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Biomedical subjects

F J Rivas

Publications and source records attributed to F J Rivas.

15 recordsLinked to original sources
PubMed2005

Adsorption of landfill leachates onto activated carbon. Equilibrium and kinetics.

The adsorption of stabilized leachates generated in a municipal landfill onto three commercial activated carbons has been investigated. Norit 0.8, Chemviron AQ40 and Picacarb 1240 have been used as adsorbents. Equilibrium experiments have been conducted to obtain the experimental isotherm profiles. Isotherms have been plotted based on the adsorption of general parameters, for instance chemical oxygen demand, total carbon, absorption at 410 nm and absorption at 254 nm. Different literature models and error functions have been used to adequately fit the experimental data. As a rule of thumb, three-parameter models do adjust experimental results better than two-parameter models. Norit 0.8 shows better adsorption characteristics than the rest of activated carbons, both in terms of contaminant level reduction of per unit mass of absorbent and in terms of the process kinetics.

Adsorption↗
PubMed2001

Oxidation of p-hydroxybenzoic acid by Fenton's reagent.

Fenton's reagent has been shown to be a feasible technique to treat phenolic-type compounds present in a variety of food processing industry wastewaters. A model compound, p-hydroxybenzoic acid was oxidised by continuously pumping two solutions of ferrous iron and hydrogen peroxide. Typical operating variables like reagent feeding concentrations and flowrate, temperature and pH were studied. A mechanism of reactions based on the classical Fenton's chemistry was assumed, and computed concentration profiles of the parent compound, ferrous ion and dihydroxybenzene were compared to experimental results. The model qualitatively predicted the influence of several operating variables, however, calculated results suggested the presence of parallel routes of substrate elimination and/or a initiating rate constant with a higher value. The low efficiency of a well-known hydroxyl radical scavenger (tert-butyl alcohol) also supports the contribution of oxidising species different from the hydroxyl radical to substrate removal. Further evidence of the presence of reactions different from the hydroxyl radical oxidation was observed from comparison of the simultaneous Fenton's or UV/H2O2 oxidations of p-hydroxybenzoic acid, tyrosol and p-coumaric acid.

Chromatography, High Pressure Liquid↗
PubMed2001

Treatment of olive oil mill wastewater by Fenton's reagent.

Wastewater from olive oil mills has been treated by means of the Fe(II)/H(2)O(2) system (Fenton's reagent). Typical operating variables such as reagent concentration (C(H(2)O(2)) = 1.0--0.2 M; C(Fe(II)) = 0.01--0.1 M) and temperature (T = 293--323 K) exerted a positive influence on the chemical oxygen demand and total carbon removal. The optimum working pH was found to be in the range 2.5--3.0. The exothermic nature of the process involved a significant increase of the temperature of the reaction media. The process was well simulated by a semiempirical reaction mechanism based on the classic Fenton chemistry. From the model, the reaction between ferric iron and hydrogen peroxide [k = 1.8 x 10(15) exp((-12,577 +/- 1248)/T)] was suggested to be the controlling step of the system. Also, the simultaneous inefficient decomposition of hydrogen peroxide [k = 6.3 x 10(12) exp((-11,987 +/- 2414)/T)] into water and oxygen was believed to play an important role in the process. On the basis of stoichiometric calculations for hydrogen peroxide consumption, an estimation of the process economy has been completed.

Hydrogen Peroxide↗
PubMed2000

Kinetic modelling of aqueous atrazine ozonation processes in a continuous flow bubble contactor.

The ozonation of atrazine in different waters (ultrapure and surface waters) has been studied in continuous bubble contactors with kinetic modelling purposes. Three ozonation processes have been considered: ozonation alone and combined with hydrogen peroxide or UV radiation. The kinetic models are based on a molecular and free radical mechanism of reactions, reaction rate and mass transfer data and non-ideal flow analysis models for gas and water phases through the contactors (the tanks in series model and the dispersion model). The models predict well the experimental concentrations of atrazine, dissolved ozone and hydrogen peroxide both at non-steady state and steady state regimes. From both experimental and calculated results, atrazine conversions are observed to be highly dependent on the nature of water where ozonation is carried out. As far as removal of atrazine and oxidation intermediates are concerned, ozone combined with UV radiation resulted in the most effective ozonation process among the three studied.

Atrazine↗
PubMed2000

Chemical and photochemical degradation of acenaphthylene. Intermediate identification.

Removal of acenaphthylene from water has been carried out by means of different treatments combining UV radiation, ozone and hydrogen peroxide. Ozonation alone or in conjunction with hydrogen peroxide (10(-3) M) resulted in the highest elimination rates. Thus, conversions as high as 95-100% were obtained in less than 3 min with an ozone dose of 4.1x10(-3) mol O(3) h(-1) (flow rate 2x10(-2) m(3) h(-1)). Slightly lower efficiencies were experienced when using systems containing UV radiation. By considering the kinetics of the direct photolysis of acenaphthylene and the UV/H(2)O(2) system the photochemical reaction quantum yield φ(A) (4.0+/-0.1x10(-3) mol/photon) and the rate constant of the reaction of acenaphthylene with the hydroxyl radical k(OH,A) (8.0+/-0.5x10(9) M(-1) s(-1)) were calculated. Intermediates identified by GC/MS were in many cases similar regardless of the oxidation treatment used. Most of these by-products constituted oxygenated species of the parent compound (mainly ketones, aldehydes and carboxylic acids) that further degraded to low molecular, harmless end products.

Acenaphthenes↗
PubMed1992

Adrenalectomy does not change CRF secretion induced by interleukin-1 from rat perifused hypothalami.

Interleukin-1 (IL-1) is a potent hypothalamic-pituitary-adrenal (H-P-A) axis activator. The hypothalamus is considered one of the main sites of action of IL-1 on the H-P-A axis, inducing CRF secretion, which is modulated by glucocorticoids. Glucocorticoids, which modulate CRF release by a negative feedback inhibition, have been postulated to exert a permissive action on the IL-1 effect on CRF secretion. Using a continuous perifusion system of rat hypothalami, the results of the present study indicate that at the same concentrations, IL-1 beta exerted a more potent effect than IL-1 alpha stimulating CRF secretion. The increase in hypothalamic CRF release induced by IL-1 was rapidly inhibited by both dexamethasone and corticosterone. However, adrenalectomy 2 or 8 days before did not modify CRF secretion induced by IL-1 from the in vitro perifused hypothalami. These data indicate that IL-1 does not seem to induce CRF secretion by interfering with an impeding action of glucocorticoids, although the cytokine effect is negatively modulated by corticosteroids.

Adrenalectomy↗
PubMed1992

Release of corticotropin-releasing factor from superfused rat hypothalami induced by interleukin-1 is not dependent on adrenergic mechanism.

Interleukin-1 (IL-1) is a potent activator of the hypothalamic-pituitary-adrenal (HPA) axis. The hypothalamus seems to be the most important site of action of IL-1 on the HPA axis, inducing corticotropin-releasing factor (CRF) secretion. Catecholamines are important modulators of CRF secretion. In turn, IL-1 stimulates catecholamine release from the hypothalamus. In the present study, we examined the possible involvement of hypothalamic catecholamines in the effect of IL-1 beta on hypothalamic CRF secretion, by using an in vitro rat hypothalami continuous perifusion system. Neither in vivo pretreatment with an inhibitor of catecholamine synthesis nor in vitro exposure to alpha- or beta-adrenoceptor antagonists (phenoxybenzamine or propranolol, respectively) nor combination of both treatments altered the effect of IL-1 on CRF secretion from superfused hypothalami. These data indicate that catecholamines are not involved in the in vitro stimulatory action of IL-1 on hypothalamic CRF secretion.

Adrenocorticotropic Hormone↗
PubMed1992

Role of arachidonic acid metabolism on corticotropin-releasing factor (CRF)-release induced by interleukin-1 from superfused rat hypothalami.

The present work shows that the corticotropin-releasing factor (CRF)-releasing activity of interleukin-1 (IL-1) is partially inhibited by a phospholipase A2 (mepacrine) or a cyclooxygenase (indomethacin) inhibitor, but is not affected by inhibition of the lypoxygenase pathway with norhydroguaiaretic acid. These results indicate that the metabolism of arachidonic acid plays an important role as mediator of the effects of IL-1 on CRF release. It is also shown that products of the cyclooxygenase activity such as prostaglandins can stimulate CRF secretion by a direct action on the hypothalamus. Whereas PGE2 failed to induce increases on CRF release, PGF2 alpha stimulated in a dose-dependent manner (21-340 nM), the CRF release from continuous perifused hypothalami. It is suggested that PGF2 alpha could be involved as a messenger in the hypothalamic CRF secretion induced by IL-1.

Animals↗
PubMed1992

Interleukin-1-beta induces pituitary adrenocorticotropin secretion: evidence for glucocorticoid modulation.

Using an in vitro continuous perifusion system, the effects of interleukin-1 (IL-1) on adrenocorticotropin (ACTH) secretion at the pituitary level were investigated. On one hand, we observed that IL-1 beta increases ACTH secretion from perifused anterior pituitary cells in a dose-dependent manner, between 1.5 and 6 pM. This stimulatory action of IL-1 on ACTH was significantly attenuated by a short in vitro dexamethasone pretreatment. This fact suggests a regulatory glucocorticoid negative feedback analogous to that observed upon the pituitary action of corticotropin-releasing factor (CRF). We also examined the effect of simultaneous treatment with IL-1 and CRF. The results indicated that the effect of IL-1 resulted additive to the CRF-induced ACTH secretion. It is concluded that the anterior pituitary could be an important site of IL-1 action to activate the hypothalamic-pituitary-adrenocortical axis function, and that this action is under an inhibitory glucocorticoid regulation.

Adrenocorticotropic Hormone↗
PubMed1992

Interleukin-2 induces corticotropin-releasing hormone release from superfused rat hypothalami: influence of glucocorticoids.

The present work shows that interleukin-2 (IL-2) is able to increase in a dose-dependent manner (25-100 U/ml) CRF release from continuous perifused hypothalami. The effects of IL-2 and IL-1 on CRF secretion are potentiated by the simultaneous action of the two cytokines at the hypothalamus. The stimulatory effect of IL-2 on CRF secretion is significantly inhibited by the presence of dexamethasone in the perifusion medium. However, the CRF response to IL-2 was similar in adrenalectomized animals and sham-operated rats. It is suggested that the action of IL-2 on hypothalamic CRF secretion is integrated in the communication between the immune system and the hypothalamic-pituitary-adrenocortical axis, and that such action is subjected to glucocorticoid negative feedback modulation. The mechanism underlying the effect of IL-2 on CRF release is unknown, but arachidonic acid metabolites do not seem to be involved, since neither a lipooxygenase (nordihidrogueretic acid) nor a cyclooxigenase (indomethacin) inhibitor affected the hypothalamic secretory response to IL-2.

Adrenalectomy↗
PubMed1991

Accumbens lesion in female rats increases mount rejection without modifying lordosis.

Ovariectomized Wistar rats received bilateral electrolytic (n = 24) or sham (n = 11) lesion of the nucleus accumbens. Following priming with estradiol benzoate (25 micrograms/rat) and progesterone (0.5 mg/rat) they were tested for sexual behavior with a stud male. Tests were carried out once prior to operation and twice postoperatively. Both lordosis and rejection behaviors as responses to male mount attempts were evaluated for each session. Proceptive patterns (hopping, darting and presenting) were also recorded. Females with accumbens lesion did not differ from control animals either with regard to lordosis or to soliciting behaviors. On the contrary, the lesioned group showed a statistically significant increase in rejection behavior in both postoperative sessions (p less than 0.05 and p less than 0.002). In conclusion, nucleus accumbens lesion dissociated the normal correlation between lordosis and rejection responses to male mount attempts without affecting soliciting behaviors. This finding is thought to be related to the hyperreactivity produced by nucleus accumbens lesion.

Aggression↗
PubMed1990

Effects of nucleus accumbens lesion on female rat sexual receptivity and proceptivity in a partner preference paradigm.

A partner preference paradigm, stud male vs estrous female, was used to study sexual behavior. Ovariectomized Wistar rats received bilateral electrolytic (n = 33) or sham (n = 16) lesion of the nucleus accumbens. Animals were tested in two different experimental situations, either with stimulus animals tethered (test with possibility of mating) or with stimulus animals behind a wire mesh (test without possibility of mating). Each test was carried out once prior to surgery and twice postoperatively following priming with estradiol benzoate and progesterone. Lordosis, rejection behaviors and soliciting patterns were scored in tests with tethered stimulus animals. The tendency of the experimental female to approach and remain in the vicinity of each stimulus animal was quantified to study the partner preference. Nucleus accumbens lesion increased the number of rejection responses to male mount attempts without modifying either receptivity estimated by lordosis reflex or soliciting behaviors. Control females showed a statistically significant preference for the male throughout the experiments. Lesioned females exhibit a preference for the male only in the test without sexual interaction possibility. This preference disappeared in the test with possibility of mating and it was even reversed when the male showed copulatory activity. These results, together with the absence of changes in lordosis behavior and soliciting activity, suggest that both the inversion in preference and the higher levels of mount rejections found in the lesioned animals are more likely attributable to hyperreactivity to the copulatory stimulus rather than an alteration in the female's rat sexual motivation.

Animals↗