Biochemical medicine and metabolic biology最新文献

The present study examined the effects of acute cocaine administration on oxygen pressure in the vasculature of the cortex as well as on blood dow and extracellular levels of dopamine in the striatum of newborn piglets. The oxygen dependent quenching of phosphorescence was used to continuously monitor oxygen pressure in the vasculature of the cortex. Following acute cocaine injection (1.5 mg/kg iv) the cortical oxygen pressure rapidly decreased from 36.3 ± 1.2 to 32.9 ± 1.4 Torr and remained at the lower level during the 120 min of postinjection period during which measurements were made. Blood dow in striatum, as determined by laser Doppler, was decreased by 8-10% at 5 min after injection of cocaine. This decrease in blood flow was statistically significant up to 40 min postinjection. Extracellular dopamine, measured using in vivo micro dialysis, showed a large increase after cocaine injection. The dopamine level increased from 14 ± 7 to 88 ± 21 pmol/ml by 15 min after drug administration, then decreased to 45 ± 11 pmol/ml and remained stable for the 120 min post-injection period. The mechanism(s) by which the increase in the extracellular level of dopamine occurred may include a direct effect of cocaine on the dopamine transporter and/or an indirect effect due to the decrease in cerebral oxygenation and blood flow. The increase in extracellular dopamine can be responsible for several alterations in neuronal metabolism with potentially deleterious effects on neuronal function.

Interest in β-carotene (BC) has increased as studies show that low dietary or serum BC is associated with increased risk of cancer. Patients with oral epithelial dysplasia had serum and oral mucosa punch biopsy samples taken before supplementation of 30 mg/day of β-carotene and after 6 and 9 months of supplementation. BC was analyzed for 28 patients by high-performance liquid chromatography. At baseline, serum BC and gender accounted for 48% of tissue BC variance: $\text{Tissue BC = −0.13 + 0.08(Serum BC) + 1.21(Sex)}$ with sex as male = 0 or female = 1. Following supplementation, serum BC had an exponential relationship to tissue BC which accounted for 52% of tissue variance: $\text{Tissue BC = 1.15 + 5.7 × 10}{}^{\mathrm{-5}}\text{(Serum BC)}{}^2\text{+ 3.91(Sex).}$ Women had higher mean concentrations of serum and oral mucosal BC before and during supplementation. The need for oral mucosal sampling may be eliminated by the correlation between serum and tissue BC.

High total activity (expressed as μmol/min/g of wet tissue or per milligram of DNA) and differential subregional distribution of NADP-linked malic enzyme was found in autopsy specimens of human brain. Striatum showed the highest activity of malic enzyme, which was two to five-fold higher than that in other human organs tested. High activity was also found in frontal cortex, while the lowest activity of the enzyme in the central nervous system was found in cerebellum, substantia alba, and corpus callosum. In striatum, frontal cortex, pens, and cerebellum more than 80% of total malic enzyme activity was localized in the mitochondrial fraction, while in substantia alba and corpus callosum approximately 60% of the enzyme activity was present in the mitochondrial fraction. Relatively high specific activity of malic enzyme was found in a crude mitochondrial fraction isolated from various regions of human brain. The highest specific activity was found in the mitochondria isolated from striatum (more than 100 nmol/min/mg of mitochondrial protein); the lowest, but still high (approximately 32 nmol/min/mg of mitochondrial protein) was present in corpus callosum. These data and the different ratios of citrate synthase to mitochondrial malic enzyme activities found in different regions of brain suggest that human brain mitochondria, like the mitochondria isolated from other mammalian brains, are extremely heterogenous. A possible role of mitochondrial malic enzyme in human brain metabolism is discussed.

The lens has a very high content of UDP sugars. These are required for glycoprotein and proteoglycan synthesis, as components of fiber cell membranes and the capsule. In diabetes, changes in these sugar nucleotides are related to pathological changes in the basement membranes of cells from non-insulin-requiring tissues. We have investigated whether this is the case in the lens in diabetes and we report here that UDP-sugar levels are, in contrast to the norm in other non-insulin-requiring tissues, decreased at 2 and 4 weeks of diabetes. This is despite an elevation in the precursors of their formation, both of the pyrimidine (PPRibP) and carbohydrate (glucose, glucose 6-phosphate) components. Also reported here is the observation that lens pyrimidine biosynthesis occurs primarily by the de novo route, and that orotate phosphoribosyltransferase and orotidine-5′-phosphate decarboxylase are unchanged in diabetes. We have measured the energy charge of the adenine and uridine nucleotide pools and report both to be compromised under the diabetic condition. The fall in ATP provision is proposed to be responsible for the fall in UTP and hence leads to the recorded decrease in the UDP sugars. These changes are discussed in relation to the change in capsular and fiber cell composition and the functional significance of this in cataract formation.

Ornithine decarboxylase, a modulator of tissue growth during fetal and neonatal mammalian development, serves as a sensitive marker enzyme for perturbations in neural development. To test the hypothesis that cocaine is a central nervous system neurodevelopmental teratogen through mechanisms involving direct cellular injury, we measured ornithine decarboxylase activity in brain sections of 4- to 6-day-old rabbit pups which were prenatally cocaine exposed and in pair-fed and free-fed controls. Rabbit does were implanted with the osmotic minipump prior to Gestational Day 10 and cocaine and/or sterile water was delivered between Gestational Days 10 and 32. The flow rate in the cocaine group was calculated to provide a daily cocaine dose of 30 mg/kg/day. Pups were sacrificed, brains were dissected into the cortex, pons, and medulla, and ornithine decarboxylase activity was measured. When compared to the pair-fed group, prenatal cocaine exposure significantly decreased ornithine decarboxylase activity in the cortex (0.531 ± 0.070 nmol/g/h SEM vs 0.913 ± 0.201 nmol/g/h SEM; cocaine vs pair fed, respectively; P ≤ 0.05) and in the pons (0.533 ± 0.036 nmol/g/h SEM vs 0.728 ± 0.075 nmol/g/h SEM, cocaine vs pair fed, respectively; P ≤ 0.05) but not in the medulla (0.374 ± 0.040 nmol/g/h SEM vs 0.392 ± 0.045 nmol/g/h SEM, cocaine vs pair fed, respectively; P > 0.05). Although there were no statistically significant differences in ornithine decarboxylase activity between the cocaine-exposed group and the free-fed group in any brain region, all regions showed a relative decrease in ornithine decarboxylase activity with prenatal cocaine exposure. These data support the concept that prenatal cocaine exposure and malnutrition play a role in the adverse central nervous system outcomes associated with prenatal cocaine exposure.

We investigated changes in the kinetic characteristics of copper absorption at three stages of rat development: suckling, weanling, and adolescence, as well as the inducibility of metallothionein (MT) in small intestine and kidney. Using an in vivo, single-pass intestinal perfusion procedure, we found that the rates of copper absorption in suckling and weanling rats were concentration-dependent and there was no difference between these two groups of rats. However, in adolescent rats, there was a saturable component, with an apparent K_t of 10-13 μM, and a nonsaturable component with a diffusion coefficient of 3.2 s⁻¹ (3.2 × 10 cm²/s). Intestinal copper retention was also concentration-dependent; the suckling rats showed much greater tissue levels of this element than the weanlings or the adolescents. MT intestinal content after stimulation with ip zinc chloride was significantly higher in the adolescent rats than that in the weanlings and sucklings, indicating that physiological mechanisms other than MT induction may play a role in copper retention early in life. The increase in MT levels in adolescence may be related to the onset of copper absorption saturability in the mature small intestine.

We evaluated the effect of Quin-2 loading (> 20 μM) on platelet responses such as phosphoinositide turnover, elevation of cytosolic Ca²⁺, phosphorylation of myosin light chain (MLC) and a 47-kDa protein, and aggregation in human platelets stimulated with arachidonic acid (AA) and epinephrine. The formation of inositol phosphates (IP, IP₂, and IP₃) in platelets stimulated with AA was inhibited by 50.4, 59.5, and 61%, respectively, in the presence of Quin-2 (40 μM). A similar degree of inhibition was observed in platelets stimulated with epinephrine (50 μM) and thrombin (0.1 U/ml). Even though Quin-2-induced inhibition of aggregation in response to AA was reversed by epinephrine, its effect on phosphoinositide turnover remained unaffected. Monitoring of cytosolic Ca²⁺ changes further indicates that the ability of epinephrine to restore aggregation in Quin-2-loaded (40 μM) and AA-stimulated platelets is not coupled to an increase in cytosolic Ca²⁺. Quin-2 loading (40 μM) caused a significant inhibition of MLC phosphorylation (20 kDa) in platelets stimulated by AA. However, it had no effect on the phosphorylation of the 47-kDa protein induced by AA. Furthermore, Quin-2 loading (40 μM) exerted no significant effect on shape change, actin filament assembly, and spreading, but caused a significant inhibition of secretion and clot retraction. We conclude that the formation of inositol phosphates, increases in cytosoloic Ca²⁺ and phosphorylation of MLC affected by Quin-2 are not coupled to the mechanisms by which platelets develop stickiness, undergo shape change, spreading, and aggregation in response to epinephrine and AA. It appears that the effect of epinephrine in restoring the aggregation response of refractory platelets is coupled to a calcium-mediated α-adrenergic receptor, and it may serve as a critical salvage pathway in platelets with compromised functions.

A high-affinity Ca²⁺-ATPase was solubilized from rat parotid plasma membranes and purified by concanavalin A and DEAE-cellulose chromatography. The properties of the purified high-affinity Ca²⁺-ATPase are very different from those of the parotid plasma membrane ATP-dependent Ca²⁺ pump but appear to be similar to those of a rat liver cell adhesion protein which exhibits high-affinity ecto-Ca²⁺-ATPase activity.