHg in the vehicle group before and during 14% O(2), respectively (P(GT) < 0.05). During ANG II clamp, postglomerular vascular resistance was still increased in response to RSNA during 14% O(2), demonstrating that the action of the renal nerves on the postglomerular vasculature was independent of the renin-angiotensin system. This further supports our hypothesis that increases in RSNA can selectively control pre- and postglomerular vascular resistance and therefore glomerular ultrafiltration.     

Angiotensin II AT1 receptors preserve vasodilator reactivity in skeletal muscle resistance arteries

Resistance arteries (100-150 microm) were isolated from the gracilis muscle of normotensive Sprague-Dawley rats placed on a high-salt (HS) diet (4.0% NaCl) for 3-7 days. Exposure to the HS diet eliminated vascular relaxation in response to hypoxia (PO2 reduction to 35-40 Torr) and iloprost, a stable analog of prostacyclin. Vasodilator responses were restored in arteries isolated from chronically instrumented HS rats receiving a continuous intravenous infusion of either angiotensin II (ANG II; 5-6 ng x kg(-1) x min(-1)) or ANG II plus the AT2 receptor blocker PD-123319 (5 microg x kg(-1) x min(-1)) for 3 days before the isolated vessel studies. In contrast, coinfusion of the AT1 receptor blocker losartan (20 microg x kg(-1) x min(-1)) or coinfusion of both receptor blockers with ANG II eliminated the protective effect of ANG II to restore dilator responses to hypoxia and iloprost. Neither a HS diet nor ANG II infusion affected the dilation of gracilis arteries in response to direct activation of adenylyl cyclase by forskolin, suggesting that the effect of both the HS diet and the ANG II on the vasculature is mediated upstream from second messenger systems. These findings indicate that the protective effect of ANG II to maintain vasodilator reactivity in resistance arteries of rats on a HS diet is mediated via the AT1 receptor subtype.     

Hormonal regulation of renal sodium and water excretion during normotensive sodium loading in conscious dogs

Saline was infused intravenously for 90 min to normal, sodium-replete conscious dogs at three different rates (6, 20, and 30 micromol x kg(-1) x min(-1)) as hypertonic solutions (HyperLoad-6, HyperLoad-20, and HyperLoad-30, respectively) or as isotonic solutions (IsoLoad-6, IsoLoad-20, and IsoLoad-30, respectively). Mean arterial blood pressure did not change with any infusion of 6 or 20 micromol x kg(-1) x min(-1). During HyperLoad-6, plasma vasopressin increased by 30%, although the increase in plasma osmolality (1.0 mosmol/kg) was insignificant. During HyperLoad-20, plasma ANG II decreased from 14+/-2 to 7+/-2 pg/ml and sodium excretion increased markedly (2.3+/-0.8 to 19+/-8 micromol/min), whereas glomerular filtration rate (GFR) remained constant. IsoLoad-20 decreased plasma ANG II similarly (13+/-3 to 7+/-1 pg/ml) concomitant with an increase in GFR and a smaller increase in sodium excretion (1.9+/-1.0 to 11+/-6 micromol/min). HyperLoad-30 and IsoLoad-30 increased mean arterial blood pressure by 6-7 mm Hg and decreased plasma ANG II to approximately 6 pg/ml, whereas sodium excretion increased to approximately 60 micromol/min. The data demonstrate that, during slow sodium loading, the rate of excretion of sodium may increase 10-fold without changes in mean arterial blood pressure and GFR and suggest that the increase may be mediated by a decrease in plasma ANG II. Furthermore, the vasopressin system may respond to changes in plasma osmolality undetectable by conventional osmometry.     

p22phox in the macula densa regulates single nephron GFR during angiotensin II infusion in rats

Angiotensin II (ANG II) infusion increases renal superoxide (O(2)(-)) and enhances renal vasoconstriction via macula densa (MD) regulation of tubuloglomerular feedback, but the mechanism is unclear. We targeted the p22(phox) subunit of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) with small-interfering RNA (siRNA) to reduce NADPH oxidase activity and blood pressure response to ANG II in rats. We compared single nephron glomerular filtration rate (SNGFR) in samples collected from the proximal tubule (PT), which interrupts delivery to the MD, and from the distal tubule (DT), which maintains delivery to the MD, to assess MD regulation of GFR. SNGFR was measured in control and ANG II-infused rats (200 ng.kg(-1).min(-1) for 7 days) 2 days after intravenous injection of vehicle or siRNA directed to p22(phox) to test the hypothesis that p22(phox) mediates MD regulation of SNGFR during ANG II. The regulation of SNGFR by MD, determined by PT SNGFR-DT SNGFR, was not altered by siRNA in control rats (control + vehicle, 13 +/- 1, n = 8; control + siRNA, 12 +/- 2 nl/min, n = 8; not significant) but was reduced by siRNA in ANG II-treated rats (ANG II + vehicle, 13 +/- 2, n = 7; ANG II + siRNA, 7 +/- 1 nl/min, n = 8; P < 0.05). We conclude that p22(phox) and NADPH oxidase regulate the SNGFR during ANG II infusion via MD-dependent mechanisms.     

Effects of angiotensin II on regional afferent and efferent arteriole dimensions and the glomerular pole

The diversity of renal arteriole diameters in different cortical regions has important consequences for control of glomerular capillary pressure. We examined whether intrarenal angiotensin II (ANG II; 0.1, 1, or 5 ng. kg(-1). min(-1)) in anesthetized rabbits acts preferentially on pre- or postglomerular vessels using vascular casting. ANG II produced dose-related reductions in afferent and efferent diameters in the outer, mid, and inner cortex, without effecting arterial pressure. Afferent diameter decreased more than efferent in the outer and mid cortex (P < 0.05) but by a similar extent in juxtamedullary nephrons (P = 0.58). Calculated efferent resistance increased more than afferent, especially in the outer cortex (127 vs. 24 units; 5 ng. kg(-1). min(-1) ANG II). ANG II produced significant dose-related increases in the distance between the arterioles at the entrance to the glomerular pole in all regions. Thus afferent diameter decreased more in response to ANG II, but efferent resistance rose more due to smaller resting luminal dimensions. The results also indicate that glomerular pole dimensions change in response to ANG II.     

Volume expansion during acute angiotensin II receptor (AT(1)) blockade and NOS inhibition in conscious dogs

The responses to AT(1)-receptor blockade (candesartan 1 mg/kg) and to concomitant volume expansion (saline 35 ml/kg for 90 min) with and without nitric oxide synthase (NOS) inhibition (N(G)-nitro-L-arginine methyl ester 30 microg small middle dot kg(-1) small middle dot min(-1)) were investigated in separate experiments in normal dogs. AT(1) blockade decreased arterial pressure (106 +/- 4 to 96 +/- 5 mmHg) and increased glomerular filtration rate (GFR) by 17% and sodium excretion threefold. NOS inhibition increased arterial pressure (103 +/- 3 to 116 +/- 3 mmHg) and decreased GFR by 21% and reduced sodium excretion by some 80%. Volume expansion increased arterial pressure significantly in all series involving this procedure, most pronounced during combined AT(1) blockade and NOS inhibition (21 +/- 4 mmHg). Volume expansion during AT(1) blockade elicited marked natriuresis (26 +/- 11 to 274 +/- 55 micromol/min) that was severely reduced by concomitant NOS inhibition (10 +/- 3 to 45 +/- 11 micromol/min), but still much larger than that seen with volume expansion during NOS inhibition alone (2 +/- 1 to 23 +/- 7 micromol/min). Volume expansion during AT(1) blockade increased GFR (+30%), less so during combined AT(1) blockade and NOS inhibition (+13%), but it did not increase GFR significantly (P = 0.07) during NOS inhibition alone. Plasma ANG II increased greater than sevenfold with AT(1) blockade and doubled with NOS inhibition (paired t-test, P < 0.05), whereas it decreased by 50-80% during volume expansion irrespective of pretreatment, i.e., during NOS inhibition, volume expansion did not generate subnormal plasma ANG II concentrations. In conclusion, 1) acute AT(1) blockade leads to hyperfiltration, natriuresis, and hyperresponsiveness to volume expansion, 2) these responses are >85% inhibitable by unspecific NOS inhibition, and 3) NOS inhibition alone is followed by increases in plasma ANG II, hypofiltration, and severe antinatriuresis that may be counterbalanced but not overwhelmed by volume expansion. Thus NOS inhibition virtually abolishes the volume expansion natriuresis, at least in part, due to the lack of appropriate inhibition of the renin-angiotensin-aldosterone system.     

The cerebrovascular dysfunction induced by slow pressor doses of angiotensin II precedes the development of hypertension

Hypertension alters cerebrovascular regulation and increases the brain's susceptibility to stroke and dementia. We investigated the temporal relationships between the arterial pressure (AP) elevation induced by "slow pressor" angiotensin II (ANG II) infusion, which recapitulates key features of human hypertension, and the resulting cerebrovascular dysfunction. Minipumps delivering saline or ANG II for 14 days were implanted subcutaneously in C57BL/6 mice (n = 5/group). Cerebral blood flow was assessed by laser-Doppler flowmetry in anesthetized mice equipped with a cranial window. With ANG II (600 ng · kg(-1) · min(-1)), AP started to rise after 9 days (P < 0.05 vs. saline), remained elevated at 11-17 days, and returned to baseline at 21 days (P > 0.05). ANG II attenuated the cerebral blood flow increase induced by neural activity (whisker stimulation) or endothelium-dependent vasodilators, an effect observed before the AP elevation (7 days), as well as after the hypertension subsided (21 days). Nonpressor doses of ANG II (200 ng · kg(-1) · min(-1)) induced cerebrovascular dysfunction and oxidative stress without elevating AP (P > 0.05 vs. saline), whereas phenylephrine elevated AP without inducing cerebrovascular effects. ANG II (600 ng · kg(-1) · min(-1)) augmented neocortical reactive oxygen species (ROS) with a time course similar to that of the cerebrovascular dysfunction. Neocortical application of the ROS scavenger manganic(I-II)meso-tetrakis(4-benzoic acid)porphyrin or the NADPH oxidase peptide inhibitor gp91ds-tat attenuated ROS and cerebrovascular dysfunction. We conclude that the alterations in neurovascular regulation induced by slow pressor ANG II develop before hypertension and persist beyond AP normalization but are not permanent. The findings unveil a striking susceptibility of cerebrovascular function to the deleterious effects of ANG II and raise the possibility that cerebrovascular dysregulation precedes the elevation in AP also in patients with ANG II-dependent hypertension.     

Angiotensin II-stimulated secretion of arginine vasopressin is inhibited by atrial natriuretic peptide in humans

We investigated the effect of the intravenous infusion of atrial natriuretic peptide (ANP) on the response of plasma arginine vasopressin (AVP) levels to intravenous infusion of angiotensin II (ANG II) in healthy individuals. Intravenous infusion of ANP (10 ng·kg(-1)·min(-1)) slightly but significantly decreased plasma AVP levels, while intravenous infusion of ANG II (10 ng·kg(-1)·min(-1)) resulted in slightly increased plasma AVP levels. ANG II infused significant elevations in arterial blood pressure and central venous pressure (CVP). Because the elevation in blood pressure could have potentially inhibited AVP secretion via baroreceptor reflexes, the effect of ANG II on blood pressure was attenuated by the simultaneous infusion of nitroprusside. ANG II alone produced a remarkable increase in plasma AVP levels when infused with nitroprusside, whereas the simultaneous ANP intravenous infusion (10 ng·kg(-1)·min(-1)) abolished the increase in plasma AVP levels induced by ANG II when blood pressure elevation was attenuated by nitroprusside. Thus, ANG II increased AVP secretion and ANP inhibited not only basal AVP secretion but also ANG II-stimulated AVP secretion in humans. These findings support the hypothesis that circulating ANP modulates AVP secretion, in part, by antagonizing the action of circulating ANG II.     

Hypersensitivity to acute ANG II in female growth-restricted offspring is exacerbated by ovariectomy

Female growth-restricted offspring are normotensive in adulthood. However, ovariectomy induces a marked increase in mean arterial pressure (MAP) that is abolished by renin angiotensin system (RAS) blockade, suggesting RAS involvement in the etiology of hypertension induced by ovariectomy in adult female growth-restricted offspring. Blockade of the RAS also abolishes hypertension in adult male growth-restricted offspring. Moreover, sensitivity to acute ANG II is enhanced in male growth-restricted offspring. Thus, we hypothesized that an enhanced sensitivity to acute ANG II may contribute to hypertension induced by ovariectomy in female growth-restricted offspring. Female offspring were subjected to ovariectomy (OVX) or sham ovariectomy (intact) at 10 wk of age. Cardio-renal hemodynamic parameters were determined before and after an acute infusion of ANG II (100 ng·kg(-1)·min(-1) for 30 min) at 16 wk of age in female offspring pretreated with enalapril (40 mg·kg(-1)·day(-1) for 7 days). Acute ANG II induced a significant increase in MAP in intact growth-restricted offspring (155 ± 2 mmHg, P < 0.05) relative to intact control (145 ± 4 mmHg). Ovariectomy augmented the pressor response to ANG II in growth-restricted offspring (163 ± 2 mmHg, P < 0.05), with no effect in control (142 ± 2 mmHg). Acute pressor responses to phenylephrine did not differ in growth-restricted offspring relative to control, intact, or ovariectomized. Furthermore, renal hemodynamic responses to acute ANG II were significantly enhanced only in ovariectomized female growth-restricted offspring. Thus, these data suggest that enhanced responsiveness to acute ANG II is programmed by intrauterine growth restriction and that sensitivity to acute ANG II is modulated by ovarian hormones in female growth-restricted offspring.     

Diuretic response to acute hypertension is blunted during angiotensin II clamp

Acute hypertension inhibits proximal tubule (PT) fluid reabsorption. The resultant increase in end proximal flow rate provides the error signal to mediate tubuloglomerular feedback autoregulation of renal blood flow and glomerular filtration rate and suppresses renal renin secretion. To test whether the suppression of the renin-angiotensin system during acute hypertension affects the magnitude of the inhibition of PT fluid and sodium reabsorption, plasma ANG II levels were clamped by infusion of the angiotensin-converting enzyme (ACE) inhibitor captopril (12 microg/min) and ANG II after pretreatment with the bradykinin B(2) receptor blocker HOE-140 (100 microg/kg bolus). Because ACE also degrades bradykinin, HOE-140 was included to block effect of accumulating vasodilatory bradykinins during captopril infusion. HOE-140 increased the sensitivity of arterial blood pressure to ANG II: after captopril infusion without HOE-140, 20 ng x kg(-1) x min(-1) ANG II had no pressor effect, whereas with HOE-140, 20 ng x kg(-1) x min(-1) ANG II increased blood pressure from 104 +/- 4 to 140 +/- 6 mmHg. ANG II infused at 2 ng x kg(-1) x min(-1) had no pressor effect after captopril and HOE-140 infusion ("ANG II clamp"). When blood pressure was acutely increased 50-60 mmHg by arterial constriction without ANG II clamp, urine output and endogenous lithium clearance increased 4.0- and 6.7-fold, respectively. With ANG II clamp, the effects of acute hypertension were reduced 50%: urine output and endogenous lithium clearance increased two- and threefold, respectively. We conclude that HOE-140, an inhibitor of the B(2) receptor, potentiates the sensitivity of arterial pressure to ANG II and that clamping systemic ANG II levels during acute hypertension blunts the magnitude of the pressure diuretic response.     

Aldosterone induces interleukin-18 through endothelin-1, angiotensin II, Rho/Rho-kinase, and PPARs in cardiomyocytes

Aldosterone (Aldo) is recognized as an important risk factor for cardiovascular diseases. IL-18 induces myocardial hypertrophy, loss of contractility of cardiomyocytes, and apoptosis leading myocardial dysfunction. However, so far, there have been few reports concerning the interaction between Aldo and IL-18. The present study examined the effects and mechanisms of Aldo on IL-18 expression and the roles of peroxisome proliferator-activated receptor (PPAR) agonists in rat cardiomyocytes. We used cultured rat neonatal cardiomyocytes stimulated with Aldo to measure IL-18 mRNA and protein expression, Rho-kinase, and NF-kappaB activity. We also investigated the effects of PPAR agonists on these actions. Aldo, endothelin-1 (ET-1), and angiotensin II (ANG II) increased IL-18 mRNA and protein expression. Mineralocorticoid receptor antagonists, endothelin A receptor antagonist, and ANG II receptor antagonist inhibited Aldo-induced IL-18 expression. Aldo induced ET-1 and ANG II production in cultured media. Moreover, Rho/Rho-kinase inhibitor and statin inhibited Aldo-induced IL-18 expression. On the other hand, Aldo upregulated the activities of Rho-kinase and NF-kappaB. PPAR agonists attenuated the Aldo-induced IL-18 expression and NF-kappaB activity but not the Rho-kinase activity. Our findings indicate that Aldo induces IL-18 expression through a mechanism that involves, at a minimum, ET-1 and ANG II acting via the Rho/Rho-kinase and PPAR/NF-kappaB pathway. The induction of IL-18 in cardiomyocytes by Aldo, ET-1, and ANG II might, therefore, cause a deterioration of the cardiac function in an autocrine and paracrine fashion. The inhibition of the IL-18 expression by PPAR agonists might be one of the mechanisms whereby the beneficial cardiovascular effects are exerted.     

Volume expansion during NOS substrate donation with L-arginine: regulatory offsetting of renal response?

The responses to infusion of nitric oxide synthase substrate (L-arginine 3 mg.kg(-1).min(-1)) and to slow volume expansion (saline 35 ml/kg for 90 min) alone and in combination were investigated in separate experiments. L-Arginine left blood pressure and plasma ANG II unaffected but decreased heart rate (6 +/- 2 beats/min) and urine osmolality, increased glomerular filtration rate (GFR) transiently, and caused sustained increases in sodium excretion (fourfold) and urine flow (0.2 +/- 0.0 to 0.7 +/- 0.1 ml/min). Volume expansion increased arterial blood pressure (102 +/- 3 to 114 +/- 3 mmHg), elevated GFR persistently by 24%, and enhanced sodium excretion to a peak of 251 +/- 31 micromol/min, together with marked increases in urine flow, osmolar and free water clearances, whereas plasma ANG II decreased (8.1 +/- 1.7 to 1.6 +/- 0.3 pg/ml). Combined volume expansion and L-arginine infusion tended to increase arterial blood pressure and increased GFR by 31%, whereas peak sodium excretion was enhanced to 335 +/- 23 micromol/min at plasma ANG II levels of 3.0 +/- 1.1 pg/ml; urine flow and osmolar clearance were increased at constant free water clearance. In conclusion, L-arginine 1) increases sodium excretion, 2) decreases basal urine osmolality, 3) exaggerates the natriuretic response to volume expansion by an average of 50% without persistent changes in GFR, and 4) abolishes the increase in free water clearance normally occurring during volume expansion. Thus L-arginine is a natriuretic substance compatible with a role of nitric oxide in sodium homeostasis, possibly by offsetting/shifting the renal response to sodium excess.     

The arterial depressor response to chronic low-dose angiotensin II infusion in female rats is estrogen dependent

The complex role of the renin-angiotensin-system (RAS) in arterial pressure regulation has been well documented. Recently, we demonstrated that chronic low-dose angiotensin II (ANG II) infusion decreases arterial pressure in female rats via an AT(2)R-mediated mechanism. Estrogen can differentially regulate components of the RAS and is known to influence arterial pressure regulation. We hypothesized that AT(2)R-mediated depressor effects evident in females were estrogen dependent and thus would be abolished by ovariectomy and restored by estrogen replacement. Female Sprague-Dawley rats underwent ovariectomy or sham surgery and were treated with 17β-estradiol or placebo. Mean arterial pressure (MAP) was measured via telemetry in response to a 2-wk infusion of ANG II (50 ng·kg(-1)·min(-1) sc) or saline. MAP significantly decreased in females treated with ANG II (-10 ± 2 mmHg), a response that was abolished by ovariectomy (+4 ± 2 mmHg) and restored with estrogen replacement (-6 ± 2 mmHg). Cardiac and renal gene expression of components of the RAS was differentially regulated by estrogen, such that overall, estrogen shifted the balance of the RAS toward the vasodilatory axis. In conclusion, estrogen-dependent mechanisms offset the vasopressor actions of ANG II by enhancing RAS vasodilator pathways in females. This highlights the potential for these vasodilator pathways as therapeutic targets, particularly in women.     

L-arginine-induced glomerular hyperfiltration response: the roles of insulin and ANG II

Infusion of L-arginine produces an increase in glomerular filtration via kidney vasodilation, correlating with increased kidney excretion of nitric oxide (NO) metabolites, but the specific underlying mechanisms are unknown. We utilized clearance and micropuncture techniques to examine the whole kidney glomerular filtration rate (GFR) and single nephron GFR (SNGFR) responses to 1) L-arginine (ARG), 2) ARG+octreotide (OCT) to block insulin release, 3) ARG+OCT+insulin (INS) infusion to duplicate ARG-induced insulin levels, and 4) losartan (LOS), an angiotensin AT-1 receptor blocker, +ARG+OCT. ARG infusion increased GFR, while increasing insulin levels. OCT coinfusion prevented this increase in GFR, but with insulin infusion to duplicate ARG induced rise in insulin, the GFR response was restored. Identical insulin levels in the absence of ARG had no effect on GFR. In contrast to ARG infusion alone, coinfusion of OCT with ARG reduced proximal tubular fractional and absolute reabsorption potentially activating tubuloglomerular feedback. Losartan infusion, in addition to ARG and OCT (LOS+ARG+OCT), restored the increase in both SNGFR and proximal tubular reabsorption, without increasing insulin levels. In conclusion, 1) hyperfiltration responses to ARG require the concurrent, modest, permissive increase in insulin; 2) inhibition of insulin release after ARG reduces proximal reabsorption and prevents the hyperfiltration response; and 3) inhibition of ANG II activity restores the hyperfiltration response, maintains parallel increases in proximal reabsorption, and overrides the arginine/octreotide actions.     

Enhanced renal expression of preproendothelin mRNA during chronic angiotensin II hypertension

The purpose of this study was to determine the role of endothelin in mediating the renal hemodynamic and arterial pressure changes observed during chronic ANG II-induced hypertension. ANG II (50 ng x kg(-1) x min(-1)) was chronically infused into the jugular vein by miniosmotic pump for 2 wk in male Sprague-Dawley rats with and without endothelin type A (ET(A))-receptor antagonist ABT-627 (5 mg x kg(-1) x day(-1)) pretreatment. Arterial pressure increased in ANG II rats compared with control rats (149 +/- 5 vs. 121 +/- 6 mmHg, P < 0.05, respectively). Renal expression of preproendothelin mRNA was increased by approximately 50% in both the medulla and cortex of ANG II rats. The hypertensive effect of ANG II was completely abolished in rats pretreated with the ET(A)-receptor antagonist (114 +/- 5 mmHg, P < 0.05). Glomerular filtration rate was decreased by 33% in ANG II rats, and this response was attenuated in rats pretreated with ET(A)-receptor antagonist. These data indicate that activation of the renal endothelin system by ANG II may play an important role in mediating chronic renal and hypertensive actions of ANG II.     

Attenuated renovascular constrictor responses to angiotensin II in adenosine 1 receptor knockout mice

In the present experiments we examined the renovascular constrictor effects of ANG II in the chronic and complete absence of A1 adenosine receptors (A1AR) using mice with targeted deletion of the A1AR gene. Glomerular filtration rate (GFR) was not different between A1AR +/+ and A1AR -/- mice under control conditions (450.5 +/- 60 vs. 475.2 +/- 62.5 microl/min) but fell significantly less in A1AR -/- mice during infusion of ANG II at 1.5 ng/min (A1AR +/+: 242 +/- 32.5 microl/min, A1AR -/-: 371 +/- 42 microl/min; P = 0.03). Bolus injection of 1, 10, and 100 ng of ANG II reduced renal blood flow and increased renal vascular resistance significantly more in A1AR +/+ than in A1AR -/- mice. Perfused afferent arterioles isolated from A1AR +/+ mice constricted in response to bath ANG II with an EC50 of 1.5 +/- 0.4 x 10(-10) mol/l, whereas a right shift in the dose-response relationship with an EC50 of 7.3 +/- 1.2 x 10(-10) mol/l (P < 0.05) was obtained in arterioles from A1AR -/- mice (P < 0.05). The expression of AT1A receptor mRNA was not different in kidney RNA from A1AR +/+ or A1AR -/- mice. We conclude that chronic A1AR deficiency diminishes the effectiveness of ANG II to constrict renal resistance vessels and to reduce GFR.