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Biomedical subjects

F Zonta

Publications and source records attributed to F Zonta.

At least 37 records · Page 2Linked to original sources
PubMed1987

Determination of dissociation constants and relative efficacies of some potent muscarinic agonists at postjunctional muscarinic receptors.

This study was undertaken to determine dissociation constants (KA and relative efficacies (er) of seven muscarinic agonists (methylfurtrethonium; dioxolane, oxathiolane, carbachol, muscarine, muscarone and oxotremorine) in three isolated tissues (guinea-pig ileum and atria and rat urinary bladder). The rank order of affinities (-log KA) of the various compounds varied depending on the tissue used. er values for the different agonists did not differ significantly from each other in any of the three tissues, except that the er of muscarine in the guinea-pig ileum was higher than those of the other compounds and that of oxotremorine in the rat urinary bladder was lower than those of the other agonists. Comparisons among tissues show that KA and er values were the same in different tissues for some compounds (muscarone, muscarine and methylfurtrethonium), while significant differences were found for the other compounds. This suggests the existence of a discrete receptor population recognized by some but not all agonists. For oxotremorine er as well as -log KA, is greater in atria than in smooth muscle: these factors combine to determine the cardioselectivity of this compound which can now ascribed to receptor selectivity.

Animals↗
PubMed1986

Comparative studies of the postjunctional activities of some very potent muscarinic agonists.

This study was undertaken to determine the potencies of seven muscarinic agonists (methylfurtrethonium, dioxolane, oxathiolane, carbachol, muscarine, muscarone and oxotremorine) on the postjunctional muscarinic receptors of seven isolated preparations (guinea pig taenia-coli, ileum, jejunum, trachea and atria and rat jejunum and urinary bladder). The results indicate that the rank order of sensitivity of the preparations varies independently of the potency of the agonist used and it is almost the same for all the compounds with the exception of oxotremorine. Muscarone was the most potent compound in all the tissues. Intergroup comparisons in each preparation and the evaluation of the equieffective molar ratios relative to muscarone revealed that carbachol possesses a certain degree of cardioselectivity and oxathiolane, on the other hand, is much less active on the cardiac tissue than on the others. Oxotremorine is a peculiar compound endowed with cardioselectivity.

Animals↗
PubMed1986

The influence of verapamil and papaverine on the calcium- and epinephrine-induced responses of isolated guinea-pig atria.

The effects of papaverine and verapamil on Ca2+ - and epinephrine evoked responses were investigated on spontaneously beating atria of the guinea-pig. Papaverine showed a non competitive antagonism against epinephrine but was ineffective against Ca2+; verapamil antagonized both the action of epinephrine and Ca2+ in a different manner but at the same concentrations. The pharmacological prerequisite to classify an anti-Ca2+ substance as a blocker of Ca2+ entry (that is the ability to selectively antagonize the Ca2+ -induced contraction relative to those of norepinephrine in vascular smooth muscle) was not met by the results obtained in the cardiac tissue. The behaviors of verapamil and papaverine with regard to Ca2+ response suggest another criterion for classifying a substance as a Ca2+ entry blocker based on the ability or inability to inhibit the response of the atrial preparation to Ca2+.

Animals↗
PubMed1985

Quantitative analysis of phylloquinone (vitamin K1) in soy bean oils by high-performance liquid chromatography.

A high-performance liquid chromatographic method for determining phylloquinone (vitamin K1) in soy bean oils is described. Resolution of vitamin K1 from interfering peaks of the matrix was obtained after enzymatic digestion, extraction and liquid-solid chromatography on alumina. An isocratic reversed-phase chromatography with UV detection was used in the final stage. The quantitation was carried out by the standard addition method, and the recovery of the whole procedure was 88.2%.

Chromatography, High Pressure Liquid↗
PubMed1984

Quantitative high-performance liquid chromatographic method for determining the isomer distribution of retinol (vitamin A1) and 3-dehydroretinol (vitamin A2) in fish oils.

Seven retinol and seven 3-dehydroretinol geometric isomers were simultaneously fractionated on a silica column using a ternary mobile phase (2-propanol-1-octanol-n-hexane, 0.2:3.8:96). The method was applied to determine vitamin A active compounds present in fish oils. The standard additions method was used to obtain the recovery of the analytes, which was found to be the same for vitamin A1 and A2 (89%). Correction factors for determining all isomers when the peak areas are integrated at 326 nm are reported, so that the quantitative determination may be reproduced by others using the proposed method, which allows all data to be referred to the calibration graph of all-trans-retinol only. As every isomer is quantified separately, the method also permits the determination of the real vitamin A biopotency of the samples.

Animals↗
PubMed1984

High-performance liquid chromatography of retinals, retinols (vitamin A1) and their dehydro homologues (vitamin A2): improvements in resolution and spectroscopic characterization of the stereoisomers.

A study of mobile phases for the improved high-performance liquid chromatographic resolution of retinal, 3-dehydroretinal, retinol and 3-dehydroretinol stereoisomers is described. By using 1-octanol as a phase modifier in n-hexane, the simultaneous separation of a complex mixture of vitamin A1 and A2 isomers was satisfactorily achieved, while the separation of the corresponding aldehydes required a ternary mixture of 2-propanol, dioxane and n-hexane. All peaks were spectroscopically characterized by recording their UV spectra, which are reported together with comparative tables of the absorbance maxima of the stereoisomers.

Alcohols↗
PubMed1984

High-performance liquid chromatography of the unsaponifiable from samples of marine and freshwater fish: fractionation and identification of retinol (vitamin A1) and dehydroretinol (vitamin A2) isomers.

Retinol (vitamin A1) and dehydroretinol (vitamin A2) geometric isomers, obtained in photosynthetic mixtures or from natural samples, were simultaneously fractionated by means of isocratic normal phase high-performance liquid chromatography. The use of low percentages of isopropanol (0.4-1.1%) as a modifier in hexane was studied, and the resolution of both pairs of retinols (9-cis/all-trans and 13-cis/11-cis) whose baseline separation had not previously been achieved was obtained. The proposed chromatographic method therefore allows the complete separation of all six of the most commonly occurring retinols in natural samples, including the above four mono cis- retinols plus the two 9,13- and 11,13-di-cis- retinols . Photoisomerization of retinal and of retinol in different solvent systems and during the extraction process was also studied, before analyzing the unsaponifiable from fresh and marine water fish, which constitute rich natural sources of both vitamins A1 and A2. Vitamin A2 was found to be present in different relative percentages depending on the analytical matrix. Four cis isomers (9-cis-, 11-cis-, 13-cis- and 9,13-di-cis-retinol or corresponding dehydroretinols ) were found to occur naturally together with the main all-trans form, confirming the need to separate geometric isomers in every dosage of vitamin A-containing compounds.

Animals↗
PubMed1984

Inhibition of norepinephrine- and 5-hydroxytryptamine-induced contraction on rat aorta by dihydroergocristine.

Norepinephrine (NE), 5-hydroxytryptamine (5-HT) and tyramine (Tyr) elicited concentration-related contractile responses on rat aorta strips. The maximum contractile responses evoked by 5-HT and NE were comparable; on the contrary the maximum response induced by Tyr was only 50% that of NE. Pretreatment with reserpine failed to modify the concentration-response curve for both Tyr and 5-HT. 5-HT concentration-response curves antagonized competitively by methysergide, 5-HT may be assumed to act directly on 5-HT receptors. The concentration-response curve for NE was shifted to the right by dihydroergocristine (DHEC) and, at least in a certain dose range, the observed agonist-antagonist interaction fulfilled the condition for competitive antagonism. With higher doses a decrease of the maximum response was obtained. DHEC antagonized 5-HT in a non competitive manner, shifting to the right and flattening the dose-response curves of this agonist. The doses needed to obtain such anti-5-HT effect are not too far from those giving alpha-adrenolytic effects.

Animals↗
PubMed1984

Mechanism of smooth muscle relaxation by rociverine.

Experiments were carried out in vitro on a new antispasmodic drug, 2-(diethylamino)-1-methylethyl-cis-1-hydroxy[bicyclohexyl] -2-carboxylate (rociverine), to elucidate further the mechanism of its smooth-muscle relaxation. On the furtrethonium contractions of rat jejunum rociverine exerts both a competitive antagonism, about 3000 times less than that of atropine, and a noncompetitive antagonism equal to that of papaverine. Both on rat vas deferens and on rabbit aorta rociverine at low doses slightly potentiates the response to norepinephrine (unrelated to any inhibition of uptakes), whereas at higher doses it depresses the maximum effect, 10 times more on the vas deferens than on the aorta. Against calcium in the same preparations rociverine behaves as a competitive antagonist with 10 times less potency than verapamil on the vas deferens and 300 times less on the aorta. In negative inotropic and chronotropic action on guinea-pig atria rociverine is 300 and 100 times, respectively, less potent than verapamil and in negative inotropic action on KCl-depolarized guinea-pig ventricular strips, whose contractility is restored by histamine, it is 70 times less potent than verapamil. In sum, the smooth-muscle relaxant action of rociverine depends on a modest antimuscarinic action and a direct myolytic action, the latter probably being due to an inhibitory action on the transmembrane fluxes of Ca2+. The potency ratio relative to verapamil indicates that the anti-Ca2+ action of rociverine is greater on the visceral smooth muscle than on cardiac and vascular muscle.

Animals↗
PubMed1984

The 5-atom rule and the subclassification of peripheral postsynaptic muscarinic receptors.

The effects of five pairs of muscarinic compounds in homology relationship within each pair on peripheral postsynaptic muscarinic receptors of rat jejunum and guinea-pig atria and trachea were studied. The relative activities within each pair of compounds were similar for all the biological responses studied. It is reasoned that, at least in the tissues examined, the resemblance between the agonist receptors must be very close.

Acetylcholine↗
PubMed1983

High-performance liquid chromatography of fat-soluble vitamins. Simultaneous quantitative analysis of vitamins D2, D3 and E. Study of percentage recoveries of vitamins from cod liver oil.

Vitamins D2, D3 and E were resolved and quantified by applying reversed-phase high-performance liquid chromatography to extracts of cod liver oil. The method, using two reversed-phase C18 columns and a ternary mixture of acetonitrile, methanol and water as the eluent resolved all fat-soluble vitamins well, including the pair D2-D3. The extraction procedure was studied; the recoveries, using two different solvents (hexane and diethyl ether) for extractions were 60.6 +/- 1.0 and 77.1 +/- 1.1, 56.9 +/- 1.2 and 74.8 +/- 0.8, and 14.1 +/- 0.7 and 89.8 +/- 1.4% for vitamins D2, D3 and E, respectively.

Cholecalciferol↗
PubMed1983

Action of papaverine and verapamil on norepinephrine and calcium evoked contraction of vascular and non vascular smooth muscle.

On isolated rat vas deferens both papaverine and verapamil show a non competitive antagonism against norepinephrine and a competitive antagonism against Ca2+. Verapamil is nearly 100 times more active than papaverine. On the main pulmonary artery and on the thoracic aorta of the rabbit, verapamil shows a competitive antagonism against both norepinephrine and Ca2+ but it is more effective (almost 100 times) against Ca2+ than norepinephrine. Papaverine also shows a competitive antagonism against norepinephrine but a non competitive antagonism against Ca2+. The contrasting results obtained on rat vas deferens and rabbit vessels might be due to: 1) mechanism(s) of action of the agonist; 2) properties of the biological object as far concerns receptor activation and mechanism(s) of excitation-contraction coupling; 3) mechanism(s) of action of spasmolytic drugs. All these factors act in a cooperative way in determining the quality and the quantity of the observed responses.

Animals↗
PubMed1983

Synthesis and biological activity of heterocyclic acyl-cholines.

Five new heterocyclic acyl-cholines were synthetized through 1,3-dipolar cycloaddition and their adrenergic, cholinergic and histaminergic activity evaluated. The tested compounds did not show any significant activity; some of them, in particular the isoxazole derivative (X), shift the dose-response curve of norepinephrine to the left.

Animals↗
PubMed1983

Action of cocaine on norepinephrine- and calcium-induced contraction of vascular smooth muscle.

The action of cocaine on the norepinephrine- and calcium-induced contraction of the thoracic aorta and the main pulmonary artery of the rabbit was studied. Cocaine, depending on the employed concentrations, shows a competitive or a non-competitive antagonism against norepinephrine, while, against calcium, cocaine, at the used concentrations, shows a competitive antagonism. The results are discussed in the light of literature data obtained from different preparations of several animal species. It is clear that the actions of local anesthetics must be evaluated through a wide range of doses and by considering the properties of the biological object.

Animals↗
PubMed1982

High-performance liquid chromatography of fat-soluble vitamins: separation and identification of vitamins D2 and D3 and their isomers in food samples in the presence of vitamin A, vitamin E and carotene.

Vitamins D2 and D3 and their corresponding previtamins and provitamins were resolved by reversed-phase high-performance liquid chromatography using a ternary solvent system (acetonitrile-methanol-water) pumped according to a gradient elution programme. The D vitamins were also resolved in the presence of other lipid-soluble vitamins (A, E and K1) and carotene. The peaks were monitored with a UV-visible variable-wavelength detector and were detected at their maximum absorbance, resulting in maximum sensitivity. Lipid-soluble vitamins and carotene were resolved in extracts obtained from oils and butter, thus permitting their identification in a single chromatographic run.

Butter↗
PubMed1981

Actions and interactions of ergotamine and dihydroergocristine in rat aortic strips.

The stimulating actions of ergotamine and serotonin were compared with that of noradrenaline on the rat isolated aorta. The results are discussed in the light of those obtained on other vascular preparations. On ergotamine or noradrenaline contracted aortic strips the antagonist activity of dihydroergocristine in comparison with that of papaverine was studied. Both agents were able to induce dose-dependent relaxations.

Animals↗
PubMed1980

[Study of maximal response of the rat vas deferens. I - study of adrenergic amines with diverse mechanisms of action and the influence of cast concentration in the physiological solution].

As a preliminary to research on phenomena connected with the appearance of maximal responses in the isolated rat vas deferens greater than those obtainable with noradrenaline, the responses to noradrenaline, octopamine and thyramine under various experimental conditions are discussed. Octopamine give maximal responses which are consistently greater than those with noradrenaline but the differences are scarcely significant. Variation of the Ca2+ concentration in the physiological solution affects response to the three amines in a different way. It appears that when there is an indirect component in the mechanism of action, lack of Ca2+ has less effect on the activity of the compound.

Animals↗