RND3 Potentiates Proinflammatory Activation through NOTCH Signaling in Activated Macrophages

Macrophage activation is a complex process with multiple control elements that ensures an adequate response to the aggressor pathogens and, on the other hand, avoids an excess of inflammatory activity that could cause tissue damage. In this study, we have identified RND3, a small GTP-binding protein, as a new element in the complex signaling process that leads to macrophage activation. We show that RND3 expression is transiently induced in macrophages activated through Toll receptors and potentiated by IFN-γ. We also demonstrate that RND3 increases NOTCH signaling in macrophages by favoring NOTCH1 expression and its nuclear activity; however, Rnd3 expression seems to be inhibited by NOTCH signaling, setting up a negative regulatory feedback loop. Moreover, increased RND3 protein levels seem to potentiate NFκB and STAT1 transcriptional activity resulting in increased expression of proinflammatory genes, such as Tnf-α, Irf-1, or Cxcl-10. Altogether, our results indicate that RND3 seems to be a new regulatory element which could control the activation of macrophages, able to fine tune the inflammatory response through NOTCH.

Tasas de letalidad por SARS-CoV-2 según Comunidades Autónomas durante la segunda onda epidémica en España

Introducción

En España, los sistemas sanitarios están transferidos a las Comunidades Autónomas (CC.AA.), constituyendo 19 sistemas sanitarios con gestión y recursos diferenciados. Durante la primera onda epidémica de la COVID-19 se objetivaron diferencias en los sistemas de declaración y en las tasas de letalidad (TL) entre las CC.AA. El objetivo de este estudio fue analizar las TL por CC.AA. durante la segunda onda epidémica (del 20 de julio al 25 de diciembre de 2020) y su relación con la prevalencia de la infección.

Material y métodos

Se realizó un estudio observacional descriptivo con la información disponible sobre el número de fallecidos por COVID-19 registrados en el Ministerio de Sanidad, Consejerías de Salud y los Departamentos de Salud Pública de las CC.AA. y según el exceso de mortalidad informado por el Sistema de Monitorización de Mortalidad Diaria (MoMo). La prevalencia de la infección se estimó a partir de las diferencias entre la segunda y cuarta ronda del estudio ENE-COVID y sus intervalos de confianza del 95%. Se calcularon las TL (fallecidos por cada mil infectados) globales, por sexo, grupos de edad (< 65 y ≥ 65 años) y CC.AA. Se calculó la razón estandarizada de letalidad por edad (REL) de las CC.AA. utilizando las TL de España para cada grupo de etario. Estas estimaciones se realizaron con las defunciones declaradas oficialmente (TLo) y el exceso de defunciones estimadas por MoMo (TLMo). Se estimaron las correlaciones entre las prevalencias de infección y las TLo y TLMo, ponderando por población.

Resultados

Para el conjunto de España, la TLo durante la segunda onda epidémica fue del 7,6%, oscilando entre 3,8% de Baleares y 16,4% de Asturias, y la TLMo fue de 10,1%, oscilando entre el 4,8% de Madrid y el 21,7% en Asturias. Se observaron diferencias significativas entre la TLo y la TLMo en Canarias, Castilla la Mancha, Extremadura, Comunidad Valenciana, Andalucía y las Ciudades Autónomas de Ceuta y Melilla. La TLo fue significativamente mayor en hombres (8,2%) que en mujeres (7,1%). Las TLo y TLMo fueron significativamente mayores en el grupo de edad ≥ 65 años (55,4 y 72,2%, respectivamente) que en el grupo < 65 años (0,5 y 1,4%, respectivamente). País Vasco, Aragón, Andalucía y Castilla la Mancha presentaron una REL significativamente superiores a uno. Las correlaciones entre la prevalencia de infección y las TLo fueron inversas.

Conclusiones

La letalidad por COVID-19 durante la segunda onda epidémica en España mejoró respecto a la primera. Los datos disponibles sugieren que la letalidad de la segunda onda en las CC.AA. estaría influida por la elevada letalidad observada en la primera onda en personas con comorbilidades, así como por las limitaciones de los sistemas de detección y notificación de SARS-CoV-2. Las tasas de letalidad fueron mayores en hombres y personas mayores, y variaban significativamente entre CC.AA. Es necesario profundizar en el análisis de las causas de estas diferencias.

Heat rectification with a minimal model of two harmonic oscillators

We study heat rectification in a minimalistic model composed of two unequal atoms subjected to linear forces and in contact with effective Langevin baths induced by Doppler lasers. Analytic expressions of the heat currents in the steady state are spelled out. Asymmetric heat transport is found in this linear system if both the bath temperatures and the temperature-dependent bath-system couplings are exchanged. The model can be realized with two ions in either common or individual traps. This physical setting allows for a natural temperature dependence of the coupling to the baths. We also explore the parameter space of the model to optimize asymmetric heat current and find conditions for maximal rectification. High rectification corresponds to a good match of the power spectra of the ions for forward temperature bias and mismatch for reverse bias, which may be understood by the behavior of dissipative normal modes.

[Analysis of fatality rates case of SARS-CoV-2 infection in the Autonomous Communities of Spain]

INTRODUCTION

The SARS-CoV-2 pandemic has posed a real challenge to health systems. In Spain, the heterogeneous distribution of the virus infection and the different health strategies have conditioned the morbidity and fatality rate. The aim of this study was to analyse the lethality of the infection by sex and age range in the Autonomous Communities (AC) of Spain.

MATERIAL AND METHODS

To perform the analysis, data were extracted from the Ministry of Health, Regional and Public Health Departments of the different AC. The infected population was estimated from the results of the ENE-COVID19 and the population registered on 1 January 2020 (INE) for the validity of the IgG antibody test with 80% sensitivity and 100% specificity. The case fatality rate (TL) (deaths/1000 estimated infected) by sex and age (<20years, 20-64 and ≥65years) was calculated for each AC. The standardized case fatality ratio (REL) was calculated by the exact method (EPIDAT).

RESULTS

The estimated prevalence of SARS-CoV-2 infection in Spain was 6% (range, 1.4% [Ceuta] -14.1% [Community of Madrid]). The TL in Spain was 9,6/1000, ranged per AC from 1/1000 in Melilla to 26.6/1000 in La Rioja, with no correlation between case fatality and prevalence of infection. The TL was higher in men (10.2/1000, ratio 1.17 with respect to women), except in Cataluña (ratio 0.92), and especially high in those over 64years of age in La Rioja (143.5/1000), Asturias (69.2/1000) and Basque Country (46.6/1000). Overall excess REL was found to be over 30% in La Rioja (2.91; 95%CI: 2.36-3.57), Asturias (1.51; 95%CI: 1.27-1.80), Basque Country (1.42; 95%CI: 1.31-1.54) and Extremadura (1.37; 95%CI: 1.20-1.57) and in those over 64 years in Madrid and the Canary Islands.

CONCLUSIONS

SARs-CoV-2 virus infection has been very unevenly distributed in the different ACs, with notably differences in TL between ACs, particularly high in La Rioja, Asturias and the Basque Country. Is important to study the excess in TL the population over 64years of age in the ACs of Madrid and the Canary Islands.

Hyaluronic acid biomaterial for human tissue-engineered skin substitutes: Preclinical comparative in vivo study of wound healing

BACKGROUND

There is not an ideal biomaterial for tissue-engineered skin substitutes (TESSs), and most of the studies or existing therapies use xenogeneic origin natural biomaterials or biosynthetic scaffolds.

OBJECTIVE

To analyse clinical, histological integration and homeostasis parameters of a human TESS manufactured with fibrin-hyaluronic acid biomaterial (HA-Skin), grafted in immunodeficient mice for 8 weeks, and compared with the gold standard treatment (Autograft), a human TESS manufactured with fibrin-agarose biomaterial (AG-Skin) and secondary wound healing dressings.

METHODS

Human TESSs and autografts were implanted into BALB/c mice after surgical excision. Secondary wound healing approach was achieved with biosynthetic collagen wound dressing (Biobrane^® ) and fibrin-hyaluronic acid or fibrin-agarose biomaterial without cells (Total N = 44). Clinical integration and homeostasis parameters were evaluated every two weeks for two months. Histological and immunohistochemical analyses were performed four and eight weeks after grafting.

RESULTS

HA-Skin, AG-Skin and Autograft groups showed a proper clinical integration and epithelization eight weeks later. Scar evaluation revealed better results for Autograft and HA-Skin. Homeostasis analysis indicated similar values of transepidermal water loss and elasticity between HA-Skin (6.42 ± 0.75 g/h/m² , 0.42 ± 0.08 AU), Autograft (6.91 ± 1.28 g/h/m² , 0.40 ± 0.08 AU) and healthy mouse skin (6.40 ± 0.43 g/h/m² , 0.35 ± 0.03 AU). Histological results showed that human TESSs and autografts presented better skin structuration and higher expression of cytokeratins.

CONCLUSIONS

This study suggests that human TESS based on fibrin-hyaluronic acid biomaterial could be suitable for clinical application in the treatment of several dermatological pathologies (wound healing).

Spatial configurations and temperature profiles in nonequilibrium steady state of two-species trapped ion systems

We study Coulomb crystals containing two ion species simultaneously confined in radio frequency traps and coupled to different thermal reservoirs located in two separate regions. We use a three-dimensional model to simulate the trapped bicrystal and show in a numerically rigorous manner the effects of the mass dependence of the trapping frequencies on the underlying nonequilibrium dynamics and the temperature profiles. By solving the classical Langevin equations of motion, we obtain the spatial probability densities of the two ion species and the kinetic temperature profiles across the axial direction of the trap in the nonequilibrium steady state. We analyze trapping conditions leading to bicrystals that exhibit ion conformations ranging from a linear chain of alternating ion species to two- and three-dimensional configurations. The results evidence the spatial segregation of the two ion species due to the mass dependence of the trapping frequencies and the increase of ion delocalization for heavier ion species and/or weaker trapping confinements. We also show the correlation between the increase of the temperature gradient in the bulk and this enhancement of ion delocalization through the trap.

Delocalization and heat transport in multidimensional trapped ion systems

We study the connection between heat transport properties of systems coupled to different thermal baths in two separate regions and their underlying nonequilibrium dynamics. We consider classical systems of interacting particles that may exhibit a certain degree of delocalization and whose effective dimensionality can be modified through the controlled variation of a global trapping potential. We focus on Coulomb crystals of trapped ions, which offer a versatile playground to shed light on the role that spatial constraints play on heat transport. We use a three-dimensional model to simulate the trapped ion system and show in a numerically rigorous manner to what extent heat transport properties could be feasibly tuned across the structural phase transitions among the linear, planar zigzag, and helical configurations. By solving the classical Langevin equations of motion, we analyze the steady state spatial distributions of the particles, the temperature profiles, and total heat flux through the various structural phase transitions that the system may experience. The results evidence a clear correlation between the degree of delocalization of the internal ions and the emergence of a nonzero gradient in the temperature profiles. The signatures of the phase transitions in the total heat flux as well as the optimal spatial configuration for heat transport are shown.

Correction to: Similarities and differences in tissue distribution of DLK1 and DLK2 during E16.5 mouse embryogenesis

In the original publication of the article, some symbols in Figure 3 were not correctly aligned with the image.

Absence of Notch1 in murine myeloid cells attenuates the development of experimental autoimmune encephalomyelitis by affecting Th1 and Th17 priming

Inhibition of Notch signalling in T cells attenuates the development of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Growing evidence indicates that myeloid cells are also key players in autoimmune processes. Thus, the present study evaluates the role of the Notch1 receptor in myeloid cells on the progression of myelin oligodendrocyte glycoprotein (MOG)_35-55 -induced EAE, using mice with a myeloid-specific deletion of the Notch1 gene (MyeNotch1KO). We found that EAE progression was less severe in the absence of Notch1 in myeloid cells. Thus, histopathological analysis revealed reduced pathology in the spinal cord of MyeNotch1KO mice, with decreased microglia/astrocyte activation, demyelination and infiltration of CD4⁺ T cells. Moreover, these mice showed lower Th1 and Th17 cell infiltration and expression of IFN-γ and IL-17 mRNA in the spinal cord. Accordingly, splenocytes from MyeNotch1KO mice reactivated in vitro presented reduced Th1 and Th17 activation, and lower expression of IL-12, IL-23, TNF-α, IL-6, and CD86. Moreover, reactivated wild-type splenocytes showed increased Notch1 expression, arguing for a specific involvement of this receptor in autoimmune T cell activation in secondary lymphoid tissues. In summary, our results reveal a key role of the Notch1 receptor in myeloid cells for the initiation and progression of EAE.

The Tetraspanin TSPAN33 Controls TLR-Triggered Macrophage Activation through Modulation of NOTCH Signaling

The involvement of NOTCH signaling in macrophage activation by Toll receptors has been clearly established, but the factors and pathways controlling NOTCH signaling during this process have not been completely delineated yet. We have characterized the role of TSPAN33, a tetraspanin implicated in a disintegrin and metalloproteinase (ADAM) 10 maturation, during macrophage proinflammatory activation. Tspan33 expression increases in response to TLR signaling, including responses triggered by TLR4, TLR3, and TLR2 activation, and it is enhanced by IFN-γ. In this study, we report that induction of Tspan33 expression by TLR and IFN-γ is largely dependent on NOTCH signaling, as its expression is clearly diminished in macrophages lacking Notch1 and Notch2 expression, but it is enhanced after overexpression of a constitutively active intracellular domain of NOTCH1. TSPAN33 is the member of the TspanC8 tetraspanin subgroup more intensely induced during macrophage activation, and its overexpression increases ADAM10, but not ADAM17, maturation. TSPAN33 favors NOTCH processing at the membrane by modulating ADAM10 and/or Presenilin1 activity, thus increasing NOTCH signaling in activated macrophages. Moreover, TSPAN33 modulates TLR-induced proinflammatory gene expression, at least in part, by increasing NF-κB-dependent transcriptional activity. Our results suggest that TSPAN33 represents a new control element in the development of inflammation by macrophages that could constitute a potential therapeutic target.

DLK1 is a novel inflammatory inhibitor which interferes with NOTCH1 signaling in TLR-activated murine macrophages

Delta-like protein 1 (DLK1) is a noncanonical ligand that inhibits NOTCH1 receptor activity and regulates multiple differentiation processes. In macrophages, NOTCH signaling increases TLR-induced expression of key pro-inflammatory mediators. We have investigated the role of DLK1 in macrophage activation and inflammation using Dlk1-deficient mice and Raw 264.7 cells overexpressing Dlk1. In the absence of Dlk1, NOTCH1 expression is increased and the activation of macrophages with TLR3 or TLR4 agonists leads to higher production of IFN-β and other pro-inflammatory cytokines, including TNF-α, IL-12, and IL-23. The expression of key proteins involved in IFN-β signaling, such as IRF3, IRF7, IRF1, or STAT1, as well as cRel, or RelB, which are responsible for the generation of IL-12 and IL-23, is enhanced in Dlk1 KO macrophages. Consistently, Dlk1 KO mice are more sensitive to LPS-induced endotoxic shock. These effects seem to be mediated through the modulation of NOTCH1 signaling. TLR4 activation reduces DLK1 expression, whereas increases NOTCH1 levels. In addition, DLK1 expression diminishes during differentiation of human U937 cells to macrophages. Overall, these results reveal a novel role for DLK1 as a regulator of NOTCH-mediated, pro-inflammatory macrophage activation, which could help to ensure a baseline level preventing constant tissue inflammation.

Characterization of a proximal Sp1 response element in the mouse Dlk2 gene promoter

BACKGROUND

DLK2 is an EGF-like membrane protein, closely related to DLK1, which is involved in adipogenesis. Both proteins interact with the NOTCH1 receptor and are able to modulate its activation. The expression of the gene Dlk2 is coordinated with that of Dlk1 in several tissues and cell lines. Unlike Dlk1, the mouse Dlk2 gene and its locus at chromosome 17 are not fully characterized.

RESULTS

The goal of this work was the characterization of Dlk2 mRNA, as well as the analysis of the mechanisms that control its basal transcription. First, we analyzed the Dlk2 transcripts expressed by several mouse cells lines and tissues, and mapped the transcription start site by 5' Rapid Amplification of cDNA Ends. In silico analysis revealed that Dlk2 possesses a TATA-less promoter containing minimal promoter elements associated with a CpG island, and sequences for Inr and DPE elements. Besides, it possesses six GC-boxes, considered as consensus sites for the transcription factor Sp1. Indeed, we report that Sp1 directly binds to the Dlk2 promoter, activates its transcription, and regulates its level of expression.

CONCLUSIONS

Our results provide the first characterization of Dlk2 transcripts, map the location of the Dlk2 core promoter, and show the role of Sp1 as a key regulator of Dlk2 transcription, providing new insights into the molecular mechanisms that contribute to the expression of the Dlk2 gene.

Cooperation of adenosine with macrophage Toll-4 receptor agonists leads to increased glycolytic flux through the enhanced expression of PFKFB3 gene

Macrophages activated through Toll receptor triggering increase the expression of the A(2A) and A(2B) adenosine receptors. In this study, we show that adenosine receptor activation enhances LPS-induced pfkfb3 expression, resulting in an increase of the key glycolytic allosteric regulator fructose 2,6-bisphosphate and the glycolytic flux. Using shRNA and differential expression of A(2A) and A(2B) receptors, we demonstrate that the A(2A) receptor mediates, in part, the induction of pfkfb3 by LPS, whereas the A(2B) receptor, with lower adenosine affinity, cooperates when high adenosine levels are present. pfkfb3 promoter sequence deletion analysis, site-directed mutagenesis, and inhibition by shRNAs demonstrated that HIF1α is a key transcription factor driving pfkfb3 expression following macrophage activation by LPS, whereas synergic induction of pfkfb3 expression observed with the A(2) receptor agonists seems to depend on Sp1 activity. Furthermore, levels of phospho-AMP kinase also increase, arguing for increased PFKFB3 activity by phosphorylation in long term LPS-activated macrophages. Taken together, our results show that, in macrophages, endogenously generated adenosine cooperates with bacterial components to increase PFKFB3 isozyme activity, resulting in greater fructose 2,6-bisphosphate accumulation. This process enhances the glycolytic flux and favors ATP generation helping to develop and maintain the long term defensive and reparative functions of the macrophages.

Kinetic modelling of passive transport and active efflux of a fluoroquinolone across Caco-2 cells using a compartmental approach in NONMEM

The purpose was to develop a general mathematical model for estimating passive permeability and efflux transport parameters from in vitro cell culture experiments. The procedure is applicable for linear and non-linear transport of drug with time, <10 or >10% of drug transport, negligible or relevant back flow, and would allow the adequate correction in the case of relevant mass balance problems. A compartmental kinetic approach was used and the transport barriers were described quantitatively in terms of apical and basolateral clearances. The method can be applied when sink conditions are not achieved and it allows the evaluation of the location of the transporter and its binding site. In this work it was possible to demonstrate, from a functional point of view, the higher efflux capacity of the TC7 clone and to identify the apical membrane as the main resistance for the xenobiotic transport. This methodology can be extremely useful as a complementary tool for molecular biology approaches in order to establish meaningful hypotheses about transport mechanisms.

Clinical and polygraphic evolution of sleep-related breathing disorders in adolescents

It has been suggested that sleep-related breathing disorders (SRBD) involve a continuum that develops over the course of life. If modifiable factors could be identified, the progression of SRBD could perhaps be addressed early in life. Although some studies have looked at the evolution of SRBD in pre-pubertal children, very few studies obtained data in adolescents. Anthropometric, clinical and polygraphic variables were collected during a 4-yr follow-up study among 148 normal adolescents after initial cross-sectional analysis. From a total of 267 adolescents studied at baseline (mean+/-sd age 14.3+/-2.1 yrs), 148 (55.4%) were followed up for 4 yrs. During follow-up, there were no significant changes in snoring and polygraphic parameters. However, a tendency toward weight gain with centrally distributed fat was observed. Habitual snorers had a significantly higher body mass index and more centrally distributed fat than nonsnorers. Males had a higher snoring prevalence and a higher number of respiratory events than females. Snoring at baseline, male sex and poor academic performance were significant predictors of snoring at follow-up. Snoring tends to persist during adolescence and male sex acts as a risk factor. A relationship between snoring and academic performance was observed. These findings may have implications for long-term management of sleep-related breathing disorders.

Laboratory evaluation of entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae against puparia and adults of Ceratitis capitata (Diptera: Tephritidae)

Laboratory experiments were done to measure the pathogenicity of 10 autochthonous isolates of Beauveria bassiana (Balsamo) Vuill. and of five Metarhizium anisopliae (Metsch.) Sorok. toward puparia and adults of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Although all isolates applied via inoculation of the fungal suspensions on the ventral surface of the abdomen were pathogenic to adults, with mortality rates ranging from 30 to 100% and average survival times (ASTs) from 6.5 to 8.6 d, when C. capitata puparia were immersed in the conidial suspensions, only B. bassiana Bb-1333 and EABb 01/103-Su and M. anisopliae EAMa 01/58-Su isolates caused >50% mortality of puparia. In a second series of bioassays conducted on five selected isolates, adults were sprayed with four 10-fold concentrations ranging from 1.0 x 10(5) to 1.0 x 10(8) colony-forming units (cfu)/ml. The median lethal concentrations (LC50) of the four most virulent isolates ranged from 4.9 x 10(5) to 2.0 x 10(6) cfu/ml with estimated time to kill 50% of the insects ranging from 4.6 to 5.3 d. The effect of a sublethal dose (ca. LD50) of either B. bassiana EABb 01/103-Su or M. anisopliae EAMa 01/58-Su isolate was studied by reciprocal crossing. Treatment with B. bassiana reduced fecundity and fertility at 6, 8, and 10 d after treatment, with fecundity and fertility reductions ranging from 20.0 to 71.2% and from 33.6 to 60.0%, respectively. These reductions occurred in pairing combinations of treated females with either treated or nontreated males. M. anisopliae was more effective in reducing fecundity and fertility at 6 d after treatment, with the reduction varying from 58.4 to 72.1% and from 28.6 to 45.9%, respectively. In addition, the first oviposition was significantly delayed for 1 d in females treated by either fungal species. The above-mentioned five selected isolates were assayed against C. capitata puparia treated as late third instars in sterilized soil at 25'C under three moisture conditions (-0.1, -0.01, and -0.0055 MPa). At -0.01 MPa, all isolates were low pathogenic to C. capitata puparia, whereas significant differences in the puparia mortality occurred between isolates at -0.1 and -0.0055 MPa. The highest pupal mortalities ranged from 52.5 to 70.0%, as a function of soil moisture and were caused by EAMa 01/58-Su and Bb-1333 isolates.

[Study of unmatched cases and controls: hyperhomocysteinaemia and chronic ischaemic cardiopathy]

OBJECTIVE

To evaluate the extent of the association between hyperhomocysteinaemia and chronic ischaemic heart disease.

DESIGN

Unmatched, case-control (1:3) study.

SETTING

Pintores Health Centre, Area 10, Primary Care, Madrid, Spain.

PARTICIPANTS

Patients of the health centre over 35 with chronic ischaemic heart disease or without it.

METHOD

Consecutive, non-randomized sample. Analysis of cases and controls with chi2 test and odds ratio (OR). The quantitative variables were analysed with the Student's t test.

RESULTS

The 76.32% (87/114) of cases had 2 or more cardiovascular risk factors versus 33.56% (99/265) in the control group (P<.0001). Average homocysteinaemia was 10.07 micromol/L (SD, 3.64) in the control group; and 12.74 (SD, 4.59) in the cases group. The difference between the averages (2.67 micromol/L; 95% CI, 1.82-3.52) was significant (P<.001). The difference (16.07%; 95% CI, 6.91-25.23) in hyperhomocysteinaemia (> or =15 micromol/L) between cases (28.95%, 33/114) and controls (12.88%, 38/295) was significant (P=.0001), with an association between hyperhomocysteinaemia and chronic ischaemic heart disease (OR=2.76; 95% CI, 1.62-4.68). This association increased (OR=3.26; 95% CI, 2.07-5.13) when hyperhomocysteinaemia was taken as > or =12 micromol/L, with a significant difference of 27% (95% CI, 16.59-37.41) (P<.0001) between cases (51.75%, 59/114) and controls (24.75%, 73/295).

CONCLUSIONS

The risk factor of hyperhomocysteinaemia > or =15 micromol/L was significantly associated (OR=2.76) with chronic ischaemic heart disease. This association was greater (OR=3.26) when hyperhomocysteinaemia was taken as > or =12 micromol/L.

Pharmacokinetics, bioavailability and absorption of flumequine in the rat

The study demonstrates that the oral extent of bioavailability of flumequine in the rat, relative to the intravenous injection, is complete (0.94 +/- 0.04) and not significantly different from that found by the intraduodenal route (0.95 +/- 0.04). The rate of oral bioavailability, however, is slow (ka = 1.20 +/- 0.07 h-1; Tmax = 2.0 h), but enough to maintain plasma levels above the minimal inhibitory concentration of the most common pathogens for an extended period of time (about 10 h). The reason for the oral absorption slowness could be a slow gastric emptying, an adsorption to the gastric mucosae, a precipitation in the gastric medium or any other feature concerning the stomach as the intraduodenal administration is very quick (kid = 38.1 +/- 4.7 h-1; Tmax = 0.05 h). A possible precipitation of flumequine cannot be discarded as the solubility of flumequine is very low in the pH range of 3 to 6 (mean pH values for rat stomach and rat intestine, respectively; T.T. Kararli, Biopharm. Drug Dispos. 16 (1995) 351-380). Flumequine was shown to be not substantially excreted in bile (2-3% of the dose). Surprisingly, plasma levels and AUC values found for animals with interrupted bile flow always surpass those found for animals with enterohepatic circulation. This could be due to experimental model features, which might bias plasmatic flumequine concentrations if the homeostatic equilibrium of the animal is not completely restored due to the volume reduction induced by biliary extraction.