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Biomedical subjects

R Riva

Publications and source records attributed to R Riva.

At least 109 records · Page 6Linked to original sources
PubMed1982

Rapid and simple GLC determination of valproic acid and ethosuximide in plasma of epileptic patients.

A GLC method for the determination of valproic acid and ethosuximide in plasma was developed. The procedure involved a single solvent extraction of drugs from acidified plasma samples, followed by a GLC injection of the unconcentrated organic phase. This rapid, sensitive, specific, and reproducible method has been used for 2 years for the routine determination of plasma levels of valproic acid and ethosuximide in epileptic patients who receive other antiepileptic drugs simultaneously.

Chromatography, Gas↗
PubMed1982

Determination of unbound valproic acid concentration in plasma by equilibrium dialysis and gas--liquid chromatography: methodological aspects and observations in epileptic patients.

An equilibrium dialysis technique for the separation of the free (unbound) concentration of valproic acid (VPA) in plasma is described together with a sensitive gas chromatographic assay for the quantitative determination of the drug in the dialysate. The overall coefficient of variation of the method was below 10%. By using a high permeability membrane, equilibration of the drug between the plasma and the buffer compartments was obtained after about 45 min at 37 degrees C. With this dialysis time, dilutional changes in the plasma compartment were negligible and there was no significant change in the plasma-free fatty acid (FFA) concentration. No passage of protein into the buffer solution was detected. When dialysis was prolonged for up to 4 h, a significant elevation in plasma FFA (with a corresponding rise in free VPA fraction) was observed. Storage of plasma samples at temperatures ranging from 4 to 37 degrees C for 8 h or longer before dialysis also resulted in an increased value of free VPA fraction and FFA concentration. The two effects were significantly correlated. The free fraction of VPA was found to increase with increasing total plasma concentration. This effect was observed both in vitro and in vivo in the plasma of 91 patients receiving chronic VPA therapy. The methodological problems of using equilibrium dialysis techniques for determining the free fraction of VPA are highlighted.

Blood Preservation↗
PubMed1982

Pseudo-elastica in alcoholic hepatic fibrosis: histochemical and ultrastructural aspects.

During the early phases of alcoholic hepatic fibrosis, histochemical studies show positivity to both specific elastin and the specific collagen stains at the level of the centrolobular vein, the portal triad and portacaval anastomosis. Ultrastructural investigation in the portacaval anastomosis demonstrates the presence of collagen fibrils and afibrillar material. Treatment with tannic acid increases the contrast of these structures. The possible correlations between histochemical and ultrastructural findings are discussed.

Collagen↗
PubMed1980

Rapid quantitative determination of underivatized carbamazepine, phenytoin, phenobarbital and p-hydroxyphenobarbital in biological fluids by packed column gas chromatography.

A method is described for measuring, without derivatization, the concentrations of phenobarbital, p-hydroxyphenobarbital, carbamazepine and phenytoin in biological fluids of epileptic patients undergoing long-term therapy. This method uses, at an isothermal temperature, a special column packing (GP-2% SP-2510-DA on 100-120 mesh Supelcoport). The lower limit of detection for all substances analyzed is 1 microgram/ml of biological material. The recovery of the compounds is about 95%, the reproducibility of the method is good (coefficient of variation, 4.3%). The mass spectra confirm the identity of substances eluting from the column. There is no interference from other commonly used antiepileptic drugs or endogenous substances. The method has the advantages of high specificity, sensitivity and rapidity and it appears to be suitable for the routine monitoring of blood and urine concentrations in patients receiving multi-drug therapy.

Adult↗
PubMed1979

Proteoglycans and their relationship with the other components of the rabbit aorta wall observed in two different experimental conditions.

An electron microscopic study of the aorta wall of rabbit was carried out employing electron microscopic histochemical methods aimed at examining the distribution of proteoglycans and their correlation with the other structural components of the aorta wall. The ultrastructural evidence of the proteoglycans has been obtained by treating the arterial wall with alcian blue stain and supporting this staining procedure with control enzyme treatments. Moreover, in order to attain a better interpretation of the ultrastructural findings, the arterial wall has been studied under 2 different experimental conditions, the 1st one being represented by an accentuated contraction of the vase's wall, following immersion in the fixator, the other one by an extreme distension of the wall, reached prior to fixation, subjecting the tissue to its tension limit of 700 dyn/mm2. This type of electron microscopic visualization of the proteoglycans following alcian blue treatment leads on to think that at least 2 distinct macromolecular entities of proteoglycans exist, each one having an unusual relationship with the other components of the arterial wall. Different site and types of interaction are to be noted for each of the 2 distinct ultrastructural proteoglycans entities.

Animals↗
PubMed1979

Ultrastructural observations on collagen and proteoglycans in the annulus fibrosus of the intervertebral disc.

Replicas of freeze-fractured collagen fibrils of peripheral and central parts of the annulus fibrosus of bovine intervertebral discs show microfibrils which run either arranged in parallel or in a helix with an inclination-angle ranging from 4 degrees to 8 degrees. According to results of freeze-fracutred tissues, thin sections of specimens treated with 4M guanidinium chloride show collagen fibrils with a parallel or a slightly wavy microfibrillar packing. Thin sections of specimens treated with alcian blue diluted in MgCl2 critical electrolyte solutions reveal interfibrillar proteoglycan particles with a filamentous shape in the peripheral zones of the annulus fibrosus and a predominant leaf-like appearance in the inner ones. These observations are discussed with reference to previous data concerning the variation in composition from the peripheral to the inner parts of the annulus fibrosus.

Animals↗
PubMed1978

Pharmacokinetic studies on ditazole, a novel inhibitor of platelet aggregation.

The distribution of ditazole in blood and tissues of rats was determined by a simple GLC technique. Ditazole, after intravenous injection in rats (20 mg/kg), entered preferentially into the brain, the liver, and the heart in decreasing order. In the epididymal adipose tissue, the drug was present only in small amounts. Ditazole disappeared from the rat organs 4 hr after the treatment. The apparent ditazole half-life in rat blood was 41 min, the volume of distribution was 2.068 liters/kg, and the body clearance was 0.0345 liter/kg/min.

Animals↗