Do blood parasites increase immature erythrocytes and mitosis in amphibians? / ¿Causan los parásitos sanguíneos un aumento en los eritrocitos inmaduros y la mitosis en los anfibios?

Abstract Introduction: In amphibians, blood may act as a hematopoietic tissue. However, the knowledge concerning hematological features is scarce, there is not much information that allows an analysis about the possible explanations of this physiological feature. Objective: This study aimed to evaluate the relationship between immature red blood cells (RBCs) mitosis and the presence of blood parasites in amphibians. Methods: We sampled 116 amphibians (31 species) in six Colombian localities. Blood was taken by cardiac puncture or maxillary vein puncture. Smears were prepared, fixed, and Giemsa stained for microscopical analysis. The variables analyzed were the percentage of immature RBCs, mitotic cells in peripheral blood, and blood parasite infection. Data were analyzed using Wilcoxon's rank test and exact Fisher statistical tests. Results: Sixty-two individuals showed mitosis in peripheral blood, and these mitotic RBCs shared morphological features with immature RBCs. Overall, parasite prevalence was 30.1 %, distributed as follows: Trypanosoma (24.1 %), Hepatozoon-like (6 %), Dactylosoma (4.3 %), Karyolysus-like (0.9 %), and Filarioidea (2.6 %). A positive association between the percentage of immature RBCs and the presence of mitotic RBCs was found, and also between the blood parasite infection and the percentage of immature RBCs. Conclusions: In this study, we found that the presence of blood parasites, immature RBCs, and RBCs mitosis are frequent events in amphibians' peripheral blood, and our analysis suggests an association between those features. Thus, the release of immature RBCs and the mitosis of those cells in peripheral blood may be a physiological response to blood parasite infection. Further studies characterizing hematology in amphibians and wildlife, in general, are desirable.

Resumen Introducción: En anfibios, la sangre puede actuar como un tejido hematopoyético. Sin embargo, el conocimiento acerca de las características hematológicas es escaso y no hay información que permita un análisis acerca de las posibles explicaciones a este rasgo fisiológico. Objetivo: La intención de este estudio fue evaluar la relación entre la presencia de eritroblastos, mitosis de glóbulos rojos (GRs) y la infección por hemoparásito en sangre periférica de anfibios. Métodos: Se muestrearon 116 anfibios (31 especies) en seis localidades de Colombia. Se tomaron muestras de sangre mediante punción cardiaca o punción a la vena maxilar. Se prepararon extendidos sanguíneos, se fijaron y tiñeron con Giemsa para su posterior análisis por microscopía. Se analizaron variables como porcentaje de GRs inmaduros, células mitóticas en sangre periférica e infección por hemoparásitos. Los datos fueron analizados mediante el test de rango de Willcoxon y el test exacto de Fisher. Resultados: sesenta y dos individuos evidenciaron mitosis en sangre periférica y dichas mitosis compartían características morfológicas con GRs inmaduros. La prevalencia general de parásitos fue del 30.1 %, distribuido de la siguiente forma: Trypanosoma (24.1 %), Hepatozoon-like (6 %), Dactylosoma (4.3 %), Karyolysus-like (0.9 %), y Filarioidea (2. 6 %). Hay una asociación positiva entre el porcentaje de GRs inmaduros y la presencia de células mitóticas, también se encontró una relación entre la infección por hemoparásitos y el porcentaje de GRs inmaduros. Conclusiones: En este estudio encontramos que la presencia de parásitos sanguíneos, GRs inmaduros y mitosis de GRs son eventos frecuentes en sangre periférica de anfibios, y nuestros resultados sugieren una asociación entre dichas características. Por tanto, la liberación de GRs inmaduros y la mitosis de estas células en sangre periférica podría ser una respuesta fisiológica a infecciones parasitarias. Posteriores estudios que caractericen la hematología en anfibios y en vida silvestre en general, son deseables.

POPULATION PHARMACOKINETICS OF CEFTAZIDIME AFTER A SINGLE SUBCUTANEOUS INJECTION AND NORMAL ORAL AND CLOACAL BACTERIAL FLORA SURVEY IN EASTERN HELLBENDERS (CRYPTOBRANCHUS ALLEGANIENSIS ALLEGANIENSIS).

Population pharmacokinetics utilizing sparse sampling were used to determine pharmacokinetics of ceftazidime in eastern hellbenders (Cryptobranchus alleganiensis alleganiensis) due to their slow growth rate and the limited number of appropriately sized individuals in the zoo-housed population. Twenty-five eastern hellbenders received a single subcutaneous injection of ceftazidime at 20 mg/kg. Each animal had blood samples collected up to four times between 0 and 192 hr postinjection. Plasma samples were analyzed by high-pressure liquid chromatography. A nonlinear mixed-effects model was fitted to the data to determine typical values for population parameters, an ideal method due to the sampling limitation of each hellbender. Results indicate an elimination half-life of 36.63 hr and volume of distribution of 0.31 L/kg. Antibiotic concentrations were above a minimum inhibitory concentration (MIC) value of 8 µg/ml for 120 hr. Prior to antibiotic administration, six hellbenders had oral and six other individuals had cloacal swabs taken for aerobic culture. Fifty-five bacterial isolates were obtained (24 cloacal, 31 oral) with 10/12 (83%) individuals growing three or more different isolates and 11/12 (92%) growing Shewanella putrefaciens. Twelve isolates had susceptibility testing performed and all were susceptible to ceftazidime. These results indicate that ceftazidime is an appropriate choice of antibiotic in hellbenders and when given at a dosage of 20 mg/kg subcutaneously, maintains concentrations above the MIC of susceptible bacteria for up to 5 days.

Multilocus Metabarcoding of Terrestrial Leech Bloodmeal iDNA Increases Species Richness Uncovered in Surveys of Vertebrate Host Biodiversity.

Leech-derived invertebrate DNA (iDNA) has been successfully leveraged to conduct surveys of vertebrate host biodiversity across the Indo Pacific. However, this technique has been limited methodologically, typically only targeting mammalian 16S rDNA, or both 16S and vertebrate 12S rDNA for leech host determination. To improve the taxonomic richness of vertebrate host species in iDNA surveys, we re-analyze datasets from Bangladesh, Cambodia, China, and Madagascar through metabarcoding via next generation sequencing (NGS) of 12S, 16S (2 types, one designed to target mammals and the other, residual eDNA), nicotinamide adenine dinucleotide hydride dehydrogenase 2 (ND2), and cytochrome c oxidase subunit 1 (COI). With our 5 primer sets, we identify 41 unique vertebrate hosts to the species level, among 1,200 leeches analyzed, along with an additional 13 taxa to the family rank. Within our 41 taxa, we note that adding ND2 and COI loci increased species richness detection by 25%. NGS has emerged as more efficient than Sanger sequencing for large scale metabarcoding applications and, with the decline in cost of NGS, our pooled sample multilocus protocol is an attractive option for iDNA biodiversity surveys.

Right-to-left shunt has modest effects on CO2 delivery to the gut during digestion, but compromises oxygen delivery.

By virtue of their cardiovascular anatomy, reptiles and amphibians can shunt blood away from the pulmonary or systemic circuits, but the functional role of this characteristic trait remains unclear. It has been suggested that right-to-left (R-L) shunt (recirculation of systemic blood within the body) fuels the gastric mucosa with acidified and CO2-rich blood to facilitate gastric acid secretion during digestion. However, in addition to elevating PCO2 , R-L shunt also reduces arterial O2 levels and would compromise O2 delivery during the increased metabolic state of digestion. Conversely, arterial PCO2  can also be elevated by lowering ventilation relative to metabolism (i.e. reducing the air convection requirement, ACR). Based on a mathematical analysis of the relative roles of ACR and R-L shunt on O2 and CO2 levels, we predict that ventilatory modifications are much more effective for gastric CO2 supply with only modest effects on O2 delivery. Conversely, elevating CO2 levels by means of R-L shunt would come at a cost of significant reductions in O2 levels. The different effects of altering ACR and R-L shunt on O2 and CO2 levels are explained by the differences in the effective blood capacitance coefficients.

Identification of Blood Meals from Potential Arbovirus Mosquito Vectors in the Peruvian Amazon Basin.

The transmission dynamics of many arboviruses in the Amazon Basin region have not been fully elucidated, including the vectors and natural reservoir hosts. Identification of blood meal sources in field-caught mosquitoes could yield information for identifying potential arbovirus vertebrate hosts. We identified blood meal sources in 131 mosquitoes collected from areas endemic for arboviruses in the Peruvian Department of Loreto by sequencing polymerase chain reaction amplicons of the cytochrome b gene. Psorophora (Janthinosoma) albigenu, Psorophora (Grabhamia) cingulata, Mansonia humeralis, Anopheles oswaldoi s.l., and Anopheles benarrochi s.l. had mainly anthropophilic feeding preferences; Aedes (Ochlerotatus) serratus, and Aedes (Ochlerotatus) fulvus had feeding preferences for peridomestic animals; and Culex (Melanoconion) spp. fed on a variety of vertebrates, mainly rodents (spiny rats), birds, and amphibians. On the basis of these feeding preferences, many mosquitoes could be considered as potential enzootic and bridge arbovirus vectors in the Amazon Basin of Peru.

Evaluation of the blood film.

Evaluation of hemic cell morphology in stained blood film may be the most important part of the hematologic evaluation of exotic animals. The blood film provides important information regarding red blood cell abnormalities, such as changes in cell shape and color, presence of inclusions, and, in the case of lower vertebrates, changes in the position of the cell nucleus. Stained blood film also provides information about changes in leukocyte numbers and morphology, and shows important hemic features of mammalian platelets and the thrombocytes of lower vertebrates. The blood film is needed in the detection and identification of blood parasites.

The immunoglobulins of cold-blooded vertebrates.

Although lymphocyte-like cells secreting somatically-recombining receptors have been identified in the jawless fishes (hagfish and lamprey), the cartilaginous fishes (sharks, skates, rays and chimaera) are the most phylogenetically distant group relative to mammals in which bona fide immunoglobulins (Igs) have been found. Studies of the antibodies and humoral immune responses of cartilaginous fishes and other cold-blooded vertebrates (bony fishes, amphibians and reptiles) are not only revealing information about the emergence and roles of the different Ig heavy and light chain isotypes, but also the evolution of specialised adaptive features such as isotype switching, somatic hypermutation and affinity maturation. It is becoming increasingly apparent that while the adaptive immune response in these vertebrate lineages arose a long time ago, it is most definitely not primitive and has evolved to become complex and sophisticated. This review will summarise what is currently known about the immunoglobulins of cold-blooded vertebrates and highlight the differences, and commonalities, between these and more "conventional" mammalian species.

Experimental infection dynamics: using immunosuppression and in vivo parasite tracking to understand host resistance in an amphibian-trematode system.

Although naturally occurring hosts often exhibit pronounced differences in infection and pathology, the relative importance of factors associated with host life history and immunity in explaining such patterns often remains speculative. Research in eco-immunology highlights the trade-offs between host physiology and immunity, for which natural variations in disease susceptibility offer a valuable platform to test predictions within this framework. Here, we combined use of a novel, in vivo assay for tracking parasite fate and an experimental manipulation of host immune function (via chronic corticosterone exposure) to assess the role of host immunity in regulating susceptibility of amphibian hosts to three larval trematodes: Ribeiroia ondatrae, Echinostoma trivolvis and Alaria sp. 2. Results from the in vivo parasite-tracking assay revealed marked differences in initial parasite penetration and subsequent host clearance. Relative to infections in a highly susceptible species (Pseudacris regilla), the virulent trematode R. ondatrae was -25% less successful at penetrating larvae of three hylid frog species and was cleared > 45(×) faster, such that all parasites were rapidly cleared from hylid hosts over 72 h following a Weibull distribution. Immune suppression of Hyla versicolor sharply reduced this resistance and increased infection of all three trematodes by 67 to 190%, with particularly strong increases for R. ondatrae. Diminished resistance correlated with a 62% decrease in circulating eosinophils. Correspondingly, 10 days after corticosterone exposures ended, infections declined dramatically while eosinophil levels returned to normal. In light of ongoing declines and deformities in amphibian populations, these findings have application potential for mitigating disease-driven effects.

[Ratio of cations in hemolymph, blood serum of aquatic and terrestrial organisms].

A wide range of differences of cations concentrations (Na, K, Ca, Mg) in hemolymph, blood serum of multicellular animals and humans was revealed. It was established that constancy of K/Na ratio 0.034 +/- 0.001 is strictly maintained in these organisms. Except for some freshwater and marine organisms, Mg/Na ratio is sustained on the same level in the wide range of concentrations of these ions in serum of vertebrates and hemolymph of invertebrates. Ca/Na ratio is higher in hemolymph of freshwater mollusks. The question about possible reasons of physiological differences of Ca/Na and Mg/Na rations compared to constancy of K/Na ratio is discussed.

Variation in testosterone and corticosterone in amphibians and reptiles: relationships with latitude, elevation, and breeding season length.

Latitudinal variation in life-history traits has been the focus of numerous investigations, but underlying hormonal mechanisms have received much less attention. Steroid hormones play a central role in vertebrate reproduction and may be associated with life-history trade-offs. Consequently, circulating concentrations of these hormones vary tremendously across vertebrates, yet interspecific geographic variation in male hormone concentrations has been studied in detail only in birds. We here report on such variation in amphibians and reptiles, confirming patterns observed in birds. Using phylogenetic comparative analyses, we found that in amphibians, but not in reptiles, testosterone and baseline corticosterone were positively related to latitude. Baseline corticosterone was negatively related to elevation in amphibians but not in reptiles. For both groups, testosterone concentrations were negatively related to breeding-season length. In addition, testosterone concentrations were positively correlated with baseline corticosterone in both groups. Our findings may best be explained by the hypothesis that shorter breeding seasons increase male-male competition, which may favor increased testosterone concentrations that modulate secondary sexual traits. Elevated energetic demands resulting from greater reproductive intensity may require higher baseline corticosterone. Thus, the positive relationship between testosterone and corticosterone in both groups suggests an energetic demand for testosterone-regulated behavior that is met with increased baseline glucocorticoid concentrations.

Physiological response of American bullfrog tadpoles to stressor conditions of capture and hypoxia / Resposta fisiológica de girinos de rã-touro americana submetidos aos mecanismos estressores de captura e hipóxia

The American bullfrog (Rana catesbeiana), recently named Lithobates catesbeianus is currently farmed for commercial purposes throughout various regions of Brazil. Stressful situations such as problems of management, inadequate facilities and environmental changes with consequent reduction of immunity are common in intensive production. The assessments of these situations of stress allow us detect these problems decreasing the injuries causes by confinement. The main objective of this study was to use the biological markers of plasma cortisol and glucose level and hematological parameters to evaluate the response of bullfrog tadpoles submitted to stressed mechanisms of capture and hypoxia. The animals were subjected to three treatments: stress due to individual capture with a hand net; stress due to batch capture with a hand net; and stress due to capture by emptying. The results obtained demonstrated that there were no statistically significant differences in the parameters tested when comparing the treatments with and without exposure to air (normoxia and hypoxia). Based on these results we can conclude that the stressful stimuli tested were not adequate to alter the biomarker tested. For the cortisol, probably this should have occurred due to the synergistic action between this hormone and thyroxin, which induces metamorphosis in these animals.

A rã-touro americana (Rana catesbeiana) recentemente denominada Lithobates catesbeianus é cria da com propósito comercial em várias regiões do Brasil. Situações estressantes tais como problemas de manejo, criação inadequada e alterações ambientais com consequente redução da imunidade são comuns em produções intensivas. A avaliação destas situações de estresse permite-nos detectar estes probemas e diminuir as injurias causadas pelo confinamento. O principal objetivo deste estudo foi utilizar os marcadores biológicos de cortisol, glicemia e dados hematológicos para avaliar a resposta de girinos de rã-touro submetidos aos mecanismos estressores de captura e hipóxia. Os animais foram distribuídosem três tratamentos: estresse por captura individual com puçá; estresse por captura em massa com puçá e estresse por captura por escoamento. Os resultados obtidos demostraram não haver diferenças estatisticamente significativas entre os parametros avaliados quando comparou-se os grupos com e sem exposição ao ar (normoxia e hipoxia). Com base nestes resultados pode-se concluir que os estímulos estressores avaliados não foram adequados para alterar os valores plasmáticos dos marcadores biológicos testados. Para o cortisol, isto ocorreu provavelmente em virtude da ação sinérgica deste hormônio e a tiroxina, que induz a metamorfose nestes animais.

Red blood cell Na pump: Insights from species differences.

The red blood cell membrane is specialized to exchange chloride and bicarbonate; usually the pH gradient, the chloride ratio, and the membrane potential are tightly coupled. We review the evidence that led to the ability to separately vary inside and outside pH in red cells. The effect of pH on Na pump activity and on the selectivity of the inside and the outside transport sites is reviewed. In red blood cells, at high pH, the outside site is not selective. An increase in protons leads to an increase in K(+) affinity, thus making the site more selective. The pK for this site is different in rats and humans; because of the high conservation of residues in these two species, there are only a few possible residues that can account for this difference. On the inside, work from unsided preparations suggests that, at high pH, the transport site is highly selective for Na(+). Once again, an increase in protons leads to an increase in K(+) affinity, but now the result is a less selective site. During their maturation, reticulocytes lose many membrane proteins. The type and fractional loss is species dependent. For example, most reticulocytes lose most of their Na pumps, retaining about 100 pumps per cell, but animals from the order Carnivora lose all their pumps. We review some of the evidence that PKC phosphorylation of N-terminus serines is responsible for endocytosis in other cell types and species variation in this region.

Amphibian hematology.

Amphibians are a diverse class of animals with a unique life cycle. Intrinsic and extrinsic factors contribute to the wide variability in normal hematologic parameters. Reference values are scarce, and normal hematology of many species is poorly understood. Challenges include analytic obstacles posed by nucleated red blood cells and thrombocytes and potential difficulty with obtaining blood samples of adequate volume and without lymph contamination. Despite these limitations, it is possible to obtain hematologic data that may be useful in assessing an animal's current health, progression of disease, or response to therapy. In this article, amphibian blood sample collection and handling guidelines, hematologic tests, cell morphology and function, hematopoiesis, interpretation of results, and disorders and diseases are described.

A perspective on the role of natriuretic peptides in amphibian osmoregulation.

The natriuretic peptide (NP) system is a complex family of peptides and receptors that is primarily linked to the maintenance of osmotic and cardiovascular homeostasis. In amphibians, the potential role(s) of NPs is complicated by the range of osmoregulatory strategies found in amphibians, and the different tissues that participate in osmoregulation. Atrial NP, brain NP, and C-type NP have been isolated or cloned from a number of species, which has enabled physiological studies to be performed with homologous peptides. In addition, three types of NP receptors have been cloned and partially characterised. Natriuretic peptides are always potent vasodilators in amphibian blood vessels, and ANP has been shown to increase the permeability of the microcirculation. In the perfused kidney, ANP causes vasodilation, diuresis and natriuresis that are caused by an increased GFR rather than effects in the renal tubules. These data are supported by the presence of ANP receptors only on the glomeruli and renal blood vessels. In the bladder and skin, the function of NPs is enigmatic because physiological analysis of the effects of ANP on bladder and skin function has yielded conflicting data with no clear role for NPs being revealed. Overall, NPs often have no direct effect, but in some studies they have been shown to inhibit the function of AVT. In addition, there is evidence that ANP can inhibit salt retention in amphibians since it can inhibit the ability of adrenocorticotrophic hormone or angiotensin II to stimulate corticosteroid secretion. It is proposed that an important role for cardiac NPs could be in the control of hypervolaemia during periods of rapid rehydration, which occurs in terrestrial amphibians.

Identification of reptilian and amphibian blood meals from mosquitoes in an eastern equine encephalomyelitis virus focus in central Alabama.

Uranotaenia sapphirina, Culex erraticus, and Cx. peccator were collected in an enzootic eastern equine encephalomyelitis (EEE) virus focus in central Alabama (Tuskegee National Forest) from 2001 to 2003 and analyzed for virus as well as host selection. EEE virus was detected in each species every year except 2003, when pools of Cx. peccator were negative. Most (97%) of the 130 Cx. peccator blood meals identified were from ectothermic hosts; 3% were from birds. Among blood meals from reptiles (approximately 75% of the total), 81% were from Agkistrodon piscivorus (cottonmouth); all amphibian blood meals (approximately 25%) were from Rana spp. with > 50% taken from the bullfrog R. catesbeiana. Host identifications were made from 131 of 197 Cx. erraticus, but only 3 (2%) were derived from ectothermic species. Identification of Ur. sapphirina blood meals proved difficult and only 2 of 35 hosts were determined. Both were from R. catesbeiana. Ectothermic species are possible EEE virus reservoirs in the southeastern United States where species such as Cx. peccator and Ur. sapphirina occur with large, diverse reptilian, amphibian, and avian populations such as those at the Tuskegee site.

Evolutionary determinants of normal arterial plasma pH in ectothermic vertebrates.

Mean values of normal arterial pH in different species of fish, amphibians and reptiles at 15 and 25 degrees C, taken from the literature, are negatively correlated with arterial P(CO(2)) and plasma [Na(+)]. At either temperature, the data accord with the hypothesis that extracellular acid-base homeostasis evolved to maintain an optimal pH at particular cell-surface sites that are similar in all species. These hypothetical sites bear fixed negative charges that attract H(+), but which are partially screened by Na(+); for the surface pH to be constant, the bulk interstitial pH should then vary inversely with [Na(+)], as is the case. At the same time, the bulk interstitial fluid must be more acid than arterial plasma by an amount that increases with decreasing arterial P(CO(2)). With allowance made for additional screening by Ca(2+) and Mg(2+), the relevant cell-surface pH is probably approximately 6.2.

Differences in pH between interstitial fluid and arterial blood in water-breathing and air-breathing vertebrates.

Most cells are bathed by interstitial fluid, but extracellular pH measurements are mostly for arterial plasma. Whole-body mean pH differences between the two fluids have been estimated in terms of a simple model. This relates to the diffusive exchange of carbon dioxide and oxygen and utilizes literature data, for 22 vertebrate species, on arterial and mixed-venous tensions of both gases. Uncertainties arise because the carbon dioxide reaction in blood may sometimes be in disequilibrium and because carbon dioxide diffusion is facilitated to unknown degrees in the presence of buffers. Nevertheless, the model suggests that the pH difference should tend to vary inversely with arterial carbon dioxide tension. In some species, this may aid interstitial pH homeostasis, but a clearer implication is that the difference should be generally greater in water breathers than in air breathers. It has previously been found that arterial pH in water-breathing teleosts also tends to be higher than in air-breathing tetrapods (when allowance is made for temperature and plasma sodium concentration) and to a comparable extent. Thus, mean interstitial pH may be more nearly similar in the two groups than is arterial pH. Direct measurements of interstitial pH do not yet suffice to test the model.

Self-association, cooperativity and supercooperativity of oxygen binding by hemoglobins.

Cooperative ligand binding by tetrameric vertebrate hemoglobins (Hbs) makes possible the delivery of oxygen at higher pressures than would otherwise occur. This cooperativity depends on changes in dimer-dimer interactions within the tetramer and is reflected in a 50 000-fold increase in the tetramer-dimer dissociation constant in human Hb upon oxygenation at pH 7.4, from approximately 2x10(-11)mol l-1 to approximately 10(-6)mol l-1. Hbs that undergo such ligand-dependent changes in association are widespread in non-vertebrates, where the mechanisms are very different from those in vertebrates. Oligomeric Hbs have been identified in organisms in five phyla (molluscs, echinoderms, annelids, phoronids and chordates) that dissociate to subunits upon oxidation of the heme iron and reassociate with the binding of ferric iron ligands such as CN-, N3- or NO2-. Thus, the valence and ligand state of the heme iron control the stability of a critical subunit interface. The broad distribution of this phenomenon suggests a common mechanism of communication between heme and interface that may be almost universal among non-vertebrate Hbs. This interaction may be similar to that known for the homodimeric Hb of the mollusc Scapharca inaequivalvis. Although muscle tissue Hbs or myoglobins (Mbs) are usually monomeric, with non-cooperative O2 binding, the radular muscles of gastropod molluscs and chitons have homodimeric Mbs that bind O2 cooperatively. Cooperative non-muscle tissue Hbs have also been identified. These include the neural Hb of the nemertean worm Cerebratulus lacteus and the Hb of the diving beetle Anisops assimilis, which exhibit deoxygenation-dependent self-association of monomers that is associated with high Hill coefficients. Calculations suggest that the 2-3 mmol l-1 concentration of Hb on a heme basis in the brain of Cerebratulus should substantially extend the time as an active predator in an anaerobic or hypoxic environment. Oxygen from the Hb of Anisops is delivered to a gas bubble and thereby controls the buoyant density. Many Hbs of amphibians, reptiles, birds and some embryonic mammals exhibit a further 'supercooperativity' of O2 binding which depends on reversible deoxygenation-dependent tetramer-tetramer association to form an assemblage with a very low affinity for O2. This phenomenon results in steeper O2-binding curves than exhibited by tetramers alone. The increased cooperativity should result in an increase in the amount of O2 delivered to the tissues and should be especially valuable for avian flight muscles.

The phylogenetic odyssey of the erythrocyte. IV. The amphibians.

Amphibians manifest permanently nucleated, oval, flattened, biconvex erythrocytes. These cells demonstrate a cytoskeleton which is responsible for their morphogenetic conversion from a sphere to an ellipse and imparts to their cellular mass reversibility of traumatic deformation. The class Amphibia has the largest of all erythrocytes attaining volumes greater than 10,000 femtoliters in the Amphiuma. The large dimensions reflect evolutionary processes, genomic size, ploidy and the relative size of other somatic cells. Conversely, the erythrocyte count and hemoglobin concentration of these species are low. Occasional denucleated red cells can be seen in the peripheral blood but may attain levels of 90-95% of the total circulating population in certain members of the tribe Bolitoglossini (e.g. Batrachoseps attenuatus). These erythroplastids retain the marginal band thus remaining different from mammalian erythrocytes. Embryologically, erythropoiesis initiates in the yolk sac and then progresses to the kidney, liver, and possibly spleen. The yolk sac cohort is transitory and is successively replaced by the larval and definitive populations of erythrocytes. Red cell production (along with thrombocytopoiesis) in adult urodeles is conducted intravascularly in the spleen. In anurans this organ is usually the major site although the liver also serves as a secondary locus for this activity. Medullary (bone marrow) erythropoiesis makes its phylogenetic debut in anurans and typically occurs during heightened hemopoiesis following metamorphosis or hibernation. Maturation of the erythrocyte in the circulation is commonplace (especially in urodeles) while proliferation at this site is inducible by splenectomy and/or hemolysins. Erythrocyte-related values demonstrate variable differences associated with age, weight, season, gender, and environment.

[The species characteristics of the intramolecular structure of hemoglobin in vertebrates]. / O vidovykh osobennostiakh vnutrimolekuliarnoi struktury gemoglobina pozvonochnykh.

Using fluorescence spectroscopy species peculiarity of hydrophobic and microviscosity degree in central and peripheral molecular areas of the main electrophoretic haemoglobin fractions in representatives of different vertebrate classes gas been studied. It is established that central areas of haemoglobin molecule are characterised by twice lesser variability of size and hydrophobic degree and 2.4 times greater variability of package strength as compared with peripheral areas of protein globule.