Mumol Ml-1 Research Articles

Transport and metabolic pathway of thymocartin (TP4) in excised bovine nasal mucosa.

Thymocartin (TP4, Arg-Lys-Asp-Val) is the 32-35 fragment of the naturally occurring thymic factor (thymopoietin). Here studies on the nasal transport and metabolism of TP4 were performed. Freshly excised bovine nasal mucosa was taken as a model membrane. For permeation studies typical donor-receiver experiments (side-by-side) and finite-dose experiments with small volumes of highly concentrated solutions were carried out. The metabolic pathway of TP4 in nasal mucosa was found to occur according to a typical aminopeptidase cleavage pattern, stepwise forming Lys-Asp-Val and Asp-Val. TP4 metabolism experiments under reflection kinetics showed a saturation profile above 0.5 mumol mL-1. A non-linear kinetic model consisting of three steps in sequence was sufficient to describe the kinetics: for the first step saturable Michaelis-Meat kinetics, and for the second and the third step first-order kinetics were assured. The model was capable of simultaneously fitting the data for the full range of initial concentrations from 0.1 up to 1.0 mumol mL-1. Saturation kinetics was also found to be the prominent feature of the permeation experiments performed. In the lower concentration range (< 0.4 mumol mL-1), transport of TP4 across nasal mucosa was controlled by metabolism, in the higher concentration range (> 0.85 mumol mL-1) diffusion control became more important. We conclude that enhancement of absorption can be achieved when nasal aminopeptidases are saturated, e.g. at high TP4 concentrations.

The effect of hyperglycaemia on regional cerebral glucose oxidation in humans studied with [1-11C]-D-glucose.

The effect of hyperglycaemia on regional cerebral glucose utilization was studied in five healthy males fasted over-night using positron emission tomography. Selectively labelled glucose, [1-11C]-D-glucose, was used as a tracer. After correction for the small loss of [11C]CO2 from the tissue, this tracer measures the rate of glucose oxidation rather than the total rate of glucose metabolism. Each subject was investigated twice: during normoglycaemia (plasma glucose 5.3 +/- 0.3 mumol mL-1) and at the end of a 2-h period of hyperglycaemia (plasma glucose 13.8 +/- 0.7 mumol mL-1). Assuming unchanged rate constant for loss of labelled CO2 at normo- and hyperglycaemia the oxidative metabolic rate of glucose was found to be slightly larger at combined hyperglycaemia and hypersulinemia (0.30 +/- 0.01 mmol mL-1 min-1) than at normal glucose and insulin levels (0.25 +/- 0.01 mmol mL-1 min-1). This suggests that the process of glucose phosphorylation might not be fully saturated in the human brain or, alternatively, that the glycogen deposition increases during short-term hyperglycaemia. The relative increase of oxidative metabolic rate was considerably larger (approximately 50%) in white matter than in the brain as a whole (20%). The brain glucose content was found to increase non-linearly with increasing plasma glucose. Together with data from previous studies these results suggest that the free glucose in the human brain is close to zero when the plasma glucose is below 2 mumol mL-1.

Importance of nitric oxide in hepatic arterial blood flow and total hepatic blood volume regulation in pigs.

The importance of nitric oxide in regulating basal arterial blood flow has been examined in several different vascular beds by intra-arterial infusion of inhibitors of nitric oxide synthesis, but not in the arterial vascular bed of the liver. In the present study, N(G)-nitro-L-arginine (L-NNA), in a dose of 0.5 and 1.0 mumol mL-1 of hepatic arterial blood flow, was infused for 5 min into the hepatic artery in seven pigs anaesthetized with pentobarbital sodium. The haemodynamic effects observed by the first infusion were not further enhanced by the second infusion. Hepatic arterial resistance increased by 143 +/- 38% and hepatic arterial blood flow declined by 38 +/- 10%. A systemic effect due to 'spillover' was observed, as evidenced by an increase in mean aortic blood pressure of 24 +/- 4 mmHg. However, no significant increase in arterial mesenteric resistance was observed and total liver blood flow remained unchanged. Hepatic arterial vasodilation in response to occlusion of the portal vein, the arterial buffer response, remained intact after inhibition of nitric oxide synthesis. Liver lobe thickness, measured by an ultrasonic technique, was not found to change with inhibition of arterial nitric oxide synthesis, excluding a significant direct effect of arterial nitric oxide on liver capacitance. In conclusion, nitric oxide is an important regulator of hepatic arterial resistance, but does not mediate the hepatic arterial buffer response and was not found to play any significant role in total hepatic capacitance regulation.

Active surfactant in pharyngeal aspirates of term neonates: lipid biochemistry and surface tension function.

Alveolar surfactant is well known for its ability to reduce minimal surface tension at the alveolar air-liquid interface to values below 5 mN m-1. In addition, it has been suggested that surfactant is also present in the airways, particularly in the perinatal period. We isolated surfactant from pharyngeal aspirates obtained from 33 neonates immediately after delivery and analysed it for both phospholipid (PL) composition and surface tension function. PL classes and phosphatidylcholine (PC) molecular species were determined by normal and reversed-phase high-performance liquid chromatography (HPLC), respectively. Static and dynamic surface properties of the surfactant were studied in a pulsating bubble surfactometer. Sample volume was 1.3 +/- 0.5 mL (mean +/- SD) with a total amount of 2.5 +/- 1.3 mumol of PL and a concentration of 2.1 +/- 1.0 mumol mL-1 PL. HPLC analyses of PL classes revealed a composition identical with surfactant prepared from alveolar washes, i.e. PC 83.6 +/- 2.1%, sphingomyelin 1.4 +/- 0.5%, phosphatidylglycerol 8.1 +/- 1.6%, phosphatidylethanolamine 2.1 +/- 0.5% and phosphatidylinositol 2.6 +/- 1.1%. Thin-layer chromatography showed almost identical results but was more time-consuming and needed more material for analysis. Analysis of PC molecular species revealed a composition typical of human alveolar surfactant with 54.7 +/- 3.9% dipalmitoyl PC, 10.3 +/- 1.9% palmitoyloleoyl PC and 9.1 +/- 1.5% palmitoylmyristoyl PC. Minimal surface tension fell to values below 5 mNm-1 within 5 min of cycling in all subjects. The methods used in this study allowed for complete PL and surface tension analyses of surfactant obtained during routine pharyngeal suctioning after delivery at term. Whether they are also applicable to preterm neonates with respiratory distress remains to be determined.

One-pot enzymatic synthesis of the Gal alpha 1-->3Gal beta 1-->4GlcNAc sequence with in situ UDP-Gal regeneration.

The trisaccharide Gal alpha 1-->3Gal beta 1-->4GlcNAc beta 1-->O-(CH2)8COOCH3 was enzymatically synthesized, with in situ UDP-Gal regeneration. By combination in one pot of only four enzymes, namely, sucrose synthase, UDP-Glc 4'-epimerase, UDP-Gal:GlcNAc beta 4-galactosyltransferase and UDP-Gal:Gal beta 1-->4GlcNAc alpha 3-galactosyltransferase, Gal alpha 1-->3Gal beta 1-->4GlcNAc beta 1-->O-(CH2)8COOCH3 was formed in a 2.2 mumol ml-1 yield starting from the acceptor GlcNAc beta 1-->O-(CH2)8COOCH3. This is an efficient and convenient method for the synthesis of the Gal alpha 1-->3Gal beta 1-->4GlcNAc epitope which pays an important role in various biological and immunological processes.

Cerebral transport and metabolism of 1-11C-D-glucose during stepped hypoglycemia.

Attempts to measure blood-to-brain glucose transport and cerebral glucose metabolism with 11C-glucose have been hampered by methods that require jugular venous sampling or do not adequately account for the efflux of labeled metabolites from the brain. We performed eight positron emission tomography studies with 1-11C-D-glucose in macaques at arterial plasma glucose concentrations of 8.43 to 1.51 mumol ml-1 (152-27 mg dl-1) using a model that includes a fourth rate constant to account for regional egress of all 11C-metabolites. Values for blood-to-brain glucose influx, cerebral glucose metabolism, and brain free glucose concentration agreed closely with values obtained in mammals by other investigators. Values for net extraction fraction corresponded closely to simultaneously measured arteriovenous values. We demonstrated that utilization of a model that includes a fourth rate constant to account for regional egress of all 11C-metabolites with positron emission tomography and 1-11C-D-glucose provides accurate measurements of blood-to-brain glucose transport and cerebral glucose metabolism in vivo without need for jugular venous sampling, even under conditions of severe hypoglycemia.

Influence of incubated atracurium on rat liver function

Degradation of atracurium by Hofmann elimination and ester hydrolysis depends mainly on pH and temperature and is said to be independent of liver and kidney function. Consequently atracurium is used widely in patients with liver failure. However, there is evidence that incubation of atracurium at 37 degrees C and pH 8 leads to leakage of LDH from hepatocyte cell cultures. We have tested the hepatotoxic effects of incubated atracurium in an isolated perfused rat liver model. After equilibration, atracurium 2010 mumol ml-1 (preincubated at pH 8 and 37 degrees C for 120 min) was administered over a period of 10 min followed by perfusion of Krebs-Henseleit bicarbonate buffer for 60 min. We found that incubation resulted in considerable degradation of atracurium and formation of laudanosine. Administration of incubated atracurium did not produce either biochemical or morphological damage to liver cells, but caused considerable increase in bile flow. We conclude that administration of preincubated atracurium did not produce impairment of liver cell function. The increase in bile flow could be beneficial if it occurs clinically.

Lipoprotein lipase activity in patients with combined hyperlipidaemia

The aetiology of familial combined hyperlipidaemia remains obscure, with both genetic and environmental factors contributing to the phenotype, which is frequently associated with premature coronary heart disease. We have studied lipoprotein lipase (LPL) activity and hepatic lipase (HL) activity in patients with coronary heart disease to determine whether variation in lipase activities contributes to this phenotype. Forty-one patients (mean age 50 years; 30 male) were selected on the basis of cholesterol levels above 6.5 mmol/l and triglyceride levels above 2.2 mmol/l, with apoprotein B values over the 90th percentile. There was a family history of premature coronary heart disease in 78% and a personal history in 64%, at mean age 44, the patient group therefore predominantly corresponded to the common definition of familial combined hyperlipidaemia, appropriate in the absence of molecular markers. None of the patients was diabetic; hypertension and smoking were not over represented. Blood samples were taken following intravenous administration of heparin (100 IU/kg body wt), and LPL and HL activities were measured. Mean post-heparin LPL was significantly lower in patients than controls 10 min after heparin administration (2.98 +/- 1.04 and 3.86 +/- 0.93 mumol ml-1 h-1, respectively, P = 0.001), and 37% patients had values below the 10th percentile of controls. Both male and female patients had significantly higher HL activities than their respective controls at 5, 10, 20 and 30 minutes post-heparin. As expected, both female patients and controls had lower HL activities than males, although this sex difference did not reach statistical significance in the patient group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of free fatty acids found increased in women who develop pre-eclampsia on the ability of endothelial cells to produce prostacyclin, cGMP and inhibit platelet aggregation.

Recently, we showed that levels of circulating free fatty acids are increased in women who later develop pre-eclampsia long before the clinical onset of the disease. Among the serum free fatty acids, oleic-, linoleic-, and palmitic acid were found to be increased by 37, 25 and 25%, respectively. In the present study we asked if these free fatty acids can interfere with endothelial cell functions. Cultured endothelial cells were exposed to linoleic-, oleic- and palmitic acid in concentrations ranging from 0.016 to 0.133 mumol ml-1, resulting in molar ratios of free fatty acids to albumin of 0.2-1.6. We found that among these fatty acids, linoleic acid reduced the thrombin-stimulated prostacyclin release by 30-60%, oleic acid by 10-30%, whereas palmitic acid had no effect. Endothelial cells incubated in presence of linoleic acid showed a concentration-dependent reduction in prostacyclin release in response to thrombin, and cells incubated with linoleic acid for up to 28 h, showed a reduced thrombin-induced prostacyclin release at every time point. Endothelial level of cGMP mainly reflected the synthesis of endothelium-derived relaxing factor/nitrogen monoxide (EDRF/NO), since blocking of the endogenous production of EDRF/NO with N-omega-nitro-L-arginine, resulted in about 90% reduction in cGMP-content of the endothelial cells. Incubation with linoleic acid reduced the endothelial cGMP level by 70%. Linoleic acid reduced the endothelial cells ability to inhibit platelet aggregation by 10-45%, (p = 0.0019). It was concluded that linoleic acid impedes the ability of the endothelial cells to produce prostacyclin and cGMP, and to inhibit platelet aggregation.

Pharmacokinetics of varying doses of nicotinamide and tumour radiosensitisation with carbogen and nicotinamide: clinical considerations.

Plasma concentrations, after administration of varying doses of nicotinamide, were measured in CBA male mice using a newly-developed high performance liquid chromatography assay. In all dose groups, peak levels were observed within the first 15 min after an i.p. administration of 0.1, 0.2, 0.3 or 0.5 mg g-1 of nicotinamide. There was a clear dose-dependent increase in plasma concentration with increasing dose, with almost a five-fold lower concentration (1.0 vs 4.9 mumol ml-1) achieved with a dose of 0.1 mg g-1 compared with 0.5 mg g-1, respectively. The half-life of nicotinamide increased from 1.4 h to 2.2 h over the dose range (P < 0.01). Comparisons with previous pharmacokinetic data in humans show that clinically-relevant oral doses of 6 and 9 g in humans give plasma levels slightly higher than those achieved at 1 h with doses of 0.1 to 0.2 mg g-1 in mice. Tumour radiosensitisation with carbogen alone, and with carbogen combined with varying doses of nicotinamide (0.05 to 0.5 mg g-1), was investigated using a 10-fraction in 5 days X-ray schedule. Relative to air-breathing mice, a statistically significant increase in sensitisation was observed with both a local tumour control and with an in vivo/in vitro excision assay (P < or = 0.007). With the local control assay, a trend was observed towards lower enhancement ratios (ERs) with decreasing nicotinamide dose (from 1.85 to 1.55); carbogen alone was almost as effective as when combined with 0.1 mg g-1 of nicotinamide. With the excision assay, ERs for carbogen combined with nicotinamide increased with decreased levels of cell survival. At a surviving fraction of 0.02, enhancement ratios of 1.39-1.48 were obtained for carbogen plus 0.1 to 0.3 mg g-1 of nicotinamide. These were lower than those seen with the two higher doses of 0.4 to 0.5 mg g-1 (ERs = 1.63-1.69).

Effect on renin release of inhibiting renal nitric oxide synthesis in anaesthetized dogs

Nitric oxide plays an important role in the regulation of basal renal blood flow. This study was performed to examine whether selective inhibition of renal nitric oxide synthesis affects renin release in vivo. Accordingly, in six barbiturate-anaesthetized dogs renin release was examined before and after intrarenal infusion of the selective inhibitor of nitric oxide synthesis, NG-nitro-L-arginine (NOARG). NOARG was infused into the renal artery to yield a renal arterial blood concentration of 0.4 mumol ml-1. NOARG did not change systemic arterial blood pressure and glomerular filtration rate, but reduced basal renal blood flow by 26 +/- 2%. Urine flow, sodium and potassium excretion were reduced after inhibition of renal nitric oxide synthesis. Basal renin release (3 +/- 2 micrograms AI min-1) was not altered by NOARG infusion (1 +/- 1 micrograms AI min-1). To stimulate renin release the renal artery was constricted to a renal perfusion pressure of 50 mmHg. At this perfusion pressure infusion of NOARG reduced renin release significantly from 48 +/- 11 micrograms AI min-1 to 14 +/- 4 micrograms AI min-1. In conclusion, inhibition of renal nitric oxide synthesis reduces basal renal blood flow and reduces renin release stimulated by renal arterial constriction. These findings indicate that renal nitric oxide modulates both renal blood flow and renin release in vivo.

Nonlinear elimination and hepatic concentration of conjugation‐ metabolite of valproate in guinea‐pigs

The plasma clearance and metabolic rate characteristics of valproic acid (VPA) were studied using guinea-pigs placed on various (0.08-9 mumol ml-1 = 11-1303 micrograms ml-1) steady-state plasma concentrations (Css) by constant intravenous (i.v.) infusion. The total clearance (CL) was significantly decreased at plasma concentration of 0.61 mumol ml-1 (88 micrograms ml-1). The metabolic clearance of VPA was apparently biphasic. The maximum metabolic rate (Vmax) and the Michaelis-Menten constant (Km) for the primary (Vmax1, Km1) and the secondary (Vmax2, Km2) pathways were Vmax1 = 1.52 mumol min-1 kg-1, Km1 = 0.15 mumol ml-1, Vmax2 = 24.98 mumol min-1 kg-1 and Km2 = 11.70 mumol ml-1, respectively. The Km1 value was within clinical therapeutic concentration range. The formation of conjugated VPA (cjVPA) metabolite in liver was shown to be saturable. Plasma protein binding of VPA was also nonlinear. The dose-dependent decrease in metabolic clearance was counterbalanced by the increased unbound fraction (fu), resulting in a relatively constant apparent clearance of VPA over a wide concentration range. The hepatic concentration of VPA was not significantly different from the plasma unbound concentration, again over a wide concentration range. The biliary and hepatic concentrations of VPA were not significantly different; but the concentration ratio of cjVPA in bile compared with that of VPA in liver decreased against hepatic concentration of VPA, which suggests a saturable conjugation rate. The Km value estimated from hepatic cjVPA production as a function of plasma VPA concentration was comparable with the Km1 value.(ABSTRACT TRUNCATED AT 250 WORDS)

Follicular fluid composition in the grey seal (Halichoerus grypus) during the oestrous cycle.

During the period of lactational oestrus, the corpus luteum of ovaries of grey seals decreased in size following the birth of the pup, while on the contralateral ovary one major large follicle rapidly expanded. These large follicles had the highest concentration of oestradiol (4282 +/- 609 ng ml-1) and progesterone (499 +/- 168 ng ml-1). Osmolality (322 +/- 3 mosmol kg-1) and the intrafollicular concentration of electrolytes (Na: 126 +/- 1; Cl: 96 +/- 1; Ca: 1.3 +/- 0.1 mumol ml-1) and proteins (94 +/- 1 mg ml-1) were independent of stage of lactation and follicle size. Concentrations were lower in follicular fluid than in plasma. The concentrations of triglycerides and, to some extent, those of vitamin E, cholesterol and phospholipids were affected by the decrease in the plasma concentration of these components with the onset of lactation and the increase in follicle size. These two events resulted in a marked decrease of these components in the largest follicles at the end of lactational oestrus. Vitamin A (exclusively as retinol), although a blood-borne component in follicular fluid, was the only component with a higher concentration in small and medium follicles than in plasma and decreased with increasing follicle size despite an increase in plasma retinol. This decrease and the negative correlation with intrafollicular oestradiol might indicate a high demand of preovulatory follicle structures for vitamin A owing to its possible importance in steroid hormone or protein synthesis or in both processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphodiesterase inhibition in ventricular cardiomyocytes from guinea-pig hearts.

1. The present study compared the cyclic nucleotide phosphodiesterase (PDE) activities in cardiomyocytes and ventricular cardiac tissue from guinea-pigs. The aim of the study was to determine whether PDE activities in ventricular tissue accurately reflect the isoenzymes present in cardiomyocytes. 2. In homogenates of cardiomyocytes and multicellular ventricular tissue, four distinct soluble PDE activities could be separated by DEAE-sepharose chromatography. 3. In multicellular cardiac tissue as well as in cardiomyocyte preparations, adenosine 3':5'-cyclic monophosphate (cyclic AMP) PDE isoenzymes I-IV were comparable in terms of substrate affinities, and inhibition or stimulation by guanosine 3':5'-cyclic monophosphate (cyclic GMP). However, in cardiomyocytes the Vmax values of PDE I-IV were lower by a factor of about 2 to 7 and the basal activities were lower by a factor of about 3 to 5 as compared to multicellular cardiac tissue. 4. To investigate whether the PDE I-IV activities were similarly inhibited by PDE inhibitors in both preparations, we studied the effects of 3-isobutyl-1-methylxanthine (IBMX), UD-CG 212 Cl (2-(4-hydroxy-phenyl)-5-(5-methyl-3-oxo-4, 5-dihydro-2H-6-pyridazinyl)benzimidazole HCl) and rolipram. UD-CG 212 Cl was a selective PDE III inhibitor in cardiomyocytes (IC50 0.3 mumol l-1) and in ventricular tissue (IC50 value 0.1 mumol l-1). Rolipram selectively inhibited PDE IV in cardiomyocytes (IC50 1.4 mumol ml-1) and in ventricular tissue (IC50 1.1 mumol l-1) whereas IBMX was a nonselective PDE inhibitor in both preparations.5. It is concluded that the PDE isoenzymes I-IV from multicellular ventricular tissue can be used as a representative system for investigating PDE inhibiting properties of PDE inhibitors in the myocardium since comparable PDE isoenzymes I-IV exist in guinea-pig ventricular cardiomyocytes and multicellular ventricular tissue.

Metabolic and renal changes in two athletes during a world 24 hour relay record performance.

Metabolic parameters and renal function were studied in two subjects before, during and after they established a world two-man 24 hour relay record. During the race, the athletes expended an estimated 37.747 and 42.880 kJ running at 54 and 61 per cent of maximum oxygen consumption (VO2max). Rectal temperatures reached maxima of 38.6 and 39.2 degrees C respectively during the race. Serum free fatty acid levels peaked at 2108 and 1875 mumol ml-1 after 24 hours; blood glucose levels varied from 4.3-6.5 and 4.9-8.5 mmol.l-1 respectively. Plasma insulin levels fell from 42.9 and 22.7 microU.ml-1 to 11.5 microU.ml-1. Plasma urea, creatinine, beta 2-microglobulin and C-reactive protein concentrations were elevated at the end of the race (to 9.0 and 8.0 mmol.l-1, 119 and 102 mumol.l-1, 3.508 and 3203 micrograms.l-1 and 2.7 and 3.9 mg per cent respectively). Plasma osmolality was altered from 293 and 304 to 302 and 280 mosmol.Kg-1 during the race but increased to 312 and 318 mosmol.Kg-1 the following day probably due to intercompartmental fluid shifts. Plasma creatinine concentration was increased by 38 and 26 per cent due to reduced urinary excretion. Urine flow rate increased 40 and 123 per cent respectively during the race, but creatinine clearance decreased by 38 and 40 per cent. Urine osmolality decreased by 38 and 65 per cent and osmolal clearance decreased by 15 and 16 per cent respectively. Urine sodium excretion was greatly reduced (85 and 90 per cent) on the post-race days (by 88 and 92 per cent on day 2). Both urine total protein and beta2-microglobulin excretion increased during the race (by 89 and 35 per cent and by 334 and 136 per cent respectively), but owing to the increased beta2-microglobulin production renal clearance was unaltered. The changes in renal function were temporary and some aspects of renal tubular function were enhanced during the post-race days. We conclude that, although C-reactive protein concentrations increased sooner and were higher than other shorter events and although creatinine, urine excretion and urine osmolality decreased markedly, the intermittent nature of the event, the mild environmental conditions, the moderate percentage of VO2 max maintained by the well conditioned subjects and a high fluid intake enabled a rapid return to normality and indeed to enhanced renal tubular function. The only moderate increases in body temperature would be due to the same factors.

Neurotensin modulates the binding characteristics of dopamine D2 receptors in rat striatal membranes also following treatment with toluene

The effects of neurotensin in vitro (1-100 nM) on the binding characteristics of [3H]N-propylnorapomorphine ([3H]NPA) were analysed in striatal membrane preparations of the adult male rat. Subsequently, it was investigated whether the modulatory effects of 10 nM neurotensin on [3H]NPA binding were altered by treatment with toluene in vivo (80 p.p.m., 3 days, 6 h day-1) and in vitro (19 mumol ml-1). Displacement of [3H]NPA binding by raclopride (IC50 about 15 nM) and SCH 23390 (without effect) indicated that [3H]NPA labelled only D2 dopamine receptors in the present study. Neurotensin was found to reduce the affinity of D2 receptors with a maximum response at 10 nM. At this concentration the KD value was increased by 30-40% without any consistent changes in the number of binding sites. The modulatory effect of neurotensin remained intact also following toluene treatment in vivo and in vitro, although at a higher KD range, since toluene alone increased the KD value of [3H]NPA binding by 40-50%. Thus, the mechanisms mediating the effects of neurotensin and toluene on the D2 receptor are likely to be different. When neurotensin and toluene treatments were combined, the KD values of [3H]NPA binding were about twice as high as in non-treated controls. These additive effects may lead to a severely decreased efficiency of dopamine D2-mediated neurotransmission in vivo.

Skeletal muscle and whole body protein turnover in cardiac cachexia: influence of branched-chain amino acid administration.

Muscle protein wasting commonly accompanies severe heart failure. The mechanism of this so-called cardiac cachexia has been investigated in eight patients with an average body weight decrement of 19%, whose results have been compared with those from 11 healthy control subjects. Exchanges of tyrosine and 3-methylhistidine across leg tissue were used as specific indicators of net protein balance and myofibrillar protein breakdown, respectively. Whole body protein turnover was measured using a stable isotope labelling technique with L-[1-13C]leucine as tracer. In patients with cardiac cachexia there were greater values, relative to those values in normal control subjects, of leg efflux of tyrosine (-8.1 +/- 0.6 nmol 100 ml leg tissue-1 min-1 vs. -4.2 +/- 0.3 nmol 100 ml-1 min-1 (P less than 0.01) and of 3-methylhistidine (-0.8 +/- 0.1 nmol 100 ml leg tissue-1 min-1 vs. -0.1 +/- 0.02 nmol 100 ml-1 min-1 (P less than 0.005), mean +/- SEM). The results suggest that in patients with cardiac cachexia the state of net negative protein balance across leg tissue is associated with an increased rate of myofibrillar protein breakdown. In cardiac cachexia, neither efflux of tyrosine (-8.4 +/- 0.7 nmol 100 ml leg tissue-1 min-1) nor of 3-methylhistidine (-1.0 +/- 0.2 nmol 100 ml leg tissue-1 min-1) were significantly altered by branched-chain amino acid (BCAA) infusion to plasma concentrations of 1300 +/- 14 mumol ml-1, i.e., four times normal plasma values (282 +/- 11 mumol ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular pH, lactate, and energy metabolism in neonatal brain during partial ischemia measured in vivo by 31P and 1H nuclear magnetic resonance spectroscopy.

Sequential 31P and 1H nuclear magnetic resonance spectra were measured for neonatal piglets (n = 7) to determine the relationship between brain intracellular pH (pHi), lactate, and phosphorylated energy metabolites during partial ischemia. Simultaneous determinations of arterial and cerebral venous blood gases, pH, O2 content, and plasma concentrations of glucose and lactate were also made. Ischemia, induced by bilateral carotid artery ligation plus hemorrhagic hypotension for 35 min, resulted in variable reductions in ATP, phosphocreatine, and increases in Pi, H+, and lactate relative to control levels. In four piglets, whose arterial blood glucose rose above control, brain lactate exceeded 20 mumol g-1 with corresponding decreases in pHi of greater than 0.7 units compared to control levels. The extents of brain acidosis and lactosis showed a strong linear correlation with each other (r = 0.94). Maximal changes in brain lactate, pHi, and ATP at the end of ischemia showed significant positive linear correlations with the control levels of arterial blood glucose, but did not correlate with arterial glucose or arterial cerebral-venous glucose difference values during ischemia. The relationship between pHi and buffer base deficit was comparable to results reported for adult animals up to 20 mumol ml-1. However, in contrast to models proposed for adult brain, the continued linear relationship between pH and higher buffer base levels is most consistent with a theoretical model that assumes the presence of weak acid buffers with pKa values from 6.7 to 5.2.

Effect of nifedipine on myocardial metabolism in patients with unstable angina.

Myocardial glucose metabolism was assessed using 18F-fluorodeoxyglucose and positron emission tomography in 6 normal volunteers, 7 patients with coronary artery disease and stable angina and 15 patients with unstable angina. All studies were carried out on resting, fasting patients. The patients were off treatment and had no evidence of acute myocardial necrosis or ischaemia. A second study investigated the myocardial glucose metabolism of 5 of the patients with unstable angina after treatment with oral nifedipine. In the first study, the metabolic rate for glucose (MRG) was found to be similar in patients with stable angina and normal volunteers (0.023 +/- 0.032 vs 0.012 +/- 0.008 mumol ml-1 min-1, P less than 0.42), whereas the MRG was significantly higher in patients with unstable angina compared with both that of normal volunteers and patients with stable angina (0.084 +/- 0.047 mumol ml-1 min-1, P less than 0.001). In the second study, the MRG of all of the 5 patients with unstable angina studied after the administration of nifedipine was significantly reduced (P less than 0.05), but was still higher than that of the normal controls. The possibility of spontaneous metabolic changes cannot be excluded, but the consistent reduction of the MRG in all 5 patients after the administration of nifedipine suggests that nifedipine has a beneficial effect on myocardial metabolism that could be related to either an increase in myocardial blood flow or to a direct metabolic effect of nifedipine.

A rapid colorimetric assay for the extracellular lipase of Pseudomonas fluorescens B52 using beta-naphthyl caprylate.

Conditions necessary for the determination of crude extracellular lipase activity from Pseudomonas fluorescens B52 using beta-naphthyl caprylate (beta-NC), an 8-carbon ester, as the substrate were examined. Maximum enzyme synthesis occurred at 20 degrees C in pyruvate mineral salts medium containing 1 mM-CaCl2. Bile salts were necessary for enzyme activity; 6 mM-Na taurocholate or Na deoxycholate gave maximum activity but the latter compound was inhibitory at higher concentrations. Activity was optimal in N-Tris[hydroxymethyl]methyl-2-aminoethane sulphonic acid buffer pH 8.0 at 40 degrees C. A comparison of beta-NC with beta-naphthyl butyrate (a 4-carbon ester) and beta-naphthyl myristate (a 14-carbon ester) showed that beta-NC was the best substrate; Km values of 0.0415, 0.141 and 0.200 mM and Vmax values of 67.2, 20.1 and 5.28 mumol ml-1 h-1 were obtained for those substrates respectively. The enzyme was inhibited 50% in its activity against beta-NC by 0.009 mM-EDTA, 0.0007% (w/v) mixed alkyltrimethylammonium bromide and 0.00275% (w/v) Triton X-100. The biochemical properties determined using beta-NC as substrate are consistent with those reported for the lipases of other strains of Ps. fluorescens using natural substrates.