University of Córdoba (Spain)

About: University of Córdoba (Spain) is a education organization based out in Cordova, Spain. It is known for research contribution in the topics: Population & Catalysis. The organization has 12006 authors who have published 22998 publications receiving 537842 citations. The organization is also known as: University of Córdoba (Spain) & Universidad de Córdoba.

Fast and slow phosphate sorption by goethite-rich natural materials

Abstract: Although phosphate sorption by goethite and other less-abundant Fe oxides strongly influences the concentration of this anion in the soil solution and aquatic environments, relatively little is known on the P-sorption characteristics of natural goethites. For this reason, we examined the P-sorption capacity and time course of P sorption of 10 goethite-rich soil, ferricrete and lake ore samples, in which the content and nature of mineral impurities were unlikely to affect P sorption significantly. Phosphate sorption could be adequately described by a modified Freundlich equation including a time term. The amount of P sorbed after 1 day of equilibration at a concentration of 1 mg P/liter ranged widely (0.36–2.04 /μmol P/m2). The total P sorbed after 75 days of equilibration varied less, in relative terms (1.62–3.18 μmol P/m2), i.e., a higher slow sorption tended to compensate for a lower initial (fast) sorption. Total sorbed P (X = 2.62, SD = 0.52 μmol P/m2) was similar to the sorption capacity of synthetic goethites, suggesting a common sorption mechanism and the predominance of one type of crystal face, which, according to previous transmission electron microscope observations, might be the (110). The extent of the slow reaction correlated to the ratio between micropore surface area and total surface area, as well as to oxalate-extractable Fe, which is an estimation of the ferrihydrite content. Ferrihydrite impurities might affect the slow reaction by contributing to the microporosity of some samples. Silicate adsorbed on the surface of the goethites was readily desorbed during phosphate sorption and did not significantly affect the extent of the slow sorption process.

Long-Term Tillage, Crop Rotation, and Nitrogen Fertilizer Effects on Wheat Yield under Rainfed Mediterranean Conditions

Abstract: The combined long-term effects of tillage method and crop rotation on crop yield have not been studied in rainfed systems under Mediterranean climates. A field study was conducted from 1988 to 1994 to determine the effects of tillage (TILL), crop rotation (ROT) and N fertilizer on wheat (triticum aestivum L.) yield in a rainfed Mediterranean region. Tillage treatments include no tillage (NT) and conventional tillage (CT). Crop rotations were wheat-sunflower (Helianthus annuus L.) (WS), wheat-chickpea (Cicer arietinum L.) (WCP), wheat-fababean (Vicia faba L.) (WFB), wheat-fallow (WF), and continuous wheat (CW), with N fertilizer rates of 50, 100, and 150 kg N ha -1 . A split-split plot design with four replications was used. Differences in rainfall during the growing season had a marked effect on wheat yield. Amount of rainfall during the vegetative period for wheat (November-February) was highly correlated with yield because of the high water-retention capacity of Vertisols (Typic Haploxerert). In dry years, wheat yield was greater under NT than under CT ; the opposite was true in wet years. The TILL x ROT interaction was also significant in the drought years ; the wheat yield under NT was greater for CW and the WFB and WF rotations than under CT. Wheat yields ranked by crop rotation were : WFB > WF >> WCP > WS >> CW. Wheat did not respond to N fertilizer when rainfall was below 450 mm during the growing season. Using these results strategies can be developed for establishing the N fertilizer rate applied to wheat as a function of rainfall, the preceding crop, and residual N in soil in order to optimize wheat yield and reduce nitrate pollution to groundwater.

High phosphate level directly stimulates parathyroid hormone secretion and synthesis by human parathyroid tissue in vitro.

Abstract: Phosphate retention plays an important role in the pathogenesis of secondary hyperparathyroidism in patients with renal failure. In in vitro studies, high extracellular phosphate levels directly stimulate PTH secretion in rat and bovine parathyroid tissue. The present study evaluates the effect of high phosphate levels on the secretion of PTH and the production of prepro PTH mRNA in human hyperplastic parathyroid glands. The study includes parathyroid glands obtained from patients with primary adenomas and from hemodialysis and kidney-transplant patients with diffuse and nodular secondary hyperplasia. The experiments were performed in vitro using small pieces of parathyroid tissue. The ability of high calcium levels to decrease PTH secretion was less in adenomas than in secondary hyperplasia; among the secondary hyperplasia, nodular was less responsive to an increase in calcium than diffuse hyperplasia. In diffuse hyperplasia, PTH secretion was increased in response to 3 and 4 mM phosphate compared with 2 mM phosphate, despite a high calcium concentration in the medium; prepro PTH mRNA levels increased after incubation in 4 mM phosphate. Similar results were obtained with nodular hyperplasia, except that the elevation of PTH secretion in response to 3 mM phosphate did not attain statistical significance. In adenomas, high calcium concentrations (1.5 mM) did not result in inhibition of PTH secretion, independent of the phosphate concentration, and the prepro PTH mRNA was not significantly increased by high phosphate levels. In conclusion, first, the PTH secretory response to an increase in calcium concentration is less in nodular than diffuse hyperplasia; second, high phosphate levels directly affect PTH secretion and gene expression in patients with advanced secondary hyperparathyroidism.

Oxidative stress in diabetic rats induced by streptozotocin: Protective effects of melatonin

Abstract: We have studied the effect of the administration of two doses of melatonin (melatonin 100 and melatonin 200 microg/kg bw) on diabetes and oxidative stress experimentally induced by the injection of streptozotocin (STZ) in female Wistar rats. STZ was injected as a single dose (60 mg/kg i.p. in buffered citrate solution, pH 4.0) and melatonin (melatonin 100, 100 microg/kg/day i.p.; melatonin 200, 200 microg/kg/day i.p.) beginning 3 days before diabetes induction and continuing until the end of the study (8 weeks). The parameters analysed to evaluate oxidative stress and the diabetic state were a) for oxidative stress, changes of lipoperoxides (i.e., malondialdehyde, MDA) in plasma and erythrocytes and the changes in reduced glutathione (GSH) in erythrocytes and b) for diabetes, changes in glycemia, lipids (triglycerides: TG; total cholesterol: TC; HDL-cholesterol, HDL-c), percentage of glycosylated hemoglobin (Hb%), and plasma fructosamine. The injection of STZ caused significant increases in the levels of glycemia, percentage of glycosylated hemoglobin, fructosamine, cholesterol, triglycerides, and lipoperoxides in plasma and erythrocytes, whereas it decreased the levels of HDL-c and the GSH content in erythrocytes. The melatonin 100 dose reduced significantly all these increases, except the percentage of glycosylated hemoglobin. With regard to the decreases of plasma HDL-c and GSH content in erythrocytes, this melatonin dose returned them to normal levels. The melatonin 200 dose produced similar changes, though the effects were especially noticeable in the decrease of glycemia (55% vs. diabetes), percentage of hemoglobin (P < 0.001 vs diabetes), and fructosamine (31% vs. diabetes). This dose also reversed the decreases of HDL-c and GSH in erythrocytes. Both doses of melatonin caused significant reduction of the percentage of glycosylated hemoglobin in those groups that were non-diabetic. These illustrate the protective effect of melatonin against oxidative stress and the severity of diabetes induced by STZ. In particular, this study confirms two facts: 1) the powerful antioxidant action of this pineal indole and 2) the importance of the severity of oxidative stress to maintain hyperglycemia and protein glycosylation, two pathogenetic cornerstones indicative of diabetic complications. Melatonin reduces remarkably the degree of lipoperoxidation, hyperglycemia, and protein glycosylation, which gives hope to a promising perspective of this product, together with other biological antioxidants, in the treatment of diabetic complications where oxidative stress, either in a high or in a low degree, is present.