Physiological Acidosis Research Articles

МЕХАНИЗМЫ ВЛИЯНИЯ АЦИДОЗА НА ТОНУС КРОВЕНОСНЫХ СОСУДОВ

The activity of many physiological mechanisms depends on pH, so maintaining a normal pH in the organism is one of the important tasks of homeostasis regulation. Shifts in the acid-base balance can be associated with both pathological and physiological processes. Physiological acidosis in skeletal muscles appears due to physical exercise, as muscle contractions may reduce pH in muscle fibers and interstitium significantly. However, pH normalizes fairly soon after contractions stop. This happens largely owing to the circulatory system that removes metabolites from muscles. Acidosis causes vasodilatation by affecting the activities of numerous mechanisms in vascular smooth muscle and endothelial cells, and by inhibition of the vasoconstrictor effects of the nervous system. Vasodilation and increase of the muscle blood flow are favorable to recovery of the skeletal muscle performance following intense contractions.

Clinical and blood gas analysis of calves conceived by artificial insemination, in vitro fertilization and animal cloning

ABSTRACT: In order for successful extra-uterine adaptation to occur, it is necessary for the neonate to be able to establish its respiratory functions effectively, guaranteeing efficient oxygenation and good vitality. Respiratory disorders are the major cause of death during the neonatal period in cattle, and this mortality is even more significant when it comes to calves originated by in vitro fertilization (FIV) or animal cloning (CA). Blood gas analysis assesses acid-base balance changes effectively, and when associated with the neonate’s clinical examination, provides subsidies for accurate diagnosis and early treatment of neonatal maladaptation. The objective of this study was to study neonates born from artificial insemination (IA) and to compare them to calves conceived by FIV and CA, regarding blood gas and clinical examination. For that, 20 AI calves, 15 FIV calves, and 15 cloned calves were evaluated immediately after calving and at 6, 12, 24 and 48 hours of life. At all experimental times, venous blood samples were collected for blood gas and clinical examination was performed. In the postpartum evaluation, Apgar score and column length and respiratory amplitude measurements were used. IVF animals showed no alterations, resembling Group IA calves. The calves from CA showed more pronounced acidosis postpartum than expected physiological acidosis mixed for neonates, with decreasing values of bicarbonate (HCO3-), and base excess (BE) and the increase in carbon dioxide pressure (PCO2) when compared to the other groups. This disorder may have reflected lower mean values of Apgar scores and increased heart and respiratory rates. Intensive follow-up of these neonates is suggested, with monitoring by clinical and hemogasometric examination for early diagnosis of this condition and treatment based on oxygen therapy and bicarbonate replacement.

The Extracellular Chaperone Haptoglobin Prevents Serum Fatty Acid-promoted Amyloid Fibril Formation of β2-Microglobulin, Resistance to Lysosomal Degradation, and Cytotoxicity

Fibril formation of β2-microglobulin and associated inflammation occur in patients on long term dialysis. We show that the plasma protein haptoglobin prevents the fatty acid-promoted de novo fibril formation of β2-microglobulin even at substoichiometric concentration. The fibrils are cytotoxic, and haptoglobin abolishes the cytotoxicity by preventing fibril formation. Haptoglobin does not alleviate the cytotoxicity of preformed fibrils. Fibrillar β2-microglobulin is resistant to lysosomal degradation. However, the species of β2-microglobulin populated in the presence of haptoglobin is susceptible to degradation. We observed that haptoglobin interacts with oligomeric prefibrillar species of β2-microglobulin but not with monomeric or fibrillar β2-microglobulin that may underlie the molecular mechanism. 1,1'-Bis(4-anilino)naphthalene-5,5'-disulfonic acid cross-linking to haptoglobin significantly compromises its chaperone activity, suggesting the involvement of hydrophobic surfaces. Haptoglobin is an acute phase protein whose level increases severalfold during inflammation, where local acidosis can occur. Our data show that haptoglobin prevents fibril formation of β2-microglobulin under conditions of physiological acidosis (between pH 5.5 and 6.5) but with relatively decreased efficiency. However, compromise in its chaperone activity under these conditions is more than compensated by its increased level of expression under inflammation. Erythrolysis is known to release hemoglobin into the plasma. Haptoglobin forms a 1:1 (mol/mol) complex with hemoglobin. This complex, like haptoglobin, interacts with the prefibrillar species of β2-microglobulin, preventing its fibril formation and the associated cytotoxicity and resistance to intracellular degradation. Thus, our study demonstrates that haptoglobin is a potential extracellular chaperone for β2-microglobulin even in moderately acidic conditions relevant during inflammation, with promising therapeutic implications in β2-microglobulin amyloid-related diseases.

Environmental cues induce a long noncoding RNA–dependent remodeling of the nucleolus

The nucleolus is a plurifunctional organelle in which structure and function are intimately linked. Its structural plasticity has long been appreciated, particularly in response to transcriptional inhibition and other cellular stresses, although the mechanism and physiological relevance of these phenomena are unclear. Using MCF-7 and other mammalian cell lines, we describe a structural and functional adaptation of the nucleolus, triggered by heat shock or physiological acidosis, that depends on the expression of ribosomal intergenic spacer long noncoding RNA (IGS lncRNA). At the heart of this process is the de novo formation of a large subnucleolar structure, termed the detention center (DC). The DC is a spatially and dynamically distinct region, characterized by an 8-anilino-1-naphthalenesulfonate-positive hydrophobic signature. Its formation is accompanied by redistribution of nucleolar factors and arrest in ribosomal biogenesis. Silencing of regulatory IGS lncRNA prevents the creation of this structure and allows the nucleolus to retain its tripartite organization and transcriptional activity. Signal termination causes a decrease in IGS transcript levels and a return to the active nucleolar conformation. We propose that the induction of IGS lncRNA by environmental signals operates as a molecular switch that regulates the structure and function of the nucleolus.

Engineered non-fluorescent Affibody molecules facilitate studies of the amyloid-beta (Aβ) peptide in monomeric form: Low pH was found to reduce Aβ/Cu(II) binding affinity

Aggregation of amyloid-beta (Aβ) peptides into oligomers and amyloid plaques in the human brain is considered a causative factor in Alzheimer's disease (AD). As metal ions are over-represented in AD patient brains, and as distinct Aβ aggregation pathways in presence of Cu(II) have been demonstrated, metal binding to Aβ likely affects AD progression. Aβ aggregation is moreover pH-dependent, and AD appears to involve inflammatory conditions leading to physiological acidosis. Although metal binding specificity to Aβ varies at different pH's, metal binding affinity to Aβ has so far not been quantitatively investigated at sub-neutral pH levels. This may be explained by the difficulties involved in studying monomeric peptide properties under aggregation-promoting conditions. We have recently devised a modified Affibody molecule, ZAβ3(12–58), that binds Aβ with sub-nanomolar affinity, thereby locking the peptide in monomeric form without affecting the N-terminal region where metal ions bind. Here, we introduce non-fluorescent Aβ-binding Affibody variants that keep Aβ monomeric while only slightly affecting the Aβ peptide's metal binding properties. Using fluorescence spectroscopy, we demonstrate that Cu(II)/Aβ(1–40) binding is almost two orders of magnitude weaker at pH 5.0 (apparent KD=51μM) than at pH 7.3 (apparent KD=0.86μM). This effect is arguably caused by protonation of the histidines involved in the metal ligandation. Our results indicate that engineered variants of Affibody molecules are useful for studying metal-binding and other properties of monomeric Aβ under various physiological conditions, which will improve our understanding of the molecular mechanisms involved in AD.

Are Low Birth Weight Infants at Risk for Mineral Disturbance in Early Neonatal Period?

Bacground and Aims: The physiological levels of calcium and magnesium are very unstable in the first few days after birth, due to abrupt interruption of placental supply, low level of PTH and high levels of calcitonin, physiological acidosis. Infants with intrauterine growth retardation and preterm birth are at risk for hypocalcemia or hypomagnesemia. Often asymptomatic they can be undiscovered and untreated. There are a lot of controversies in regards with the physiological low limit of calcium and magnesium; are their values, smaller than those which are biostatistic classified, without any clinical and electrocardiographic aspects, physiological or not for ontogenetic age? The aim of these paper is to establish the incidence of early hypocalcemia and hypomagnesemia in low birth weight infants and the risk factors that impose the cases in a screening program. Methods: Calcium and magnesium were determined in 120 newborns (50 term SGA newborns, 50 prematures and 20 AGA newborns), 48 hours after birth. Results: Hypocalcemia was detected in 16% of term SGA with Rohrer index below 1.8 and 16% of prematures with gestational age under 32 weeks and birth weight below 1500g. Hypomagnesemia was detected in 4% of term SGA and 16% of SGA prematures. 4 term SGA have had hypocalcemia and hypomagnesemia. Onely 5 cases of term SGA with hypocalcemia were simptomatic. Conclusions: Low birth weight infants and severe intrauterine growth retardation are high risk factors for mineral disturbance. Screening is usefull in SGA new bornes with low Rohrer index and prematures under 1500g.

TASK channels are not required to mount an aldosterone secretory response to metabolic acidosis in mice

The stimulation of aldosterone production by acidosis enhances proton excretion and serves to limit disturbances in systemic acid–base equilibrium. Yet, the mechanisms by which protons stimulate aldosterone production from cells of the adrenal cortex remain largely unknown. TWIK-related acid sensitive K channels (TASK) are inhibited by extracellular protons within the physiological range and have emerged as important regulators of aldosterone production in the adrenal cortex. Here we show that congenic C57BL/6J mice with genetic deletion of TASK-1 (K2P3.1) and TASK-3 (K2P9.1) channel subunits overproduce aldosterone and display an enhanced sensitivity to steroidogenic stimuli, including a more pronounced steroidogenic response to chronic NH4Cl loading. Thus, we conclude that TASK channels are not required for the stimulation of aldosterone production by protons but their inhibition by physiological acidosis may contribute to full expression of the steroidogenic response.

Dramatic Aggregation of Alzheimer Aβ by Cu(II) Is Induced by Conditions Representing Physiological Acidosis

The cortical deposition of Abeta is an event that occurs in Alzheimer's disease, Down's syndrome, head injury, and normal aging. Previously, in appraising the effects of different neurochemical factors that impact upon the solubility of Abeta, we observed that Zn2+ was the predominant bioessential metal to induce the aggregation of soluble Abeta at pH 7.4 in vitro and that this reaction is totally reversible with chelation. We now report that unlike other biometals tested at maximal biological concentrations, marked Cu2+-induced aggregation of Abeta1-40 emerged as the solution pH was lowered from 7.4 to 6.8 and that the reaction was completely reversible with either chelation or alkalinization. This interaction was comparable to the pH-dependent effect of Cu2+ on insulin aggregation but was not seen for aprotinin or albumin. Abeta1-40 bound three to four Cu2+ ions when precipitated at pH 7.0. Rapid, pH-sensitive aggregation occurred at low nanomolar concentrations of both Abeta1-40 and Abeta1-42 with submicromolar concentrations of Cu2+. Unlike Abeta1-40, Abeta1-42 was precipitated by submicromolar Cu2+ concentrations at pH 7.4. Rat Abeta1-40 and histidine-modified human Abeta1-40 were not aggregated by Zn2+, Cu2+, or Fe3+, indicating that histidine residues are essential for metal-mediated Abeta assembly. These results indicate that H+-induced conformational changes unmask a metal-binding site on Abeta that mediates reversible assembly of the peptide. Since a mildly acidic environment together with increased Zn2+ and Cu2+ are common features of inflammation, we propose that Abeta aggregation by these factors may be a response to local injury. Cu2+, Zn2+, and Fe3+ association with Abeta explains the recently reported enrichment of these metal ions in amyloid plaques in Alzheimer's disease.

Acidosis alters the hyperthermic cytotoxicity and the cellular stress response

Heat stroke mortality is worsened in the presence of acidosis. Using cell culture as an in vitro model of exertional heat stress, we have shown that physiologic acidosis (pH 6.8) significantly increases cell death from hyperthermia. We have further demonstrated that acidosis augments the heat response of the human HSP70 3′ untranslated region. These studies provide an in vitro model for study of the mechanisms of injury in exertional heat stress.

Stimulation of rat renal phosphoenolpyruvate carboxykinase activity after an intravenous lactic acid load

It is well known that metabolic acidosis attained by ammonium chloride administration leads to an increase in renal gluconeogenesis [ 1,2] through the activation of phosphoenolpyruvate carboxykinase (EC 4.1.1.32) (PEPCK) [3-51. We have reported that muscular exercise (swimming in water at 22” C for 2 h) results in an increase of renal gluconeogenic ability and PEPCK activity, most probably as a result of the metabolic acidosis caused by overproduction of lactate [6-91. To obtain further information about the relations between lactic acidosis and renal metabolism we produced experimental lactic acidosis which could mimic in some way the physiological acidosis accompanying exercise. Then we have studied the activity of PEPCK, the gluconeogenic ability in kidney cortex and the renal content of some intermediates of gluconeogenesis from rats loaded intravenously with lactic acid or sodium lactate. We have also studied the renal response to the infusion of adrenaline, because of the involvement of this hormone in the metabolic events during exercise [lo]. Our results indicate that induction of renal PEPCK is closely related to acidosis.

Renal reabsorption of bicarbonate in puppies: effect of extracellular volume contraction on the renal threshold for bicarbonate.

Extract: It has been recognized for many years that infants have lower concentrations of bicarbonate in plasma than older children and adults, due neither to a limited renal capacity to excrete hydrogen ion nor to a reduced capacity for reabsorption of bicarbonate, but to a low renal threshold for bicarbonate. The purpose of the present investigation was to determine whether the neonate and young of another species also could be shown to have a “physiologic acidosis” and, if so, to use this model for exploration of factors that might influence the threshold for bicarbonate. Mean pH of blood and concentration of bicarbonate in plasma in 11 young suckling puppies were 7.24 ± 0.018 and 18.2 ± 0.55 mmoles/liter, respectively, levels considerably lower than those found in adult dogs. In all but one animal pH of urine was below 6.0. Inasmuch as puppies thus appear to be in a state of “physiologic acidosis” and to have no limitation in acidification of the urine, we feel that this animal provides a suitable model for further examination of the characteristics of renal reabsorption and excretion of bicarbonate during immaturity. Titrations of bicarbonate performed in the usual manner demonstrated a threshold of 17–20 mmoles/liter, with a mean of 18.3. In the absence of significant volume expansion, maximal rates of reabsorption of bicarbonate were not observed despite filtered loads that were double those at threshold. Fractional excretion of sodium during control periods in animals which were not dehydrated averaged 2.9 ± 1.8% compared with 0.16 ± 0.08% in animals which were slightly dehydrated by their previous treatment with ammonium chloride. In this group, by replacement of gastric fluid (primarily sodium and potassium chloride) with a solution of sodium and potassium bicarbonate, renal handling of bicarbonate at varying filtered loads could be studied in the absence of volume expansion and with the continued stimulus for reabsorption of sodium. Under these circumstances, the renal threshold for bicarbonate was found to be markedly increased (25.2 ± 1.12). Saline was administered to two animals after the threshold had been passed. At any given level of filtered load the rate of excretion of bicarbonate in urine after administration of saline greatly exceeded the rate of excretion during gastric suction. The data in the present study thus indicate that the decreased threshold for bicarbonate in the young animal is not due to a limitation in intrinsic capacity for reabsorption of bicarbonate, inasmuch as capacity could be increased markedly under the stimulus

Renal Bicarbonate Reabsorption and Hydrogen Ion Excretion in Normal Infants*

After acute administration of ammonium chloride, infants 1 to 16 months of age were similar to older children in their capacity to acidify their urine. The infants had a higher rate of excretion of titratable acid and a lower rate of excretion of ammonium but were similar in their rate of excretion of total hydrogen ion.Bicarbonate titrations performed in infants during the first year of life demonstrated a threshold ranging from 21.5 to 22.5 mmoles per L, maximal rate of reabsorption from 2.6 to 2.9 mmoles per 100 ml glomerular filtrate, and marked titration splay. A nephronic frequency distribution curve of the ratio of glomerular filtration rate to tubular reabsorptive capacity demonstrated both heterogeneity and skewing to the right, suggesting the presence of significant numbers of nephrons with low tubular transport capacity relative to filtration rate.It is suggested that the "physiologic acidosis" of the infant is due neither to a limited renal capacity to excrete hydrogen ion nor to a reduced capacity for reabsorption of bicarbonate, but rather to a low renal plasma bicarbonate threshold. Although the level of the threshold may relate to the kinetics of bicarbonate reabsorption during this period, it appears to be due at least in part to functional and morphologic heterogeneity of nephrons.

THE ACIDOTIC STATE OF NORMAL NEW-BORNS

The work of Ylippo, in 1914, was a stimulus to the study of this subject in new-borns. He claims to have found (1) that the human organism at birth is in a state of physiologic acidosis; (2) that the blood shows an acidotic constitution (he having found the P H of the blood to be as low as 6.58); (3) that the CO 2 dissociation curve of the blood of new-borns shows an acidosis (20 per cent. less than in adults), and (4) that the hydrogen concentration is uniformly higher than in adults. Of the many methods for determining acidosis, the two most accurate are, first, the chemical study of the blood, and second, the study of the CO 2 alveolar tension. The method for determining the CO 2 alveolar tension is simple and in most conditions an accurate one for determining acidosis. So far as we know this has