Renal aging in WKY rats: changes in Na+,K+ -ATPase function and oxidative stress.

It has been suggested that alterations in Na(+),K(+)-ATPase mediate the development of several aging-related pathologies, such as hypertension and diabetes. Thus, we evaluated Na(+),K(+)-ATPase function and H(2)O(2) production in the renal cortex and medulla of Wistar Kyoto (WKY) rats at 13, 52 and 91 weeks of age. Creatinine clearance, proteinuria, urinary excretion of Na(+) and K(+) and fractional excretion of Na(+) were also determined. The results show that at 91 weeks old WKY rats had increased creatinine clearance and did not have proteinuria. Despite aging having had no effect on urinary Na(+) excretion, urinary K(+) excretion was increased and fractional Na(+) excretion was decreased with age. In renal proximal tubules and isolated renal cortical cells, 91 week old rats had decreased Na(+),K(+)-ATPase activity when compared to 13 and 52 week old rats. In renal medulla, 91 week old rats had increased Na(+),K(+)-ATPase activity, paralleled by an increase in protein expression of α(1)-subunit of Na(+),K(+)-ATPase. In addition, renal H(2)O(2) production increased with age and at 91 weeks of age renal medulla H(2)O(2) production was significantly higher than renal cortex production. The present work demonstrates that although at 91 weeks of age WKY rats were able to maintain Na(+) homeostasis, aging was accompanied by alterations in renal Na(+),K(+)-ATPase function. The observed increase in oxidative stress may account, in part, for the observed changes. Possibly, altered Na(+),K(+)-ATPase renal function may precede the development of age-related pathologies and loss of renal function.

Increased responsiveness to JNK1/2 mediates the enhanced H2O2-induced stimulation of Cl-/HCO3- exchanger activity in immortalized renal proximal tubular epithelial cells from the SHR.

We have previously demonstrated that exogenous H2O2 stimulates Cl(-)/HCO3(-) exchanger activity in immortalized renal proximal tubular epithelial (PTE) cells from both the Wistar-Kyoto (WKY) rat and the spontaneously hypertensive rat (SHR), this effect being more pronounced in SHR cells. The aim of the present study was to examine the mechanism of H2O2-induced stimulation of Cl(-)/HCO3(-) exchanger activity in WKY and SHR cells. It is now reported that the SHR PTE cells were endowed with an enhanced capacity to produce H2O2, comparatively with WKY cells and this was accompanied by a decreased expression of SOD2, SOD3, and catalase in SHR PTE cells. The stimulatory effect of H2O2 on the exchanger activity was blocked by SP600125 (JNK inhibitor), but not by U0126 (MEK1/2 inhibitor) or SB203580 (p38 inhibitor) in both cell lines. Basal JNK1 and JNK2 protein expression was higher in SHR PTE cells than in WKY PTE cells. H2O2 had no effect on p-JNK1/2 in WKY PTE cells over time. By contrast, H2O2 treatment resulted in a rapid and sustained increase in JNK1/2 phosphorylation in SHR PTE cells, which was completely abolished by apocynin. Treatment of SHR PTE cells with apocynin significantly decreased the H2O2-induced stimulation of Cl(-)/HCO3(-) exchanger activity. It is concluded that H2O2-induced stimulation of Cl(-)/HCO3(-) exchanger activity is regulated by JNK1/2, particularly by JNK2, in SHR PTE cells. The imbalance between oxidant and antioxidant mechanisms in SHR PTE cells enhances the response of JNK1/2 to H2O2, which contributes to their increased sensitivity to H2O2.

Uso do óxido crômico e do LIPE® na estimativa do consumo de matéria seca por bezerros de corte / Use of chromic oxide and LIPE® as external markers to estimate dry matter intake by beef calves

Avaliou-se a eficiência do óxido crômico e da lignina purificada e enriquecida (LIPE®), fornecidos uma vez ao dia, para a estimativa do consumo de matéria seca (CMS). Foram utilizados 12 bezerros de corte, de ambos os sexos, com uma média de idade de 210 dias e peso médio de 168kg, pastejando Brachiaria decumbens, distribuídos em um delineamento inteiramente ao acaso, em esquema de parcelas subdivididas. Os valores estimados de consumo, entre machos e fêmeas, foram semelhantes nos dois tratamentos. Entre os indicadores, as estimativas, da produção fecal e do consumo, foram menores para o óxido crômico. O CMS de forragem, o CMS total, o CMS em relação ao peso vivo e o CMS em relação ao peso metabólico, estimados pelos indicadores óxido crômico e LIPE®, foram, respectivamente, 2,03 e 4,50kg; 2,71 e 5,18kg; 1,62 e 3,10 por cento e 58,10 e 111,32g/kg PV0,75. O consumo estimado pelo LIPE® foi mais condizente com as exigências e com o desempenho observado nos animais.

Six male and six female calves, seven-month-old, averaging 168kg bw, grazing on Brachiaria decumbens, were used in a split plot design to compare the efficacy of two external markers: chromic oxide (Cr2O3) and purified and enriched lignin (LIPE®) simultaneously dosed once a day to predict dry matter intake (DMI). For both, Cr2O3 and LIPE®, no differences in DMI according to gender were observed. Comparing the efficacy of the two markers to predict fecal output and pasture intake, the estimates obtained with chromic oxide were lower. Forage DMI, total DMI, DMI as percentage of body weight, and DMI in relation to metabolic weight were: 2.03 and 4.50kg; 2.71 and 5.18kg; 1.62 and 3.10 percent, and 58.10 and 111.32g/kg bw0.75 for Cr2O3 and LIPE®, respectively. These results suggest that estimates obtained from LIPE® were more appropriate to the dry matter requirements and performance of the calves.

Oxidative stress and alpha1-adrenoceptor-mediated stimulation of the Cl-/HCO3- exchanger in immortalized SHR proximal tubular epithelial cells.

BACKGROUND AND PURPOSE: This study evaluated the signalling coupled to the alpha1-adrenoceptor-induced stimulation of the Cl-/HCO3- exchanger in hypertension. EXPERIMENTAL APPROACH: The Na+ -independent HCO3- transport system activity was assayed as the initial rate of pHi recovery after an alkaline load (CO2/HCO3 removal) in immortalized renal proximal tubular epithelial cells from spontaneously hypertensive rat (SHR) and their normotensive control (Wistar Kyoto rat; WKY). KEY RESULTS: Noradrenaline increased Cl-/HCO3- exchanger activity with EC50 values of 0.6 and 5.3 microM in SHR and WKY cells, respectively. These effects were abolished by prazosin, but not by yohimbine. Phenylephrine increased Cl-/HCO3- exchanger activity in SHR and WKY cells (EC50 of 2.6 and 4.9 microM, respectively). Phenylephrine-mediated increase in Cl-/HCO3- exchanger activity in WKY and SHR cells was inhibited by protein kinase C (PKC), MAPK/ERK kinase (MEK) and p38 mitogen-activated protein kinase (p38 MAPK) inhibitors. The expression of alpha1A- and alpha1B-adrenoceptors was identical in WKY and SHR cells. SHR cells generated more H2O2 than WKY cells. In SHR cells, the NADPH oxidase inhibitor apocynin reduced their increased ability to generate H2O2 and abolished their hypersensitivity to phenylephrine, but failed to affect basal Cl-/HCO3- exchanger activity. H2O2-dependent stimulation of Cl-/HCO3- exchange activity was significantly higher in SHR than in WKY cells. CONCLUSIONS AND IMPLICATIONS: Differences between WKY and SHR cells on their sensitivity to alpha1-adrenoceptor stimulation did not correlate with the abundance of alpha1A- and alpha1B-adrenoceptors and may be related to the increased generation of H2O2, which may amplify the response downstream of alpha1-adrenoceptor activation.