Protein composition in resting and activated platelets of type I diabetic patients

Protein composition of platelets of eleven type I diabetic patients and thirteen control subjects were analyzed by SDS polyacrylamide gel electrophoresis. Bands have been scanned and quantified. No significant difference was shown between controls and patients in any of the bands identified in electrophoretic patterns of whole platelet, membrane fraction, resting, activated and aggregated cytoskeleton. Data suggest that alterations observed in platelet function of diabetic patients cannot be connected to the changes in protein composition.

Clinical aspects of visceral pain

Pain producing stimuli in viscera are different from the stimuli which induce somatic pain. Two main clinical aspects of visceral pain are observed: true visceral pain and referred pain. The distinction among visceral pain, referred pain and somatic pain may be difficult in the so-called "intricate conditions". Furthermore, mnemonic traces may play an important role in determining clinical aspects of visceral pain.

The effects of noncollagenous matrix proteins on hydroxyapatite formation and proliferation in a collagen gel system

The effects of several noncollagenous matrix proteins on hydroxyapatite formation and growth were studied in a dynamic collagen gel system. In this system growth plate proteoglycan aggregates at concentrations of 1-10 micrograms/ml were effective inhibitors, desulfated aggregates from brachymorphic mice were less effective. Phosphophoryn at 1-100 micrograms/ml had no effect on formation; 60-120 micrograms/ml retarded mineral growth. Type X collagen at concentrations of 50-300 micrograms/ml had no effect on formation or growth.

Inhibition of the glycolytic pathway by methylglyoxal in human platelets

The incubation of human platelets with methylglyoxal and glucose produces a rapid transformation of the ketoaldehyde to D-lactate by the glyoxalase system and a partial reduction in GSH. Glucose utilization is affected at the level of the glycolytic pathway. No effect of the ketoaldehyde on glycogenolysis and glucose oxidation through the hexose monophosphate shunt was demonstrated. Phosphofructokinase, fructose 1,6 diphosphate (F1, 6DP) aldolase, glyceraldehyde 3-phosphate dehydrogenase and 3-phosphoglycerate mutase were mostly inhibited by methylglyoxal. A decrease in lactate and pyruvate formation and an accumulation of some glycolytic intermediates (fructose 1,6 diphosphate, dihydroxyacetone phosphate, 3-phosphoglycerate) was observed. Moreover methylglyoxal induced a fall in the metabolic ATP concentration. Since methylglyoxal is an intermediate of the glycolytic bypass system from dihydroxyacetone phosphate to D-lactate, it may be assumed that ketoaldehyde exerts a regulating effect on triose metabolism.

Alkaline extraction and reverse-phase high-performance liquid chromatography of adenine and pyridine nucleotides in human platelets

The levels of adenine (ATP, ADP, AMP) and pyridine (NAD, NADH) nucleotides in human platelets have been measured by a simple and reproducible method. A rapid alkaline extraction allows a complete recovery of the compounds concerned. The metabolic ATP and ADP in the cytosolic fraction, the amount released upon thrombin stimulation, and the ADP bound to F-actin have also been evaluated. Analysis was performed by reverse-phase, isocratic high-performance liquid chromatography on a 5-microns Lichrosorb RP-18 column with uv detection at 254 nm.

Platelet glucose metabolism in type I diabetic subjects

In a group of 35 type I diabetics, platelet glycolytic and glycogenolytic flux have been measured. In type I diabetic platelets glucose uptake was significantly reduced. The quite normal lactate production was obtained by a faster utilization of stored glycogen in these patients. Specific activity of glycolytic enzymes was normal, in particular the levels and kinetic properties of soluble and membrane bound hexokinase. The rate of glucose flux through the hexose monophosphate shunt, measured either in resting or in arachidonic acid-stimulated platelets, was normal in diabetics. Kinetics of glucose transport across plasma membrane have also been determined. Km was significantly increased in diabetic patients. No changes was shown in Vmax. Modifications present in membrane organization of patients could involve glucose transport protein.

Effect of diabetes mellitus on selected acid hydrolase activities in human platelets

Platelets were isolated from blood donated by 57 diabetic subjects, 41 insulin-dependent and 16 non insulin-dependent, ranging in age from 19 to 78 years, and by 54 healthy non-diabetic subjects ranging from 19 to 63 years of age. The platelets were ruptured by sonication and resultant preparations assayed for their levels of activity of seven acid glycohydrolases. Platelets from diabetic subjects contained only 50% of the alpha-L-fucosidase activity and about 60% of the acid phosphatase, beta-D-galactosidase, and beta-D-glucosidase activities of platelets from non-diabetic individuals; the differences were statistically significant. N-acetyl-beta-D-glucosaminidase activity in platelets from diabetic subjects was reduced by about 15% from normal levels while beta-D-glucuronidase and alpha-D-mannosidase activities were similar to those from non-diabetic individuals. A comparison of the data from older insulin-dependent diabetic and normal subjects with a similar age distribution yielded identical results for the two groups in all enzymes tested except fucosidase. Platelets of non insulin-dependent diabetics and those from non-diabetic subjects of a similar age distribution appear to possess similar levels of these acid hydrolases. There was no difference in levels of these platelet acid hydrolases between males and females in either the diabetic or non-diabetic group. Within the diabetic group, there was no difference in these platelet acid hydrolase activities between subjects with retinopathy and without retinopathy. There was no correlation of the enzyme activity levels of platelets from diabetic subjects with concentration of glycosylated haemoglobin, serum triglycerides or serum cholesterol.

Glucose transport across plasma membrane in human platelets

Studies have been carried out in the presence of 2-deoxyglucose, by utilizing a technique of platelet rapid filtration. Kinetic data suggest that glucose uptake across plasma membrane is the rate limiting step in its utilization. 2-deoxyglucose is transported by facilitated diffusion. L-glucose is transferred at only 1/1200 of the rate of glucose. Transport system shows high affinity for substrate. Transport is inhibited by cytochalasin B, phloretin and N-ethylmaleimide. Cytochalasin E does not affect 2-deoxyglucose uptake. Diamide can have activating or inhibitory effect. t-Butyl hydroperoxide is always activating. Insulin has no effect on rate transport. D-glucose, 3-O-methylglucose, non radioactive 2-deoxyglucose and D-mannose are strong competitors, whereas D-galactose and D-fructose compete weakly with 2-deoxyglucose transport.

Lactate overproduction in platelets of subjects affected with myeloproliferative disorders

In platelets of patients affected with myeloproliferative disorders, glycolytic and glycogenolytic flux have been examined. Results of studies on glucose uptake, glycogen breakdown and lactate formation have been reported. No difference in glucose uptake between controls and patients was observed, but in patients a higher lactate formation was always noted in the presence or absence of exogenous glucose, in correlation with a higher glycogen breakdown rate. Results could be explained by modified regulation mechanisms on glycogen phosphorylase.

Lysosomal enzymes in human platelets

In human freshly prepared platelets the following lysosomal enzymes were studied: alpha-mannosidase, alpha-fucosidase, beta-galactosidase, beta-glucosidase, beta-glucuronidase, beta-N-acetylglucosaminidase and acid phosphatase. For each of the examined enzymes the conditions providing maximal activity (pH, buffer), kinetic parameters (saturating substrate concentration and Km) as well as heat stability were established. On the basis of these parameters it is suggested that many of the serum glycohydrolases may be platelet derived.

Platelet glyoxalases in thrombocytosis

In platelets of patients suffering from thrombocytosis due to myeloproliferative disorders, glyoxalase I activity is significantly higher than in controls (P less than 0.01), while glyoxalase II levels are the same (P less than 0.3). The cellular concentration of glutathione is also increased in patients. Km values for methylglyoxal (glyoxalase I) and S-lactoylglutathione (glyoxalase II) are identical both in normal and pathological subjects, as are the thermostability of the two enzymes. The higher activity observed for glyoxalase I in patients could be related to a specific role of this enzyme in platelets.

Glucose and fructose utilization in human platelets. Effects of diamide

In this study we have reported that platelets metabolize fructose more slowly than glucose and probably by a different mechanism. While formed lactate is correlated with glucose utilized, in the presence of fructose an overproduction of lactate was demonstrated. The different behaviour of glucose and fructose was also shown by utilizing diamide at various concentrations. Low diamide concentrations increase glucose consumption, whereas higher concentrations inhibit. Fructose is gradually inhibited by increasing oxidant quantities. Data obtained suggests that diamide interferes with the transport process across platelet membrane. It is likely that glucose and fructose do not share the same transport mechanism. On the other hand only high diamide concentrations inhibit sugar metabolism by acting on the glycolytic flux at the level of some key enzymes.

Some aspects of platelet glucose metabolism in thrombocytosis due to myeloproliferative disorders

Some aspects of the glucose metabolism were investigated in platelets of 11 healthy donors and 11 patients suffering from thrombocytosis due to myeloproliferative disorders. Out of all the glycolytic compounds measured in resting platelets, dihydroxyacetonephosphate and fructose 1,6 bisphosphate were significantly higher in cells of subjects with thrombocytosis. No difference was observed in the basic net flux of glucose through the hexose monophosphate shunt. Addition of arachidonic acid to platelets of patients with thrombocytosis had a very poor effect in stimulation of the hexose monophosphate shunt, whereas high values of activation were obtained in control platelets. Lactate production determined by collagen was found significantly higher in all patients. These data observed in platelets of patients could be explained by a decreased pool of metabolic adenine nucleotides.

Platelet lysosomal enzymes are normal in myeloproliferative disorders

In platelets of subjects affected with myeloproliferative disorders the following lysosomal enzymes were studied: alpha-mannosidase, alpha-fucosidase, beta-galactosidase, beta-glucosidase, beta-glucuronidase, beta-N-acetylglucosaminidase and acid phosphatase. For each enzyme the specific activity, the optimum of pH and buffer, Km and saturating substrate concentrations, as well as thermostability were determined. Control and patient enzymes showed no difference.

Platelet membrane fatty acids in thrombocytosis due to myeloproliferative disorders

The fatty acid composition of platelet membranes has been analysed in patients with thrombocytosis due to myeloproliferative disorders, who had not taken any drugs. A significant increase in palmitic and oleic acid, together with a decrease in stearic, linoleic and arachidonic acids was observed. The fatty acid pattern of platelet membranes was also analysed in patients during treatment with ASA (acetylsalicylic acid). ASA ingestion completely normalizes the platelet content of palmitic acid and partially that of stearic and arachidonic acid, whereas it has no effect on the level of linoleic acid and raises that of oleic acid. The altered pattern of fatty acids observed in patients may interfere with platelet function by decreasing membrane fluidity. Treatment of patients with ASA seems to act on platelet membranes by partially normalizing the fatty acid composition.

The measurement of pain threshold in man by means of electrical stimuli. A critical appraisal

The problem of pain threshold measurement in man is critically considered. The advantages of electrical stimuli in determining the cutaneous pain threshold are discussed. The conducting properties of the skin to electric current are carefully examined: in fact, such properties must be taken into account when electrical stimuli are applied to the skin. A series of investigations on pain threshold measurement by means of electrical stimuli are reported. The different sensations induced by stimulating the skin with different kinds of electrodes and different types of stimuli were analysed: trains of 5 square waves of 0.5-2 msec at the frequency of 250 Hz, applied to the skin by means of unpolarizable electrodes, were selected as the best suited stimuli for practical application. This kind of stimulation was applied in physiological and clinical investigations. The measurement of pain threshold by electrical stimuli was especially useful for the clinical examination and for the study of pathogenetic mechanisms of painful diseases.

The effect of diamide and glutathione on the uptake of glucose by human erythrocytes

Diamide, directly added to human erythrocytes, inhibits glucose utilisation. The trend of this process is in good correlation with the intracellular concentration of GSH. Since diamide does not affect the glycolytic and hexose monophosphate-shunt-pathway enzymes, it is likely that the effect of diamide involves the sugar transport across erythrocyte membrane. Kinetic studies carried out on ghosts have shown that diamide decreases Vmax without affecting Km. GSH on the contrary stimulates glucose transport by increasing Vmax. The significance of GSH in the process of transport of sugar is discussed.

Changes of cutaneous sensory thresholds induced by non-painful transcutaneous electrical nerve stimulation in normal subjects and in subjects with chronic pain

Transcutaneous electrical nerve stimulation (TENS) of the nervi cutaneus surae medialis was applied to 59 healthy subjects and 30 patients suffering from chronic myofascial pain in one lower limb, with an intensity of current that induced a well tolerated tingling sensation. Each period of stimulation lasted 24 minutes. The thresholds of the tactile, tingling and painful sensations were tested at fixed intervals before, during and after stimulation. Trains of constant current square waves in the distribution area of the stimulated nerve (local thresholds) and in other areas (general thresholds) were used. In all subjects repeated changes of the current were necessary in order to maintain constant tingling during the first period of TENS (changing phase); after that few if any changes of the current were necessary (steady phase). There were changes in thresholds within the territory of the electrically stimulated nerve, and marked changes elsewhere and generally in the body. In healthy subjects local thresholds increased during both phases of TENS; general thresholds decreased during the changing phase and increased during the steady phase. After TENS, thresholds showed the same trend as during the steady phase. Trends of the sensory thresholds during and after TENS differed in different subjects according to their thresholds before TENS. Thresholds did not return to normal for more than 20 minutes after TENS. In the group of 30 patients there was a significant difference between thresholds on the two sides of the body. The difference between the two sides was reduced by TENS. Pain relief induced by TENS may be related to this fact.

Studies on the inactivation of glyceraldehyde-3-phosphate dehydrogenase by methylglyoxal

Glyceraldehyde-3-P dehydrogenase (E.C. 1.2.1.12) from rabbit muscle is rapidly inactivated by methylglyoxal following pseudo first-order kinetics. Substrate, as well as inorganic phosphate, affords protection, whereas NAD+ is ineffective. The arginine residue implicated in the reaction is probably the anion binding site of the phosphate group of the substrate.