Nitric oxide in afferent arterioles after uninephrectomy depends on extracellular l-arginine

Uninephrectomy (UNX) causes hyperperfusion of the contralateral remaining kidney via increased nitric oxide (NO) synthesis. Although the exact mechanism remains largely unknown, we hypothesize that this would be localized to the afferent arteriole and that it depends on cellular uptake of l-arginine. The experiments were performed in rats 2 days (early) or 6 wk (late) after UNX and compared with controls (Sham) to study acute and chronic effects on NO metabolism. Renal blood flow was increased after UNX (21 ± 2 ml·min−1·kg−1 in sham, 30 ± 3 in early, and 26 ± 1 in late, P < 0.05). NO inhibition with Nω-nitro-l-arginine methyl ester hydrochloride (l-NAME) caused a greater increase in renal vascular resistance in early UNX compared with Sham and late UNX (138 ± 24 vs. 88 ± 10, and 84 ± 7%, P < 0.01). The lower limit of autoregulation was increased both in early and late UNX compared with Sham ( P < 0.05). l-NAME did not affect the ANG II-induced contraction of isolated afferent arterioles (AA) from Sham. AA from early UNX displayed a more pronounced contraction in response to l-NAME (−57 ± 7 vs. −16 ± 7%, P < 0.05) and in the absence of l-arginine (−41 ± 4%, P < 0.05) compared with both late UNX and Sham. mRNA expression of endothelial NO synthase was reduced, whereas protein expression was unchanged. Cationic amino acid transporter-1 and -2 mRNA was increased, while protein was unaffected in isolated preglomerular resistance vessels. In conclusion, NO-dependent hyperperfusion of the remaining kidney in early UNX is associated with increased NO release from the afferent arteriole, which is highly dependent on extracellular l-arginine availability.

Collagen-binding proteins in age-dependent changes in renal collagen turnover: microarray analysis of mRNA expression

Aging is associated with progressive structural and functional deterioration of the kidney. Among the morphological changes associated with renal aging is an accumulation of extracellular matrix (ECM) in the glomeruli and tubuloinsterstitium, which may ultimately lead to the development of renal fibrosis. The mechanisms governing the regulation of ECM metabolism during renal aging are only incompletely defined. We present data from a genome-wide mRNA expression study on renal tissue from 90 wk old male Wistar rats and 10 wk old controls using Illumina BeadArray cDNA microarray. Regulation of candidate gene products was verified by real-time PCR. Morphological changes were evaluated by routine histological methods. Activated fibroblasts were identified by their expression of alpha-smooth muscle actin and collagen I. Morphological analysis demonstrated an expansion of the tubulointerstitial compartment with increased amounts of fibrous collagen but no overt glomerular or tubular damage in the aged rats. Activated fibroblasts were readily detectable in the adventitial layer of large renal vessels in controls and were not found in the old animals. In agreement with this finding, gene expression analysis revealed significant downregulation of collagen I mRNA along with numerous other ECM components. Concomitantly, collagen-stabilizing proteins were induced, whereas matrix metalloproteinase 9, an enzyme involved in collagen breakdown, was reduced. In conclusion, our results suggest that ECM expansion during renal aging results from an augmented stabilization in conjunction with a reduced breakdown of collagen fibers. Collagen stabilizing proteins may be essential for the control of renal ECM turnover and the pathogenesis of kidney fibrosis.

Afferent arteriolopathy and glomerular collapse but not segmental sclerosis induce tubular atrophy in old spontaneously hypertensive rats

In chronic renal disease, the temporal and spatial relationship between vascular, glomerular and tubular changes is still unclear. Hypertension, an important cause of chronic renal failure, leads to afferent arteriolopathy, segmental glomerulosclerosis and tubular atrophy in the juxtamedullary cortex. We investigated the pathological changes of hypertensive renal disease in aged spontaneously hypertensive rats using a large number of serial sections, where we traced and analyzed afferent arteriole, glomerulus and proximal tubule of single nephrons. Our major finding was that both afferent arteriolopathy and glomerular capillary collapse were linked to tubular atrophy. Only nephrons with glomerular collapse (n = 13) showed tubules with reduced diameter indicating atrophy [21.66 ± 2.56 μm vs. tubules in normotensive Wistar Kyoto rats (WKY) 38.56 ± 0.56 μm, p < 0.05], as well as afferent arteriolar wall hypertrophy (diameter 32.74 ± 4.72 μm vs. afferent arterioles in WKY 19.24 ± 0.98 μm, p < 0.05). Nephrons with segmental sclerosis (n = 10) did not show tubular atrophy and tubular diameters were unchanged (35.60 ± 1.43 μm). Afferent arteriolar diameter negatively correlated with glomerular capillary volume fraction (r = −0.36) and proximal tubular diameter (r = −0.46) implying reduced glomerular and tubular flow. In line with this, chronically damaged tubules showed reduced staining for the ciliary protein inversin indicating changed ciliary signalling due to reduced urinary flow. This is the first morphological study on hypertensive renal disease making correlations between vascular, glomerular and tubular components of individual nephron units. Our data suggest that afferent arteriolopathy leads to glomerular collapse and reduced urinary flow with subsequent tubular atrophy.

Adenosine sensitization after angiotensin II stimulation in afferent arterioles from normal rats does not occur during two-kidney, one-clip hypertension

AIMS

G protein-coupled receptors such as the AT(1a) R are frequently subject to desensitization, extensively studied in cell culture but to small extent in hypertensive models. Recently, angiotensin II (ANG II)-induced desensitization was shown to last 10 min in isolated afferent arterioles (AAs), suggesting impact on ANG II vasoactivity. In the present study, we explored ANG II desensitization and effects of adenosine (Ado) in AAs from two-kidney, one-clip (2K1C) hypertensive rats. Our main hypothesis was that Ado affects ANG II contractility differently in 2K1C, because of persistently elevated levels of ANG II.

METHODS

Afferent arterioles were isolated with the agarose-infusion/enzyme-treatment technique from normotensive and 2K1C hypertensive rats, and stimulated with ANG II (10(-7) M) at baseline and re-stimulated after 20 or 40 min, with or without Ado (2.5 × 10(-5) M) in the vessel bath.

RESULTS

Afferent arterioles from normotensive rats re-stimulated with ANG II after 20 min displayed a blunted contraction (Δ12.8 ± 4.3%, P < 0.05), which disappeared when AAs were stimulated after 40 min (Δ2.7 ± 2.3%, NS), indicating that desensitization lasted for 30 ± 10 min. Ado augmented ANG II contractions after 20 min, but not after 40 min, suggesting that only de-sensitized vessels were affected. Similar experiments in AAs from the clipped and non-clipped kidneys revealed no desensitization when re-stimulated with ANG II after 20 and 40 min, and contractions were unaffected by Ado.

CONCLUSIONS

Reduced duration of desensitization in AAs from 2K1C may cause vessels to be sensitized longer and increase vasoconstriction. The present study demonstrates that Ado does not augment ANG II-induced contractions in AAs from 2K1C as in normotensive rats, possibly because of a reduced period of desensitization.

Sympathectomy suppresses tumor growth and alters gene-expression profiles in rat tongue cancer

Sympathetic nerves are known to affect carcinogenesis. Recently we found that sympathetic denervation decreases the size of rat tongue tumors. To identify genes involved in rat tongue carcinogenesis and to study the effect of sympathetic nerves on these genes, we compared gene-expression profiles in normal rat tongue (control) and in tumor-induced tongues with (SCGx) and without (Sham) bilateral sympathectomy. Significance analysis of microarrays revealed 280 genes (168 up-regulated, 112 down-regulated) that showed at least a twofold differential expression between Sham and SCGx tumors (false discovery rate < 5%). These included genes associated with cell adhesion, signaling, structure, proliferation, metabolism, angiogenesis, development, and immunity. Hierarchical clustering demonstrated that controls and sympathectomized tumors grouped together, while Sham tumors grouped separately. We identified 34 genes, known to be involved in carcinogenesis, that were not differentially expressed between sympathectomized tumors and control tongues, but which showed a significant change in expression in Sham tumors. Microarray results of 12 of these genes were confirmed by quantitative reverse transcription-polymerase chain reaction. In conclusion, sympathectomy significantly altered the gene-expression profile and inhibited tumor growth. The expression of several cancer genes were increased more than threefold in Sham tumors, but unaltered in the sympathectomized tumors when compared with controls, indicating that these genes may be of significance in rat tongue carcinogenesis.

AT1 receptor activation regulates the mRNA expression of CAT1, CAT2, arginase-1, and DDAH2 in preglomerular vessels from angiotensin II hypertensive rats

Previously, we found increased expression of l-arginine metabolizing enzymes in both kidneys from two-kidney, one-clip (2K1C) hypertensive rats (Helle F, Hultstrom M, Skogstrand T, Palm F, Iversen BM. Am J Physiol Renal Physiol 296: F78–F86, 2009). In the present study, we investigate whether AT1 receptor activation can induce the changes observed in 2K1C. Four groups of rats were infused with 80 ng/min ANG II or saline for 14 days and/or given 60 mg·kg−1·day−1 losartan. Gene expression was studied in isolated preglomerular vessels by RT-PCR. Dose-responses to ANG II were studied in isolated preglomerular vessels with and without acute NOS inhibition [10−4 mol/l NG-nitro-l-arginine methyl ester (l-NAME)]. Expressions of endothelial nitric oxide synthase (eNOS), caveolin-1, and arginase-2 were not changed by ANG II infusion. CAT1 (0.3 8 ± 0.07 to 0.73 ± 0.12, P < 0.05), CAT2 (1.14 ± 0.29 to 2.74 ± 0.48), DDAH2 (1.09 ± 0.27 to 2.3 ± 0.46), and arginase-1 (1.08 ± 0.17 to 1.82 ± 0.22) were increased in ANG II-infused rats. This was prevented by losartan treatment, which reduced the expression of eNOS (0.97 ± 0.26 to 0.37 ± 0.11 in controls; 0.8 ± 0.16 to 0.36 ± 0.1 in ANG II-infused rats) and caveolin-1 (2.49 ± 0.59 to 0.82 ± 0.24 in controls and 2.59 ± 0.61 to 1.1 ± 0.25 in ANG II-infused rats). ANG II (10−10 mol/l) caused vessels from ANG II-infused animals to contract to 53 ± 15% of baseline diameter and 90 ± 5% of baseline diameter in controls ( P < 0.05) and was further enhanced by l-NAME to 4 ± 4% of baseline diameter ( P < 0.05). In vivo losartan treatment reduced the reactivity of isolated vessels to 91 ± 2% of baseline in response to 10−7 mol/l ANG II compared with 82 ± 3% in controls ( P < 0.05) and prevented the increased responsiveness caused by ANG II infusion. In conclusion, CAT1, CAT2, DDAH2, and arginase-1 expression in renal resistance vessels is regulated through the AT1 receptor. This finding may be of direct importance for NOS and the regulation of preglomerular vascular function.

Angiotensin II-induced contraction is attenuated by nitric oxide in afferent arterioles from the nonclipped kidney in 2K1C

Two-kidney, one-clip (2K1C) is a model of renovascular hypertension where we previously found an exaggerated intracellular calcium (Ca(i)(2+)) response to ANG II in isolated afferent arterioles (AAs) from the clipped kidney (Helle F, Vagnes OB, Iversen BM. Am J Physiol Renal Physiol 291: F140-F147, 2006). To test whether nitric oxide (NO) ameliorates the exaggerated ANG II response in 2K1C, we studied ANG II (10(-7) mol/l)-induced calcium signaling and contractility with or without the NO synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME). In AAs from the nonclipped kidney, l-NAME increased the ANG II-induced Ca(i)(2+) response from 0.28 +/- 0.05 to 0.55 +/- 0.09 (fura 2, 340 nm/380 nm ratio) and increased contraction from 80 +/- 6 to 60 +/- 6% of baseline (P < 0.05). In vessels from sham and clipped kidneys, l-NAME had no effect. In diaminofluorescein-FM diacetate-loaded AAs from the nonclipped kidney, ANG II increased NO-derived fluorescence to 145 +/- 34% of baseline (P < 0.05 vs. sham), but not in vessels from the sham or clipped kidney. Endothelial NOS (eNOS) mRNA and ser-1177 phosphorylation were unchanged in both kidneys from 2K1C, while eNOS protein was reduced in the clipped kidney compared with sham. Cationic amino acid transferase-1 and 2 mRNAs were increased in 2K1C, indicating increased availability of l-arginine for NO synthesis, but counteracted by decreased scavenging of the eNOS inhibitor asymmetric dimethylarginine by dimethylarginine dimethylaminohydrolase 2. In conclusion, the Ca(i)(2+) and contractile responses to ANG II are blunted by NO release in the nonclipped kidney. This may protect the nonclipped kidney from the hypertension and elevated ANG II levels in 2K1C.

Tetradecylthioacetic acid downregulates cyclooxygenase 2 in the renal cortex of two-kidney, one-clip hypertensive rats

The effect of tetradecylthioacetic acid (TTA) on the cyclooxygenase (COX) system was investigated in two-kidney, one-clip (2K1C) hypertensive rats. The systolic blood pressure (BP) was increased 6 wk after clipping to 183 +/- 4 vs.127 +/- 3 mmHg in TTA-treated 2K1C rats. The COX1 protein expression was not affected either by the 2K1C procedure or by TTA treatment. COX2 expression was upregulated in both kidneys, but to a greater extent in the clipped kidney. COX2 activity was 16 +/- 3% in control and 38 +/- 2% (P < 0.001) in the clipped kidney, and COX2 protein expression was 1.3 +/- 0.04 in control and 1.6 +/- 0.12 in the clipped kidney (P = 0.006). TTA reduced COX2 activity to control levels. Subcutaneously infusion of a COX2 inhibitor did not reduce BP. Peroxisome proliferator-activated receptors (PPARs) were detected in both kidneys, and PPARdelta was upregulated in the nonclipped kidney after TTA treatment. PGE2 in renal cortex was increased in 2K1C (31 +/- 0.3 in the clipped and 28 +/- 0.2 pg/ml nonclipped kidney, P < 0.001 compared with control). TTA lowered the PGE2 to control levels. Renal blood flow (RBF) response to exogenous ANG II injected in the control and nonclipped kidney was exaggerated after indomethacin treatment but unchanged in the nonclipped kidney of the K1C TTA group. Overall, these results indicate that, after 6 wk of treatment, TTA downregulated the COX2 activity, which have potentially important effects on the regulation of renal hemodynamics but does not explain TTAs ability to lower BP.

Adenosine triphosphate increases the reactivity of the afferent arteriole to low concentrations of norepinephrine

Adenosine triphosphate (ATP) and norepinephrine (NE) interact in the control of blood flow in the kidney. A combined effect of NE and ATP has not been previously investigated at the level of the afferent arteriole (Af). We studied the effects of ATP on the contractile response of the Af to NE. Vascular reactivity to ATP, NE, and their combination was investigated in isolated perfused Af from mice. The roles of alpha-adrenoceptors and P2-ATP-receptors were investigated by use of specific agonists and antagonists. Cytosolic calcium was measured using the fluorescent calcium dye fura-2. ATP in concentrations from 10(-12) to 10(-4) mol/l induced transient contractions. NE constricted the Af in a dose-dependent manner and induced significant contractions at > 10(-7) mol/l. Treatment with ATP (10(-8) and 10(-6) mol/l) increased the NE response. Diameters were reduced by 20% already at 10(-11) mol/l NE during ATP treatment of 10(-6) mol/l. ATP increased the calcium response to NE significantly at 10(-8) and 10(-7)mol/l NE. The P2-type ATP receptor blocker pyridoxal-phosphate-6-azophenyl-2',4'-disulfonic acid (PPADS) (10(-5) mol/l) abolished the sensitization of the NE response by ATP. The alpha(1)-blocker prazosin (10(-7) mol/l) inhibited the ATP effect, as did the alpha 2-blocker yohimbine (10(-7) mol/l). Neither the phenylephrine- nor clonidine-induced concentration response curves was affected by ATP in the bath solution. Costimulation with ATP enhances the response of the Af to NE. This effect is mediated by increased cytosolic calcium. The enhancing effect involves P2-type ATP receptors and both alpha (1)- and alpha 2-adrenoceptors.

Moderate hypothermia induces a preferential increase in pancreatic islet blood flow in anesthetized rats

The aim of the study was to characterize the effects of induced moderate hypothermia on splanchnic blood flow, with particular reference to that of the pancreas and the islets of Langerhans. We also investigated how interference with the autonomic nervous system at different levels influenced the blood perfusion during hypothermia. For this purpose, hypothermia (body temperature of 28°C) was induced by external cooling, whereas normothermic (37.5°C) anesthetized Sprague-Dawley rats were used as controls. Some rats were pretreated with either propranolol, yohimbine, atropine, hexamethonium, or a bilateral abdominal vagotomy. Our findings suggest that moderate hypothermia elicits complex, organ-specific circulatory changes, with increased perfusion noted in the pylorus, as well as the whole pancreas and the pancreatic islets. The pancreatic islets maintain their high blood perfusion through mechanisms involving both sympathetic and parasympathetic mediators, whereas the increased pyloric blood flow is mediated through parasympathetic mechanisms. Renal blood flow was decreased, and this can be prevented by ganglionic blockade and is also influenced by β-adrenoceptors.