Microbial iron reduction compensates for phosphorus limitation in paddy soils

Limitation of rice growth by low phosphorus (P) availability is a widespread problem in tropical and subtropical soils because of the high content of iron (Fe) (oxyhydr)oxides. Ferric iron-bound P (Fe(III)-P) can serve as a P source in paddies after Fe(III) reduction to Fe(II) and corresponding H₂PO₄^- release. However, the relevance of reductive dissolution of Fe(III)-P for plant and microbial P uptake is still an open question. To quantify this, ³²P-labeled ferrihydrite (30.8 mg P kg^-1) was added to paddy soil mesocosms with rice to trace the P uptake by microorganisms and plants after Fe(III) reduction. Nearly 2% of ³²P was recovered in rice plants, contributing 12% of the total P content in rice shoots and roots after 33 days. In contrast, ³²P recovery in microbial biomass decreased from 0.5% to 0.08% of ³²P between 10 and 33 days after rice transplantation. Microbial biomass carbon (MBC) and dissolved organic C content decreased from day 10 to 33 by 8-54% and 68-77%, respectively, suggesting that the microbial-mediated Fe(III) reduction was C-limited. The much faster decrease of MBC in rooted (by 54%) vs. bulk soil (8-36%) reflects very fast microbial turnover in the rice rhizosphere (high C and oxygen inputs) resulting in the mineralization of the microbial necromass. In conclusion, Fe(III)-P can serve as small but a relevant P source for rice production and could partly compensate plant P demand. Therefore, the P fertilization strategies should consider the P mobilization from Fe (oxyhydr)oxides in flooded paddy soils during rice growth. An increase in C availability for microorganisms in the rhizosphere intensifies P mobilization, which is especially critical at early stages of rice growth.

Bile duct ligation and oxidative stress in the rat: effects in liver and kidney

In the liver, seven days of bile duct ligation (BDL) decreases the cytochrome P-450 content and the UDP-glucuronyl transferase activity. Also, a decrease in the water soluble antioxidant mechanism reflected in the activities of the enzymes superoxide dismutase (SOD), catalase and the glutathione peroxidase (GTPx) was found in the liver but not in the kidney. Despite an increase in the amount of the GSH in the liver, increased lipid peroxidation is produced in the BDL rats, as indicated by the levels of malondialdehyde (MDA). The kidney responded in a different way to cholestasis, decreasing only the UDP-glucuronyl transferase activity and increasing the levels of GSH and MDA. In the red blood cells the activity of the antioxidant enzymes SOD, GTPx and catalase and the content of GSH were not modulated by cholestasis. In conclusion, disturbance of the oxidant-antioxidant balance might be responsible for cholestatic liver injury and impaired renal function in BDL rats.

Renal effects of experimental obstructive jaundice: morphological and functional assessment

BACKGROUND

The pathophysiology of renal impairments occurring in obstructive jaundice has been extensively studied, but the underlying mechanism of these derangements remains unclear. The aim of the present study was to investigate the time-related morphological and functional changes occurring in the kidneys of rats undergoing obstructive jaundice.

METHODS

Histological examination, renal function assessment and determination of (Na + K)-ATPase activity were performed in the kidneys of rats 7, 14, and 21 days following bile duct ligation (BDL) or sham operation (sham).

RESULTS

Glomerular filtration rate was unaffected by BDL throughout the period of the study. Tubular effects occurred at days 7 and 14, being more marked at day 7, and consisted of an increase of about twice in the fractional excretion of sodium and chloride, paralleled by a decreased proximal and distal tubular reabsorption of sodium of about 50 and 40%, respectively. Natriuresis was consistent with augmentation of osmolar clearance but it was not associated with changes in the activity of renal (Na+ + K+)-ATPase. The ability to dilute urine was impaired at days 14 and 21 after BDL. Additionally, these effects were accompanied by decreased tubulointerstitial fibrosis and vasodilation of inner medullary capillaries. At day 21, the parameters of tubular function in BDL and sham groups were not significantly different.

CONCLUSIONS

These data support the view that raised natriuresis taking place in the initial 2 weeks following BDL is due mainly to tubular effects. The contribution of hemodynamic, paracrine and humoral mediators is discussed.

Modulation of peroxisomal and microsomal fatty acid oxidation by acetone. A comparative study between liver and kidney

The effect of acetone consumption on some microsomal and peroxisomal activities was studied in rat kidney and these results were compared with data from former investigations in liver. Acetone increased the microsomal lauric acid hydroxylation, the aminopyrine N-demethylation catalyzed by cytochrome P450 and the microsomal UDP-glucuronyltransferase activity. Also, acetone increased the peroxisomal beta-oxidation of palmitoyl CoA and catalase activities in kidney. These studies suggest that acetone is a common inducer of the microsomal and peroxisomal fatty acid oxidation, as previously shown in both starved and ethanol treated rats. Our results support the hypothesis that microsomal fatty acid omega-hydroxylation results in the generation of substrates being supplied for peroxisomal beta-oxidation. We propose that the final purpose of these linked fatty acid oxidations could be the catabolism of fatty acids or the generation of a substrate for the synthesis of glucose from fatty acids. This pathway would be triggered by acetone treatment in a similar way in liver and kidney.

Effect of ethanol ingestion on renal regulation of water and electrolytes

Ethanol may alter the homeostasis of water and electrolytes before the occurrence of liver damage able to explain these disorders. How the kidney may become involved in water diuresis or sodium and potassium retention has not been well elucidated. During the last decade, an increasing body of evidence has guided interest toward the relevance of the biochemical basis of ethanol-induced injury to the kidney. Multiple functional abnormalities of renal tubules may be associated with ethanol-induced changes in membrane composition and lipid peroxidation of these epithelial cells. Ethanol interferes with the carrier function by decreasing (Na+K)-ATPase activity, but this activity is enhanced by chronic exposure. Recently, it was reported that ethanol oxidation by the kidney is favored in chronic ethanol-treated rats, thereby suggesting a pathogenic role for acetaldehyde in the nephrotoxic effect of ethanol ingestion. Also, increased reactive oxygen species, partly generated from acetaldehyde oxidation, may contribute to the occurrence of oxidative stress. The pathophysiology of renal regulation of water and electrolytes of alcoholic disease is analyzed on the basis of recent advances in our knowledge concerning the biochemical effects of ethanol on the kidney.

Acute and chronic effect of ethanol on (Na + K)-ATPase activity and cyclic AMP response to vasopressin in rat papillary collecting duct cells

1. We evaluated the effects of ethanol on (Na + K)-ATPase activity and cAMP response to vasopressin in native and cultured rat papillary collecting duct (PCD) cells. 2. A significant increase in (Na + K)-ATPase and Mg(2+)-ATPase activities was found in PCD cells either isolated from chronic ethanol-fed rats or cultured in the presence of ethanol. 3. Acute treatment with ethanol resulted in a biphasic effect on the activity of (Na + K)-ATPase, which was enhanced below 1% ethanol and inhibited at higher concentrations. 4. Chronic ethanol treatment did not change the cAMP response of PCD cells to vasopressin. Acutely, in turn, this response was enhanced by ethanol per se. 5. It is suggested that the antinatriuretic effect of ethanol could be at least in part mediated by a (Na + K)-ATPase enhancement in PCD cells. Acutely, ethanol could normalize water balance by its peripheral effects on distal nephron.

Effects of chronic and acute ethanol exposure on renal (Na + K)-ATPase in the rat

1. We evaluated the effects of chronic ethanol consumption on the kinetic properties of renal (Na + K)-ATPase and compared them with acute inhibition by ethanol in vitro. 2. When adult rats were fed 20% ethanol for 10 weeks, renal (Na + K)-ATPase activity increased but the sensitivity of the enzyme to ethanol inhibition in vitro was not altered. 3. Vmax was increased by ethanol consumption, whereas K0.5 and nH were not changed. The kinetic parameters of Mg(2+)-ATPase were not affected under the same conditions. 4. We concluded that ethanol-induced tolerance or enhancement of renal (Na + K)-ATPase or both can be explained on the basis of an increase in Vmax.