Biomedical subjects

G Rindi

Publications and source records attributed to G Rindi.

At least 163 records · Page 9Linked to original sources

PubMed1980

An improved method for the electrophoretic separation and fluorometric determination of thiamine and its phosphates in animal tissues.

An improved method for electrophoretic separation and fluorometric (or radiometric) determination of thiamine and thiamine mono-, di- and tri-phosphates in animal tissues (liver, small intestine, kidney, heart, brain) is described. The amount of total thiamine handled was 1.5-3.5 microgram. The procedure includes: acid excretion of the compounds from the tissue, deproteinization with TCA, purification of the extract on partially deactivated charcoal, elution with 10% n-propanol in 0.1 N formic acid, lyophilization, electrophoresis on gelatinized cellulose acetate strips, elution of the thiaminic bands with 50% ethanol and finally oxidation to thiochromes and reading of eluate fluorescence in a spectrofluorophotometer. The mean internal recovery was 83.3% and the external one 83.5%. Dephosphorylation of the T phosphates was rather scanty and each thiamine compound was comparably recovered (82.0-85.7%), apparently TTP being the worst and T the best recovered compound.

Animals↗

PubMed1979

Thiamin turnover rate in some areas of rat brain and liver: a preliminary note.

Thiamin turnover rates in some nervous structures and liver of rats were evaluated in a steady state condition, using thiamin- 14C as a tracer. The radioactivity contents were analyzed by means of a mamillary type compartmental model. Excluding the liver, turnover rate values of the nervous structures were ordered in the following sequence: sciatic nerve (0.58 microgram/g . h) less than cerebellum less than hypothalamus less than midbrain less than corpus striatum less than cerebral cortex (0.16 microgram/g . h).

Animals↗

PubMed1979

Thiamine intestinal transport and phosphorylation : a study in vitro of potential inhibitors of small intestinal thiamine-pyrophosphokinase using a crude enzymatic preparation.

Using as enzymatic source the cytoplasmatic fraction of enterocytes isolated from the rat small intestine, thiamine-pyrophosphokinase activity was studied with a radiometric method using [thiazole-2-(14)C] thiamine. The Km value for thiamine was 2.14 X 10(-6) M and V 0.87 nmol of thiamine pyrophosphate mg-1 protein h-1. Eleven thiamine structural analogs and derivatives were assayed for their inhibitory action on the small intestine thiamine-pyrophosphokinase activity. Their Ki values were : pyrithiamine, 2.25 X 10(-6) M; thiamine monophosphate, 4 X 10(-6) M; 2'-ethylthiamine, 8 X 10(-6) M; 2'-butylthiamine, 6 X 10(-6) M; chloroethylthiamine and dimethalium, 1.5 X 10(-5) M; amprolium, 1.8 X 10(-4) M; L-582571, 1.65 X 10(-4) M; oxythiamine, 4.2 X 10(-3) M. Of the miscellaneous compounds tested (toxopyrimidine, Na-pyrophosphate, choline, L-phenylalanine, ethyl-urethane and 5-fluorouracil), none had any inhibitory action on intestinal thiamine-pyrophosphokinase activity, even if used at concentrations hundred times higher than that of labelled thiamine.

Animals↗

PubMed1978

The action of inorganic phosphate on thiamin transport by rat everted jejunal sacs.

Rat everted jejunal sacs were incubated at 37 degree C in Krebs-Henseleit buffer, pH 7.4, containing thiazole-2- 14C-thiamine (0.2 micrometer), in the absence or in the presence of inorganic phosphate at a final concentration of 6mM. Control experiments under the same conditions, but without labeled thiamin were also carried out. In the intestinal sac wall, the content of labeled and endogenous (unlabeled) thiamin in the free and phosphorylated form was measured, while in the serosal fluid, total transported thiamin (labeled and endogenous) was evaluated. Accumulation in the enterocyte of inorganic phosphate, an inhibitor of thiamin pyrophosphate enzymatic hydrolysis, lowered the dephosphorylation of endogenous thiamin phosphates, both in the presence and in the absence of labeled thiamin. In the presence of labeled thiamin, the following results were observed: a) decreased labeled thiamin uptake and accumulation, both in the phosphorylated and free form; b) reduction of labeled thiamin transport to the serosal side; c) increase of endogenous thiamin exit from the intestinal cell. These findings seem to point out an important role of thiamin phosphorylation-dephosphorylation coupling in thiamin intestinal transport in vitro.

Animals↗

PubMed1978

Kinetics of D-histidine diffusion across rat intestine in vitro.

A five-compartment linear model for diffusion in vitro across rat jejunum has been proposed for the study of the kinetic constants of D-histidine transport. Once preliminary experiments using 2,4-dinitrophenol and L-methionine have proved that D-histidine gives rise to passive transport only, the validity of the model was tested and its parameters estimated through a best-fitting procedure by using experimental data concerning D-histidine transport. D-Histidine diffusion was studied in everted and unreverted loops mounted in an oxygenated bath system. Both mucosa to serosa and seroa to mucosa movements of D-histidine (3-30 mM) were evaluated by measuring chemically the amount of D-histidine transported into intestinal lumen every 5 min for 60 min. Results obtained proved that D-histidine transport in each direction (mucosa to seroa or seroa to mucosa) was dependent-concentration process. Nevertheless different values of gain and time constants were estimated for the transport in the two directions.

Animals↗

PubMed1977

Thiamine transport by human intestine in vitro.

Surgical specimens of human gastrointestinal mucosa and mucosa and muscle were incubated in vitro with thiamine-thiazole-214 C. Labelled thiamine uptake was uphill in mucosal tissues and downhill in muscle. Small intestinal mucosa accumulated labelled thiamine in a phosphorylated form, while gastric and colonic mucosa, as well an muscular layers of all gastrointestinal segments studied, did not.

Biological Transport↗

PubMed1977

Subcellular distribution of thiamine-pyrophosphokinase and thiamine-pyrophosphatase activities in rat isolated enterocytes.

Starting from mucosal cells, isolated from rat small intestine, subcellular fractionation was carried out. Four fractions were prepared and characterized by marker enzymes and electron microscopic examination: nuclei plus microvilli, mitochondria, microsomes and supernatant. Thiamine-pyrophosphokinase activity was localized mainly in the supernatant fraction, with minor amount in mitchondria and microsomes. On the contrary thiamine-pyrophosphatase activity was present only in the particulate fractions (especially in microsomes), being completely absent from the supernatant.

Animals↗

PubMed1975

Free thiamine as the likely precursor of endocellular thiamine phosphates in everted rings of rat jejunum.

Labeled and unlabeled (endogenous) free and phosphorylated thiamine were measured in isolated everted rings of rat jejunum in vitro during short incubation periods (1-10min). Shortly after the addition of thiamine-14C to the incubation medium, the intracellular specific activity of the free form was higher than the specific activity of the phosphorylated fraction. In the course of time this difference diminished and finally the two specific activities became equal. The conclusion was reached that free thiamine is the likely precursor of intracellular phosphorylated thiamine. Moreover evidence is presented which indicates that free thiamine entered actively into intestinal epithelial cells. Since free thiamine was modified into phosphorylated form inside the cells, its movement against the endocellular concentration gradient was noticeably favoured.

Animals↗

PubMed1973