RESUMEN
This paper presents a model describing the diffusion of water and contrast agent (CA) in hollow fibre modules (HFM), which is able to calculate the contribution of water molecular exchange to the parameters resulting from dynamic R(1) relaxation data. To acquire these data, the intra-fibre volume of the HFM initially filled with pure water was perfused with a CA solution of constant concentration C(0). The relaxation rate R(1e)(t) time course was measured assuming fast water molecular exchange, with a saturation-recovery multi-gradient-echo snapshot sequence. These data led to uncorrected (uc) water exchange estimations of the constant k(CA_uc) characterizing the CA R(1e)(t) kinetics and of the intra-fibre volume fraction V(in_uc) of the HFM. The model, which assumes diffusion-controlled process and the absence of interaction of CA with the fibre membrane, led to the corresponding theoretical values for corrected water exchange k(CA) and V(in). k(CA_uc) was always slightly larger than k(CA) and independent of C(0). V(in_uc) was always much smaller than V(in) and depended strongly on C(0). Furthermore, V(in) was found to be very similar to the real intra-fibre volume fraction as determined directly from high-resolution MRI and specifications given by the supplier, thus confirming the validity of our model. It is shown that k(CA_uc) characterizing every CA diffusing without interaction with the membrane depends linearly on its diffusion coefficient in water D(s_CA). The experimental results suggest that interactions of Dotarem and P806 with the HFM membrane are not significant. This is also the case for the smaller and neutral molecule water, validating all the calculations involved in this work. For the largest CAs, experiments suggest that sterical effects dominate their permeability and that D(s_CA) rather than their molecular weight defines HFM membrane cut-off. However, if other interactions are also important, a multi-parameter function rather than a single value is expected to define this cut-off.
Asunto(s)
Imagen por Resonancia Magnética/instrumentación , Imagen por Resonancia Magnética/métodos , Membranas Artificiales , Reactores Biológicos , Medios de Contraste/química , Difusión , Cinética , Peso Molecular , Agua/químicaRESUMEN
A double-delay SR-MGE-SNAP sequence allowing simultaneous T1 and T2* measurement was developed for integrating arterial input function (AIF) measurement into DCE MRI. Implemented on a 4.7-T animal MR system, this technique was applied to mice with colorectal tumor xenografts. AIF, measured in the mouse heart, was modeled by a bi-exponential function, whereas tumor K(trans) and v(e) parameter maps were obtained from analysis with a two- compartment model using an individually measured AIF. AIF analysis of T2*-corrected data yielded A1 = 9.2 +/- 4.3 kg/l, A(2) = 4.2 +/- 0.8 kg/l, m1 = 2.3 +/- 1.1 min(-1), and m2 = 0.05 +/- 0.02 min(-1). The mean initial plasma concentration C ( p )(t = 0) = 8.0 +/- 2.7 mM was compatible with estimated 8.6 mM. Without T2*-correction distribution phase parameters A1, m1, and C(p)(t = 0) were underestimated. In tumors, neglect of T2* effects yielded mean K(trans) values which were reduced by 14% (P < 0.05), whereas v(e) showed only a slight non-significant reduction. Simultaneous measurement of DeltaR1 and DeltaR2* studied in highly and poorly vascularized and (pre-)necrotic tumor regions revealed complementary behavior of both parameters with respect to vascular properties. In conclusion, the presented measurement technique is a promising tool for dynamic MRI applications studied in animal models at high field strengths and/or with CA of high relaxivities, as it combines classical DCE MRI integrating AIF assessment with dynamic T2* measurement.
Asunto(s)
Neoplasias Colorrectales/patología , Imagen por Resonancia Magnética/métodos , Animales , Modelos Animales de Enfermedad , Corazón/anatomía & histología , Humanos , Ratones , Ratones Desnudos , Miocardio/patología , NecrosisRESUMEN
We present experimental MRI protocols at 4.7 T for quantitative determination of the Dotarem distribution volume in isolated perfused rat liver. The procedures involved either constant contrast agent (CA) concentration or bolus administration conditions. R1 and R2* effects of the CA in liver and perfusate were measured using gradient echo fast imaging (GEFI) experiments by varying either the excitation angle or the echo time. CA concentrations in liver and perfusate were also measured after MRI by inductively coupled plasma atomic emission spectroscopy, in order to determine in situ relaxivities in the perfusate (r1=4.2 +/- 0.1 s(-1) mm(-1), r2*=17 +/- 2 s(-1) mm(-1)) and in the liver (r1=7.2 +/- 0.2 s(-1) mm(-1), r2*=99 +/- 5 s(-1) mm(-1)). When CA concentrations were estimated from R1 measurements and r1, the CA distribution volume estimations in liver resulting from bolus (0.31 +/- 0.01) and stationary (0.32 +/- 0.05) experiments were not significantly different. In contrast, after a bolus, CA concentrations derived from R2* and r2* were overestimated in liver and even more in perfusate. However, with R1 and R2* being measured before CA bolus administration, zero echo time signal intensities computed from multiple TE measurements during multiple boli yielded good estimations of R1 and thus correct CA concentrations in liver and in perfusate. Under these conditions, a single multi-echo GEFI acquisition should be sufficient to determine the concentration-time curves. Consequently, this protocol should be appropriate to rapidly estimate the distribution volume in vivo when multiple boli have to be avoided.
Asunto(s)
Algoritmos , Interpretación de Imagen Asistida por Computador/métodos , Circulación Hepática/fisiología , Pruebas de Función Hepática/métodos , Hígado/irrigación sanguínea , Hígado/citología , Imagen por Resonancia Magnética/métodos , Meglumina , Compuestos Organometálicos , Animales , Medios de Contraste/farmacocinética , Técnicas de Dilución del Indicador , Hígado/metabolismo , Masculino , Meglumina/farmacocinética , Tasa de Depuración Metabólica , Técnicas de Cultivo de Órganos , Compuestos Organometálicos/farmacocinética , Ratas , Ratas Wistar , Sensibilidad y Especificidad , Distribución TisularRESUMEN
This paper describes multinuclear NMR investigations on the isolated perfused mouse liver to optimize its recovery after cold preservation and normothermic reperfusion. The recovery of livers from fed is better than that from 24 h fasted animals. This better recovery is not due to a higher glycogen content before cold preservation. The recovery of livers from fasted animals is specifically enhanced by the presence of 8 mM alanine in the rinsing solution after cold preservation and in the perfusate of reperfusion. This property is not due to the ability of alanine to compensate for the lack of endogenous substrates since the amount, before cold preservation, of these substrates, is not significantly different in livers from fed and fasted animals. Furthermore, the beneficial effect of alanine is not due to an enhancement of the pyruvate dehydrogenase (PDH) activity in livers from fasted animals. In fact these livers have indeed a smaller PDH activity than the livers from fed animals but dichloroacetate, a known PDH activator has a rather deleterious effect on the recovery of fed and fasted livers. Furthermore alanine protects the fasted livers against this effect. So the beneficial effect of alanine should be due to other causes. Furthermore, we have found on a parallel model of rat isolated perfused liver, that the recovery of steatotic livers which is lower than that of normal fed livers is enhanced by a known vasodilator, pentoxifylin but not by alanine. So alanine does not either play its role through its action on microcirculation. The interaction of alanine with some membrane sodium transporters like that already reported for another protective aminoacid, glycine, is thus possible. A novel NMR method of (23)Na observation in living cells or organs should be of great interest to investigate this hypothesis.
Asunto(s)
Criopreservación/métodos , Ayuno/fisiología , Cetona Oxidorreductasas/metabolismo , Hígado/metabolismo , Resonancia Magnética Nuclear Biomolecular/métodos , Alanina/administración & dosificación , Alanina/farmacología , Animales , Isótopos de Carbono , Ácido Dicloroacético/farmacología , Activación Enzimática/efectos de los fármacos , Glucógeno Hepático/metabolismo , Masculino , Ratones , Microcirculación , Perfusión , Recuperación de la Función/fisiología , Triglicéridos/metabolismoRESUMEN
BACKGROUND: The deleterious effect of steatosis on transplanted livers is mainly related to a microcirculation impairment. We investigated the effect of preservation duration on the recovery of isolated perfused rat steatotic livers and tested the effect of pentoxifylline (PTX), known to have a beneficial effect on hepatic microcirculation. MATERIALS AND METHODS: Fatty rat livers were obtained using a diet able to induce an 80% to 100% microvesicular steatosis within 7 days. We studied the effect of the duration of preservation (12 hr, 18 hr, and 24 hr) on fatty and normal isolated perfused rat liver. PTX was added to University of Wisconsin solution during cold storage (30 mM/kg of weight) and at reperfusion (3 mM) (n=5 livers in each group). Lactate dehydrogenase, aspartate aminotransferase, alanine aminotransferase, bile production, and vascular resistance were evaluated. The liver injury at the end of perfusion was assessed by optical and electron microscopy. RESULTS: For a 24-hr preservation period, fatty livers demonstrated increased enzymatic release (aspartate aminotransferase: 42+/-16 vs. 17+/-5 IU/L/g of liver, P<0.005; alanine aminotransferase: 32+/-13 vs. 13+/-3 IU/L/g of liver, P<0.005; lactate dehydrogenase: 1,207+/-497 vs. 291+/-195 IU/L/g of liver, P<0.001). Vascular resistance (0.32 vs. 0.15 cm H(2)O/min/mL, P<0.0005) and bile output (67+/-24 vs. 141+/-61 mg/g of liver, P<0.05) were decreased. Peliosis appeared after an 18-hr preservation period for fatty livers compared with a 24-hr preservation period for controls. All these negative effects were suppressed by PTX. CONCLUSION: Diffuse microvesicular steatosis became deleterious only after long preservation times (24 hr). PTX prevented this effect.
Asunto(s)
Hígado Graso/tratamiento farmacológico , Depuradores de Radicales Libres/uso terapéutico , Isquemia/fisiopatología , Hígado , Pentoxifilina/farmacología , Adenosina , Alopurinol , Animales , Hígado Graso/patología , Glutatión , Insulina , Hígado/efectos de los fármacos , Hígado/patología , Hígado/ultraestructura , Circulación Hepática , Pruebas de Función Hepática , Masculino , Preservación de Órganos/métodos , Soluciones Preservantes de Órganos , Rafinosa , Ratas , Ratas Wistar , Factores de TiempoRESUMEN
The effect of donor nutritional status on hepatic function recovery after cold ischemia is still debated. We demonstrated previously that a 48-h fast diminished the survival rate of liver-transplanted rats and that the deleterious effect of fasting was prevented by infusion of alanine to the recipient at reperfusion. Whether the duration of fasting influenced the protective effect of alanine and whether this effect was metabolic were not known, and the elucidation of these questions is the aim of this study. The effect on hepatic function recovery of fasting periods of 24 h, 48 h and 72 h prior to cold ischemia were studied in a model of isolated, perfused rat liver. After a cold-ischemic time of 24 h in University of Wisconsin (UW) solution at 4 degrees C, livers were reperfused for 3 h. The combined effect of alanine (8 mM) infusion at liver reperfusion was evaluated for each prior fasting period. The addition of pyruvate (8 mM), a metabolic intermediary of alanine, was only tested in the 72-h fasting group. The evaluation criteria were: liver weight after reperfusion, release of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) in the perfusate, bile production, vascular resistance and liver histology after reperfusion. The enzyme release at reperfusion was significantly higher when livers were harvested from rats submitted to a 48-h fast (ALT) or a 72-h fast (ALT, AST, LDH), as compared to those from fed rats. Vascular resistance was increased in 72-h fasted livers. An addition of alanine (8 mM) at reperfusion lowered the release of AST, ALT and LDH. This effect was more obvious when the fasting duration was increased. By contrast, the addition of pyruvate at reperfusion did not improve the recovery of livers submitted to a 72-h fasting period before preservation. A long fasting period is deleterious as compared to feeding; however, this effect can be compensated by infusion of alanine at reperfusion. The mechanism involved is not metabolic. In a clinical setting, the infusion of alanine to the recipient at reperfusion may be a convenient way to compensate for donor undernutrition, especially after a long stay in an intensive care unit.