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Biomedical subjects

A De Santis

Publications and source records attributed to A De Santis.

At least 91 records · Page 5Linked to original sources
PubMed1986

Inhibition of adenylate cyclase by transglutaminase-catalyzed reactions in pigeon erythrocyte ghosts.

We report the occurrence in pigeon erythrocytes of a soluble Ca2+-dependent transglutaminase (TGase) activity. The effect of the erythrocyte ghost protein modifications, determined by TGase-catalyzed reactions, on adenylate cyclase, phospholipid methyltransferase I and II activities and on the lipidic matrix fluidity of the membrane was investigated by using a purified guinea pig liver TGase preparation. The results showed a significant inhibitory effect of such modifications both on the basal and on the variously stimulated (by NaF, Gpp(NH)p alone or in the presence of 1-isoproterenol) adenylate cyclase activity. By contrast, both the phospholipid methylation and the fluidity of the lipidic matrix of the membrane were unaffected by TGase-mediated reactions. These data suggest a new possible inhibitory mechanism of the cyclic AMP synthesis which might be triggered by the enhancement of the cytosolic Ca2+ concentration.

Adenosine Triphosphate↗
PubMed1986

Myelin basic protein ability to organize lipid bilayers: structural transition in bilayers of lysophosphatidylcholine micelles.

Myelin basic protein isolated by a single step with the cationic detergent cethyltrimethylammonium bromide in a lipid-bound form is able to induce structural transition of lysophosphatydilcholine micelles into multi-laminar vesicles. This finding, observed through electron microscopy, is discussed in the light of the assumed ability of the basic protein to organize myelin lipids.

Animals↗
PubMed1986

Biliary secretion of phosphatidylcholine and its molecular species in cholecystectomized T-tube patients: effects of bile acid hydrophilicity.

The aim of the present study was to establish whether the oral administration of bile acids with different hydrophilic properties affects the amount of phosphatidylcholine as well as the pattern of PC molecular species secreted in bile. We studied the biliary output of total and individual PC species in cholecystectomized T-tube patients, with a total biliary outflow, after oral administration of 750 mg of ursodeoxycholate (3 patients) or deoxycholate (3 patients). The latter experiments were repeated after 3 days of taurine supplementation (1500 mg daily) in order to increase, by means of the tauro-conjugation, the hydrophilicity of the secreted BA. A linear function was observed, during all the studies, between BA and PC biliary secretion, but the amount of PC secreted per mole of BA was higher for the less hydrophilic BA, such as deoxycholate, than for the more hydrophilic ursodeoxycholate or during deoxycholate plus taurine experiments. With regard to the pattern of PC molecular species, we observed no changes after administration of ursodeoxycholate. An increase in the secretion of the major polyenoic species (i.e., 16:0-18:2 and 16:0-20:4), with respect to the secretion of the monoenoic, was revealed during deoxycholate experiments. Conversely, during the deoxycholate plus taurine experiments, the secretion of the major monoenoic PC species (i.e., 16:0-18:1) increased more than that of the polyenoic species. We suggest that the observed modifications of the pattern of PC molecular species, secreted in bile, represent the result of a physicochemical effect of BA on liver membranes.

Bile↗
PubMed1986

Sperm maturation in human semen: role of transglutaminase-mediated reactions.

A Ca2+-dependent, transglutaminase-like activity has been detected both free in the human seminal plasma and bound on the spermatozoon surface. A marked variability of the two enzymatic activities in the semen of different normal subjects was observed; but limited changes occurred in various ejaculates of the same individual. Moreover, we report evidence of the ability of several seminal plasma proteins to act as acyl donor substrates for endogenous transglutaminase, whereas human ejaculated spermatozoa have been shown to possess polyamine-binding sites specifically involved in transglutaminase-catalyzed reactions. It is postulated that semen transglutaminase may play a role in suppressing sperm antigenicity and in the male gamete's acquiring biological features of a fully differentiated and fertile cell.

Adult↗
PubMed1986

Acute cholangitis: diagnostic and therapeutic problems.

A retrospective study was carried out, analyzing the diagnostic and therapeutic problems in 80 patients with acute cholangitis at the time of hospitalization. 23% of the 17 patients with pus in the bile duct showed Reynolds' pentad, which was observed in 10% of patients with nonsuppurative acute cholangitis. Common bile duct lithiasis was responsible in 80% of cases presenting with Reynolds' pentad and in 66% of postoperative mortality. In 75% of patients with tumors, the clinical picture showed a rapid development following PTC. 79% of patients responded positively to antibiotic therapy with subsequent elective surgery, while in 21% of patients who did not respond to antibiotic therapy, biliary drainage was the treatment of choice. Mortality in patients with shock or hypotension was 30% while it was 17% in those undergoing early (less than 72 hours) surgery. On the basis of the results, it is concluded that, since it is not possible to assess preoperatively whether a patient belongs to the group of suppurative acute cholangitis or to that of nonsuppurative acute cholangitis, the different severity of the clinical picture should be based on clinical and biochemical parameters. The most severe developments were observed in common bile duct lithiasis or in patients with tumors who underwent PTC. In case of failure to respond to antibiotic therapy, decompression was shown to be the most suitable treatment. The mortality rate is related to the severity of the clinical picture (presence or not of shock) as well as to a prompt surgical treatment.

Acute Disease↗
PubMed1985

On the binding of brain myelin basic protein to chromatographic resins.

Myelin basic protein, only in association with certain detergents, is able to bind irreversibly to the usual gel filtration media. While this binding is greatly advantageous in purification of proteolipid (the other major myelin protein), the question arises of the uncommon, nonphysiological behaviour of the basic protein. A relationship between binding property and basic protein structure is suggested.

Animals↗
PubMed1984

Transglutaminase-mediated modifications of the rat sperm surface in vitro.

Two transglutaminase-mediated modifications of the rat epididymal spermatozoon surface were demonstrated in vitro. Transglutaminase was effective in promoting the binding of spermidine to the sperm. Moreover, the enzyme, by reacting with one of the major proteins secreted by the rat seminal vesicle epithelium, produced a modified form of the protein with a higher molecular weight and the capability of binding to the sperm cells. A specific physiological role for the enzyme, bringing about modifications of the rat sperm surface in the seminal fluid environment, is suggested.

Acyltransferases↗
PubMed1984

The oxidation of external NADH by an intermembrane electron transfer in mitochondria from the ubiquinone-deficient mutant E3-24 of Saccharomyces cerevisiae.

Cells of the E3-24 mutant of the strain D273-10B of Saccharomyces cerevisiae, grown in a fermentable substrate not showing catabolite repression of respiration (2% galactose), are able to respire, in spite of their ubiquinone deficiency in mitochondrial membranes. Mitochondria isolated from these mutant cells oxidize exogenous NADH through a pathway insensitive to antimycin A but inhibited by cyanide. Addition of methanolic solutions of ubiquinone homologs stimulates the oxidation rate and restores antimycin A sensitivity in both isolated mitochondria and whole cells. Mersalyl preincubation of isolated mitochondria inhibits both NADH oxidation and NADH-cytochrome c oxido-reductase activity (assayed in the presence of cyanide) with the same pattern. Electrons resulting from the oxidation of exogenous NADH reduce both cytochrome b5 and endogenous cytochrome c. The increase in ionic strength stimulates NADH oxidation, which is also coupled to the ATP synthesis with an ATP/O ratio similar to that obtained with ascorbate plus N,N,N',N'-tetramethyl-p-phenylendiamine (TMPD) as substrate. The effect of cyanide on these activities and on NADH-induced endogenous cytochrome c reduction is also comparable. These results support the existence in vivo and in isolated mitochondria of a energy-conserving pathway for the oxidation of cytoplasmatic NADH not related to the dehydrogenases of the inner membrane, the ubiquinone, and the b-c1 complex, but involving a cytochrome c shuttle between the NADH-cytochrome c reductase of the outer membrane and cytochrome oxidase in the inner membrane.

Electron Transport↗
PubMed1984

Cerebral polyamine metabolism: inhibition of spermidine biosynthesis by dicyclohexylamine.

Since a specific inhibition of cerebral spermidine (Spd) synthase activity by alicyclic amines was preliminarily observed in vitro, we examined the in vivo inhibitory effectiveness of dicyclohexylamine (DCHA) on Spd biosynthesis in 21-day-old rat brain. For this purpose a previously reported HPLC procedure (Porta et al., 1981a) was modified to analyze the cerebral levels of DCHA at the time of polyamine determinations. The intraperitoneally injected DCHA was shown to cross the blood-brain barrier easily, reaching high levels in the cerebral tissue (approximately 750 nmol/g brain) within 1 h of its administration. The effect of the drug on the polyamine metabolism resulted in a significant depletion of Spd biosynthesis from the sixth hour after the treatment and in an earlier and prolonged increase of the putrescine (Pt) steady-state levels. Conversely, the spermine (Spm) endogenous pools remained unchanged throughout the 24-h post-DCHA period. Moreover, following the intracerebral administration of [1,4-14C]Pt, significantly lower specific radioactivity (s.r.a.) values for labeled Pt and Spd were recorded in the brains of DCHA-treated animals. Conversely, after intracerebral [14C]Spd injection, the s.r.a. of newly formed [14C]Spm remained unchanged, confirming the specificity of the DCHA effect on the Spd biosynthesis.

Amines↗
PubMed1983

The extracranial portion of the pineal complex of the frog (frontal organ) is connected to the pineal, the hypothalamus, the brain stem and the retina.

The central connections of the frontal organ of the frog Rana esculenta were studied by means of the cobalt-filling technique using the cobaltic lysine complex. The results showed that the frontal organ has surprisingly more extended connections than those demonstrated after the application of other techniques. In fact, we found that it is connected to the pineal, the hypothalamus, the brain stem and the retina. These connections, which neuroanatomically have not been reported before, suggest that the frontal organ of the frog participates, in some way, in several different functions, such as neuroendocrine activities, motor responses and lateral eyes photoreception interaction.

Animals↗
PubMed1982

The reconstitution of oxidative phosphorylation in mitochondria isolated from a ubiquinone-deficient mutant of Saccharomyces cerevisiae.

Mitochondria, isolated from the ubiquinone-deficient nuclear mutant of Saccharomyces cerevisiae E3-24, are practically unable to oxidize exogenous substrates. Respiratory activity, coupled to ATP synthesis, can, however, be reconstituted by the simple addition of ethanolic solutions of ubiquinones. A minimal length of the isoprenoid side chain (greater than or equal to 3) was required for the restoration. Saturation of the reconstitution required a large amount of exogeneous ubiquinone, in excess over the normal content present in the mitochondria of the wild type strain. A similar pattern of reconstituted activities could be also obtained using sonicated inverted particles. Mitochondria and sonicated particles are also able to carry out a dye-mediated electron flow coupled to ATP synthesis in the absence of added ubiquinone, using ascorbate or succinate as electron donor. This demonstrates that the energy conserving mechanism at the third coupling site of the respiratory chain is fully independent of the presence of the large mobile pool of ubiquinone in the membrane.

Adenosine Triphosphate↗
PubMed1979

Effects of some divalent cations on synaptic transmission in frog spinal neurones.

1. Synaptic transmission between dorsal root afferents and motoneurones was studied in the isolated and hemisected spinal cord of frogs, using intracellular and extracellular recording techniques, and ionic substitutions of divalent cations in the bathing fluid. 2. Delayed components of excitatory post-synaptic potentials (e.p.s.p.s) evoked in motoneurones by dorsal root supramaximal stimuli, as well as the Ca2+-dependent slow after-hyperpolarization which follows antidromic spikes, were reversibly blocked by superfusing the cords with 'Ca2+-free' media containing Co2+ (4 mM) or Mg2+ (6-10 mM). However, short latency e.p.s.p.s persisted in these media for more than 8 hr. 3. The minimum synaptic delay of the Co2+ and Mg2+, resistant e.p.s.p.s, measured from the peak negativity of the extracellularly recorded presynaptic spike to the onset of the e.p.s.p., was 0.3 msec at 10 +/- 1 degrees C. 4. The Co2+, Mg2+-resistant e.p.s.p.s were graded, and could be elicited by stimulation of segmental or adjacent roots. Those evoked by each of two adjacent roots showed linear summation when the roots were stimulated simultaneously. 5. The Co2+, Mg2+-resistant e.p.s.p.s decreased in amplitude at stimulating frequencies between 10 and 100 Hz, and with paired stimuli at intervals shorter than 20-40 msec. These reductions in amplitude were paralleled by decreases in amplitude of the presynaptic population spike. 6. Solutions free of divalent ions, containing EGTA (2 mM) abolished the Co2+, Mg2+-resistant e.p.s.p.s. They remained blocked for a variable time after returning to Ca2+-free Ringer containing Mg2+ (8 mM). Their continued abolition at this stage is probably not due to changes in electrical properties of motoneuronal membranes. Eventually, the Mg2+-resistant e.p.s.p.s started recovering in the Ca2+-free Ringer containing Mg2+. The time of onset of this recovery depended on the duration of exposure to EGTA. 7. Sr2+ (2-11 mM), although less effective than Ca2+, restored the composite e.p.s.p.s evoked by dorsal root supramaximal stimuli, as well as the Ca2+-dependent slow after-hyperpolarization of the motoneurone. The composite e.p.s.p.s could not be restored with Ba2+ (2-10 mM). 8. The results suggest that the Co2+, Mg2+-resistant e.p.s.p is generated by electrical coupling between some afferent fibres (probably primary afferents) and motoneurones. The after-effects of EGTA treatments probably reflect uncoupling of electrotonic junctions. In contrast, the delayed components of the composite e.p.s.p.s are generated through chemical synapses whose divalent cation requirement is similar to that of the neuromuscular junction.

Action Potentials↗
PubMed1977

Effects of tilorone hydrochloride on cellular immunity (leukocyte inhibiting factor production from human lymphocyte stimulated by E. coli lipopolysaccharide).

Tilorone hydrochloride, a drug able selectively to affect T-lymphocyte fuction, when incorporated (at three different concentrations 0.1, 0.04, 0.02 microgram/ml) in lymphocyte culture, stimulated by 50 microgram/ml of E. coli LPS (026:B6 W), is able to abolish LIF production, due to endotoxin stimulation. Such effect is, may be, due to an impairment of T-cell activity, since tilorone at the same concentration decreases the number of ARFC and TRFC, which are specific markers for T-cells.

Escherichia coli↗
PubMed1977

Effect of some bacterial products on platelet electrophoretic mobility (PEM).

Bacterial LPS, used in our experiments, are able to decrease PEM at concentration of 100 microgram/ml after incubation with 1 X 10(7) platelets/ml for 30 min at 37 degrees C. Such effect is statistically significant for Bacteroides fragilis LPS, S. enteritidis and S. typhi. E. coli LPS 026:B6 W and E. coli 055:B5 W are not effective at all, S. minnesota (incomplete) LPS 595 and 345 free of 0-polysaccharide and partially lacking core in their molecule did not influence PEM, while S. minnesota LPS (S form) (a complete LPS) strongly decreased PEM. This fact could suggest that 0-polysaccharide is involved in this inhibitory effect on PEM. Klebsiella enterotoxin and B. cereus enterotoxin are able to decrease PEM at concentration of 100 microgram/ml, after incubation with 1 X 10(7) platelets for 30 min at 37 degrees C, while no inhibition of PEM was seen when Shighella enterotoxin and V. parahaemoliticus enterotoxin was used in similar way. The AA. conclude that endotoxin and enterotoxin are able to change the electrokinetic charge (negative) of platelets, thereby, causing a decrease of PEM.

Bacillus cereus↗