Biomedical subjects

R Tommasini

Publications and source records attributed to R Tommasini.

At least 19 recordsLinked to original sources

PubMed1998

An ABC-transporter of Arabidopsis thaliana has both glutathione-conjugate and chlorophyll catabolite transport activity.

An ABC-transporter of Arabidopsis thaliana exhibiting high sequence similarity to the human (MRP1) and yeast (YCF1) glutathione-conjugate transporters has been analysed and used to complement a cadmium-sensitive yeast mutant (DTY168) that also lacks glutathione-conjugate transport activity. Comparison of the hydrophobicity plots of this A. thaliana MRP-like protein with MRP1 and YCF1 demonstrates that the transmembrane domains are conserved, even at the N-terminus where sequence identity is low. Cadmium resistance is partially restored in the complemented ycf1 mutant, and glutathione-conjugate transport activity can be observed as well. The kinetic properties of the A. thaliana MRP-like protein (AtMRP3) are very similar to those previously described for the vacuolar glutathione-conjugate transporter of barley and mung bean. Furthermore, a hitherto undescribed ATP-dependent transport activity could be correlated with the gene product, i.e. vesicles isolated from the complemented yeast, but not from DTY168 or the wild type, take up the chlorophyll catabolite Bn-NCC-1. The results indicate that the product of the MRP-like gene of A. thaliana is capable of mediating the transport of the two different classes of compounds.

ATP-Binding Cassette Transporters↗

PubMed1997

Differential expression of genes coding for ABC transporters after treatment of Arabidopsis thaliana with xenobiotics.

ATP-binding cassette (ABC) transporters are thought to be involved in many cellular detoxification mechanisms. Performing a BLAST search, we found four distinct expressed sequence tags (EST) of Arabidopsis thaliana highly similar to the human and fungal glutathione-conjugate ABC transporters. We studied the expression of the corresponding genes in response to various xenobiotics in an effort to gain information on their function. The abundance of transcripts corresponding to one of the genes (EST1) was not affected by the various compounds tested, whereas the abundance of transcripts corresponding to the other three genes (EST2, EST3, EST4) was increased by 1-chloro-2,4-dinitrobenzene, primisulfuron and IRL 1803. Treatment of Arabidopsis with either primisufuron or IRL 1803 resulted in a more than 40-fold increase in EST2-specific transcripts.

ATP-Binding Cassette Transporters↗

PubMed1997

Modulation of pulmonary arterial input impedance during transition from inspiration to expiration.

We investigated whether respiration influences pulmonary arterial input impedance during transition from inspiration to expiration in five anesthetized, spontaneously breathing dogs. Impedance (Z) was separately assessed for heart beats occurring in inspiration, in expiration, and during the transition from inspiration to expiration (transitional beat). Transitional beats were scored by the ratio between the fraction of beat falling in expiration and the total beat duration [expiratory fraction (Efr)] to quantify their position within the transition. In transitional beats, input resistance linearly increased with Efr; Z modulus at the heart-rate frequency (fHR) decreased up to -50% for Efr = 50%. Z phase at fHR was greater than in inspiration for Efr <40% and lower for Efr >50%. Unlike blood flow velocity, mean value and first harmonic of pulmonary arterial pressure were correlated to Efr and paralleled the changes of input resistance and Z at fHR. This indicates that respiration influences Z through modifications in arterial pressure. The evidence of important respiratory influences on Z function may help the pathophysiological interpretation of dysfunctions of the right heart pumping action, such as the so-called cor pulmonale.

Animals↗

PubMed1996

The human multidrug resistance-associated protein functionally complements the yeast cadmium resistance factor 1.

A Saccharomyces cerevisiae strain with a disrupted yeast cadmium resistance factor (YCF1) gene (DTY168) is hypersensitive to cadmium. YCF1 resembles the human multidrug resistance-associated protein MRP (63% amino acid similarity), which confers resistance to various cytotoxic drugs by lowering the intracellular drug concentration. Whereas the mechanism of action of YCF1 is not known, MRP was recently found to transport glutathione S-conjugates across membranes. Here we show that expression of the human MRP cDNA in yeast mutant DTY168 cells restores cadmium resistance to the wild-type level. Transport of S-(2,4-dinitrobenzene)-glutathione into isolated yeast microsomal vesicles is strongly reduced in the DTY168 mutant and this transport is restored to wild-type level in mutant cells expressing MRP cDNA. We find in cell fractionation experiments that YCF1 is mainly localized in the vacuolar membrane in yeast, whereas MRP is associated both with the vacuolar membrane and with other internal membranes in the transformed yeast cells. Our results indicate that yeast YCF1 is a glutathione S-conjugate pump, like MRP, and they raise the possibility that the cadmium resistance in yeast involves cotransport of cadmium with glutathione derivatives.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1996

Does spontaneous respiration alter pulmonary artery input impedance?

The aim of this study was to determine whether spontaneous respiration influences pulmonary artery input impedance, a question that has received little attention in the literature. Impedance values were assessed during three different phases of the respiratory cycle, namely inspiration, expiration and postexpiration (i.e. the null respiratory flow period between expiration and the next inspiration) in five anaesthetized spontaneously breathing dogs. Firstly, impedance values during postexpiration were taken as the reference baseline, and compared with values obtained during inspiration and expiration. Then, differences between values in inspiration and in expiration were tested, taking impedance during inspiration as the baseline. Differences with respect to postexpiration were found for three parameters of input impedance: input resistance, characteristic impedance, and the frequency at the first zero-crossing of the impedance phase from negative to positive values (f(cross)). Input resistance was significantly lower in inspiration (85% of the baseline), characteristic impedance was significantly greater in inspiration and in expiration (112 and 119% respectively), and f(cross) was significantly lower in expiration (89%). By contrast, only input resistance differed significantly when inspiration was compared to expiration. Therefore, spontaneous respiration was shown to influence input impedance significantly. The observed changes in characteristic impedance and f(cross) might be explained by a stiffening of the pulmonary artery wall, due to neural and/or mechanical factors, during inspiration and expiration.

Animals↗

PubMed1994

A herbicide antidote (safener) induces the activity of both the herbicide detoxifying enzyme and of a vacuolar transporter for the detoxified herbicide.

In plants potentially toxic compounds are ultimately deposited in the large central vacuole. In this report we show that isolated barley mesophyll vacuoles take up the glucoside conjugate of the herbicide derivate [5-hydroxyphenyl]primisulfuron. Transport is stimulated by Mg-ATP and is distinct from that previously described for glutathione conjugates. Treatment of barley with different herbicide antidotes (safeners) revealed that the safener cloquintocet-mexyl doubles the vacuolar transport activities for both the glutathione and glucoside conjugates. Stimulation of the uptake of the metolachlor-glutathione conjugate was the result of an increased uptake velocity whereas the Km remained unaltered, suggesting that the higher activity was due to a higher expression of the transporter. These results indicate that modulation of vacuolar transport activities are an integral part of the detoxification mechanism of plants.

Acetamides↗

PubMed1988

[Which moments in the respiratory cycle have the most influence on right ventricular dynamics?].

The performance of the right heart during respiratory activity has mostly been studied in terms of changes in flow and pressure in pulmonary circulation. The aim of this study was to identify which moments of the respiratory cycle exert the greatest influence on right ventricular dynamics. Thus, the behaviour of the right ventricular systolic time intervals and pulmonary artery pressures, expressed both as intravascular (Piv) and transmural (Ptm), were investigated to this end. Investigations were carried out on 10 anesthetized spontaneously breathing beagle dogs using high-fidelity pressure transducers (MPC 500, Millar Instr.) and by making use of a computerized system of signal recording and analysis. Changes in right ventricular systolic time intervals were evident during transition from inspiration to expiration and at the beginning of expiration. In fact, compared to spontaneous post-expiratory pause values, the so-called Rapid Ejection and Slow Ejection Phases, and therefore the Total Ejection Period, were significantly shortened (p less than 0.01 for both) only at early expiration, whereas during the same phase of the respiratory cycle the Isovolumetric Contraction Time and the total Pre-ejection Period were significantly prolonged (p less than 0.01 for both). During the transition from inspiration to expiration, the right ventricular systolic "plateau" very often presented an ascending slant, i.e., reaching maximum pressure in late instead of early systole, as usually observed in the other moments of the respiratory cycle.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

Discrimination of the isozymes of human placental hexosaminidase by kinetic parameter estimation.

Human placental beta-N-acetylhexosaminidase (EC 3.2.1.52) (HEX) is a lysosomal glycosyl hydrolase with an acidic pH optimum. Four isozymes (HEX B, HEX I1, HEX I2, and HEX A) have been isolated from human placenta. HEX BA derived from the subunit rearrangement of HEX A was also prepared. To determine if the isozymes of hexosaminidase differ in their kinetic parameters, the conditions for 4-methylumbelliferyl-beta-D-N-acetylglucosaminide hydrolysis were optimized for each isozyme. The Km values were essentially similar and varied from 0.64 +/- 0.06 for HEX BA to 0.85 +/- 0.13 for HEX I1. The Vmax values were similar only for HEX I1 (3.90 +/- 0.28 kat kg-1) and HEX I2 (4.40 +/- 0.17). Vmax values varied significantly between HEX A (9.68 +/- 0.52), HEX B (8.00 +/- 0.75), HEX BA (4.81 +/- 0.17), and the HEX I values.

Electrophoresis, Polyacrylamide Gel↗

PubMed1985

A statistical comparison of parameter estimation for the Michaelis-Menten kinetics of human placental hexosaminidase.

To enable the most effective method of kinetic discrimination between a group of isozymes such as those of human placental hexosaminidases (HEX), three methods estimating the parameters of the Michaelis-Menten equation were evaluated. Computer-simulated experiments were performed under various conditions. They indicated that, in the presence of constant absolute or relative errors, the method of unweighted nonlinear least squares yielded slightly more precise and accurate parameters than the method of the direct linear plot. Parameters calculated from the Lineweaver-Burk plot were very imprecise and inaccurate. The direct linear plot was comparatively resistant to outlier observations; however, only when outliers were substantial did the method become superior to nonlinear least squares. The calculation of a confidence limit is necessary for the evaluation of any resulting differences in the kinetic parameters for a set of isozymes. This can easily be calculated from either the Lineweaver-Burk plot or the nonlinear least-squares method. However, those calculated from the Lineweaver-Burk plot are biased, especially at higher levels of experimental errors. Therefore, the nonlinear least-squares method is the one most suited for the discrimination of a group of enzymes based on their kinetic parameters.

Computers↗

PubMed1981

Comparative effects of indoprofen and indomethacin on rat hypothalamic prostaglandin-synthetase activity.

The inhibiting effects of indoprofen were compared with those of indomethacin on prostaglandin-synthetase activity in rat hypothalamus. A dose-dependent inhibition of PG-synthetase activity was obtained after intramuscular administration of both antiphlogistic agents; however, indoprofen was found more powerful. In conclusion, the present experiments provide additional evidence against the idea that pyrogen fever is due to the release of PG's of the E type within the hypothalamus since when comparing results obtained with the two antiphlogistic drugs used, no correlation exists between potency in inhibiting PG's synthesis and antipyretic activity.

Animals↗

PubMed1981

Preclinical studies on indoprofen, a new non-steroidal analgesic-antiinflammatory agent.

Indoprofen is an isoindoline derivative of phenylpropionic acid. At doses of 1-3 mg/kg it inhibited acute and subchronic experimental inflammation. Its strong analgesic activity lacks any specific CNS effect. The drug's pharmacological activity is directly related to inhibition of prostaglandin biosynthesis at the cyclo-oxygenase step. In carrageenin-induced oedema indoprofen and prednisolone had a synergistic anti-inflammatory effect, and indoprofen and acetylsalicylic acid showed an additive effect. Acute and chronic toxicity of indoprofen was determined in the mouse, rat, dog and monkey. Target organ for indoprofen toxicity is the gastrointestinal tract (ulcerogenic effect). In vitro and in vivo studies of mutagenicity did not show any mutagenic activity. No embryotoxic or teratogenic effect was noted in reproduction toxicity studies in rats, rabbits and monkeys.

Animals↗

PubMed1980

Glipizide and hepatic glycogenolysis.

Glipizide, a new sulfonylurea recently introduced for the treatment of diabetes, was studied to check its possible extrapancreatic effects. Rats were given a subcutaneous injection of 1 g/kg glucosamine: this dose caused marked hyperglycemia and a decrease in hepatic glycogen, but does not alter blood insulin levels. Pretreatment with i.v. dose of 37.5 microgram/kg glipizide 1 hour before the glucosamine load, significantly inhibits the hyperglycemia and the decrease of hepatic glycogen. This dose of glipizide does not affect blood sugar levels, although it does induce a transient rise in insulin secretion, which lasts no more than 10 minutes after administration. Since glucosamine was administered 1 hour after the sulfonylurea by which time the interference of insulin was no longer felt, it may be concluded that in the experiment described, glipizide seems to have some other action apart from stimulating insulin secretion.

Adrenalectomy↗

PubMed1980

Effect of glipizide on muscle metabolism in vitro.

This paper contains the results of further investigation on the possible extrapancreatic activity of glipizide. An in vitro method, using isolated rat diaphragm was selected. Muscle uptake of C14 glucose and output of labelled CO2, were measured. Insulin was used as the reference substance. The results of our experiments indicate that there is a qualitative difference in the effects of the two experimental situations. However, from these findings it may be assumed that glipizide facilitates the uptake and metabolism of glucose in muscle, thus demonstrating an extrapancreatic effect, which contributes to the hypoglycemic activity of the drug.

Animals↗

PubMed1978