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Biomedical subjects

P Marchetti

Publications and source records attributed to P Marchetti.

At least 253 records · Page 14Linked to original sources
PubMed1981

Steroid-induced proteins in human endometrium.

The synthesis of soluble proteins in human endometria at various phases of menstrual cycle was evaluated by polyacrylamide gel electrophoresis of [35S]methionine-labeled proteins. Densitometric analysis of the gels revealed alterations in the rate of synthesis of single protein bands throughout the cycle. Administration of conjugated estrogens (Premarin) to women undergoing hysterectomy, or exposure, in vitro, of the endometrial tissue to 17 beta-estradiol produced an increased incorporation of [35S]methionine into a specific protein which migrated on SDS-polyacrylamide gels at a molecular weight of about 55 000. Induction of this protein was observed only in those endometria showing a secretory histological appearance. The protein was resolved into at least 2 different spots in two-dimensional gel electrophoresis. An increase in the rate of synthesis of another endometrial protein with an apparent molecular weight of 51 000 was observed in tissues exposed in vitro to medroxyprogesterone acetate. These steroid-induced proteins may be a useful marker for studying hormone action in both normal and neoplastic endometria.

Electrophoresis, Polyacrylamide Gel↗
PubMed1981

Glucocorticoid receptors and in vitro corticosensitivity of peanut-positive and peanut-negative human thymocyte subpopulations.

In 6 human thymus glands, the immature subset of thymocytes was separated from the more mature one, by differential peanut lectin agglutination. These 2 cell subpopulations were analyzed for glucocorticoid receptor content by using a whole cell assay, with (3H)-triamcinolone acetonide as tracer. The unagglutinated thymocytes (peanut negative) contained about 2 times more receptor sites per cell than agglutinated (peanut positive) ones (7650 +/- 1550 S.D. verus 3195 +/- 896 S.D.). The affinity for steroid was similar in both cell subsets, as was the stereospecificity for glucocorticoids, the time-course of steroid-receptor association, and cytoplasmic to nuclear translocation. Despite the greater number of glucocorticoid receptor sites, the peanut-negative thymocyte subpopulation did not differ from the peanut-positive one in its sensitivity to the inhibitory effects of triamcinolone acetonide, as determined by measurements of the incorporation of radiolabeled precursors of protein and DNA. Moreover, the peanut-negative subset appeared more resistant in vitro to the steroid-induced cell lysis as compared to the peanut-positive one. Thus, our data suggest that glucocorticoid receptor density and corticosensitivity are not directly correlated and that the number of glucocorticoid receptor sites may be dependent on the degree of immunologic maturation.

Binding Sites↗
PubMed1980

Induced versus pre-existing asymmetry models for the half-of-the-sites reactivity effect in bovine liver uridine diphosphoglucose dehydrogenase.

Half-of-the-sites reactivity of the catalytic site thiol groups of UDPglucose dehydrogenase (UDPglucose:NAD+ 6-oxidoreductase, EC 1.1.1.22) can be ascribed either to the induction of conformational asymmetry following derivatization of one half of the subunits or to intrinsic conformational differences in the subunits of the native enzyme. If the half-sites reactivity behavior is due to induction effects, the magnitude of the induction could be expected to depend on the nature of the covalent modification. On the other hand, if the half-sites reactivity behavior is due to pre-existing asymmetry and there is no communication between catalytic centers, the properties of unmodified sub-units should be independent of the nature of the covalent derivative introduced on the modified subunits. According to the induced asymmetry hypothesis, the catalytic activity of half-sites modified enzyme might be different for different covalent modifications, whereas for the rigid pre-existing asymmetry hypothesis the catalytic activity of half-sites modified enzyme should be the same regardless of the modifying group. During the course of catalytic site thiol group modification by a number of thiol specific reagents, the loss of enzyme activity was equivalent to the degree of modification for most of the reagents employed. However, with iodoacetate and 5-(iodoacetamidoethyl)aminonaphthalene-1-sulfonic acid, half-sites modification of UDPglucose dehydrogenase reduced catalytic activity by 58 and 78%, respectively, of the initial activity. These observations are consistent with a model in which there is communication between catalytic sites. Electron microscopy shows that the six subunits of UDPglucose dehydrogenase are arranged as a hexagonal planar ensemble.

Animals↗
PubMed1980

Prostacyclin effects on the blood pressure responses to norepinephrine in rats treated with aspirin or indomethacin.

The atherosclerotic condition is associated with a reduction of PGI2 synthesis; moreover, in the presence of elevated serum cholesterol levels, pressor responses to norepinephrine are potentiated. In order to verify if a complete inhibition of PGI2 production affects the vascular reactivity, it was assayed two cycloxygenase inhibitors (lysine acetylsalicylate and indomethacin) in rats. The two drugs significantly potentiated the blood pressure responses to norepinephrine, and completely inhibited PGI2-like substances production by arterial rings. The prostacyclin infusion (15 ng/kg/min, i.v.) completely reversed such potentiation, without any major modification in the basal blood pressure values. These results show that PGI2 production is responsible for vascular tone modulation and may partially explain the altered vascular reactivity in the atherosclerotic condition.

Animals↗
PubMed1978

Half-sites oxidation of bovine liver uridine diphosphate glucose dehydrogenase.

6,6-Dithiodinicotinate shows half-of-the-sites reactivity towards the six catalytic-site thiol groups of bovine liver UDP-glucose dehydrogenase. The reagent introduces three intrasubunit disulphide linkages between catalytic-site thiol groups and non-catalytic-site thiol groups and abrogates 60% of the catalytic activity of the hexameric enzyme; excess 2-mercaptoethanol rapidly restores full catalytic activity. These results show the half-of-the-sites behaviour of the enzyme with the reagent and the presence of a non-catalytic-site thiol group capable of forming a disulphide linkage with a catalytic-site thiol group on the same subunit without irreversible denaturation.

Binding Sites↗
PubMed1975

Studies on the positive inotropic effect of phenylephrine: a comparison with isoprenaline.

1. The effects of phenylephrine and isoprenaline on the isometric contraction of guinea-pig ventricle were compared over the whole range of their respective dose-response curves. 2. In preparations driven at 2.5 Hz the increase in contractile force induced by either isoprenaline of phenylephrine was linearly correlated to an increase in maximum velocity of force development. The relaxation time was shortened by isoprenaline but not by phenylephrine. 3. The negative inotropic effect induced by delta [N-(3,4-dimethoxyphenethyl)-N-methyl-amino]-alpha-(3,4,5-trimethoxyphenyl)alpha-isopropylvaleronitrile hydrochloride (D(600)) was reversed by isoprenaline, but little influenced by phenylephrine. 4. The study of the interval-force relationship shows that the increase in contractile force induced by phenylephrine (3 X 10(-5) M) was relatively greater at low frequencies of stimulation, and that the maximum effect was reached at the frequency of 1 Hz. 5. The positive inotropic effect of phenylephrine (10-4 M) was significantly higher at a frequency of 1 Hz than at 2.5 Hz; the effect of isoprenaline (3 x 10-8 M) was not significantly different at the two driving frequencies. 6. In preparations driven at 1 Hz the inotropic effect of the lower concentrations of phenylephrine was due to an increase in the time to peak tension without any change of the maximum velocity of force development; however an increase of this parameter became evident only after higher concentrations of the amine (10-5 M or more), associated with a progressive shortening of the time to peak. 7. A correlation between mechanical and electrophysiological effects of phenylephrine is attempted; the suggestion is advanced that the prolongation of the action potential and of the active state duration may be an important factor in the inotropic effect of phenylephrine.

Action Potentials↗
PubMedDate not supplied

Effects of prolonged exposure to pancreatic glucagon on the function, antigenicity and survival of isolated human islets.

BACKGROUND: Certain clinical conditions are associated with inappropriately high levels of circulating glucagon. To date, little information is available about the direct effects of prolonged exposure of human islet cells to pancreatic glucagon. In the present study we evaluated the function, antigenicity and survival of human islets exposed for 24 h to human pancreatic glucagon. METHODS: We prepared human islets of Langerhans by collagenase digestion and density-gradient purification, incubated them for 24 h with 44 or 430 pmol/l pancreatic glucagon at physiological (5.5 mmol/l) glucose level, and evaluated their insulin release function, which was then compared with that obtained from islets kept at high (11.1 mmol/l) glucose concentration. In addition, aliquots of the islets were evaluated to assess their chemotactic properties towards human monocyte-macrophage cells, and their potency to induce cytokine release from human lymphocytes. Finally, survival of the islet cells cultured under varying conditions was evaluated, and an assessment was performed of mRNA expression of Bcl-2 and Bax proteins. RESULTS: The insulin secretion results demonstrated that, compared to the control islets, the islets previously exposed to either 44 or 430 pmol/l glucagon exhibited changes in insulin release in response to glucose, consisting of augmented secretion at low glucose challenge, and no further significant increase at high glucose stimulation, similar to the effects observed with islets pre-cultured with high glucose. These effects were reversible, as documented by the recovery of normal islet sensitivity to glucose after an additional 24-h culture in medium lacking glucagon. Compared to control islets, the culture medium from islets pre-cultured with high glucagon or high glucose showed an increased chemotactic potency towards human monocyte-macrophage cells. In addition, human lymphocytes released a greater amount of tumour necrosis factor alpha when co-cultured with the islets pre-exposed to high glucagon or high glucose, whereas no significant difference was observed (in comparison with control islets) as regards the release of gamma-interferon, interleukin-2 and interleukin-10. The TUNEL technique and RT-PCR showed, respectively, no major difference in cell survival and expression of mRNA encoding for Bcl-2 and Bax protein between control islets and islets kept for 24 h in the presence of high glucagon or high glucose. CONCLUSIONS: Our results show that in vitro exposure of human islets to pancreatic glucagon for 24 h causes changes in the function and antigenicity of isolated human islets that are similar to the changes observed after pre-culture with increased glucose levels. Under our experimental conditions, these changes were not accompanied by any evidence of cytotoxicity.

Cell Survival↗
PubMedDate not supplied

Effect of plasma metformin concentrations on serum lipid levels in type II diabetic patients.

In this study we evaluated the relationships between plasma metformin levels, measured by reverse-phase high-performance liquid chromatography, and serum lipid levels in 20 metformin-treated, type II diabetic patients. Mean fasting plasma metformin concentration was 490 +/- 188 ng/ml. No correlation was found between daily dose of drug and lipid parameters. A significant correlation emerged between circulating metformin concentration and serum triglycerides (r = -0.574, p less than 0.01), HDL-cholesterol (r = 0.583, p less than 0.01) and HDL2-cholesterol (r = 0.670, p less than 0.05). Multiple linear regression analysis showed that the correlation between plasma metformin concentration and serum triglycerides still remained significant after correction for other clinical and metabolic parameters. Total cholesterol and HDL3-cholesterol were not correlated with metformin concentrations. These results demonstrate the clinical usefulness of measuring plasma metformin concentrations and indicate that some effects of metformin on lipid metabolism depend on the drug plasma levels.

Aged↗
PubMedDate not supplied

Low dose metformin in the treatment of type II non-insulin-dependent diabetes: clinical and metabolic evaluations.

Low doses of metformin (500 mg twice daily) were administered to 20 diabetic patients, combined with the original sulfonylurea treatment which had become ineffective even at full dosage. After 1 and 5 weeks, the effects of the drug on glycemic control, blood intermediate metabolites and monocyte insulin receptors were monitored. Metformin clearly improved glycemic control by reducing both fasting blood glucose from 189.88 +/- 21.11 mg/dl to 131.12 +/- 16.02 mg/dl after 1 week and to 130.11 +/- 13.29 mg/dl after 5 weeks (p less than 0.025 both after 1 and 5 weeks); the diurnal blood glucose average fell from 235.33 +/- 24.11 mg/dl to 174.66 +/- 23.45 mg/dl (p less than 0.0025) after 1 week and to 177.65 +/- 21.71 mg/dl (p less than 0.0005) after 5 weeks. Consequently both blood glycosylated hemoglobin (p = n.s. after 1 week, p less than 0.025 after 5 weeks) and serum fructosamine (p less than 0.0025 after both 1 and 5 weeks) also decreased after metformin treatment. No change in plasma insulin and C-peptide levels was reported and no modification in diurnal rhythms of blood lactate, pyruvate, alanine glycerol and beta-OH-butyrate was detected at any time during metformin treatment. All the changes documented in the binding values were already complete at the end of the first week; insulin binding to monocytes increased slightly but significantly (p less than 0.05) and the number of receptors per cell rose (p less than 0.05) but could not be correlated to any index of glycemic control. These data suggest that the antidiabetic action of metformin is neither related to its lactate-increasing activity nor does it depend upon its inducing an increase in insulin binding values. This metformin-related hypoglycemic effect might be the result, at least in part, of a reduced oxidative phosphorylation without inhibition of hepatic gluconeogenesis and/or of decreased hepatic glucose output. Moreover, our data are also consistent with the hypothesis that metformin might affect insulin action at a post-receptor level.

3-Hydroxybutyric Acid↗