A method for in vivo diffusion tracer studies combining perfusion fixation with intravenous tracer injection

Summary A method permitting exact time studies in diffusion tracer experiments in vivo is described. The method consist in application of perfusion fixation via the aorta abdominalis after the injection of the tracer substance. As the animal can be prepared for perfusion before the tracer is injected, time accuracy is in the order of a few seconds. Some applications of the method are demonstrated. A further advantage of the method is good tissue preservation. This perfusion technique is also recommended for study when exact timing is necessary, for example in autoradiography.Supported by grants from the Fonds national suisse de la Recherche scientifique, Berne, Switzerland. We wish to thank M. P. Detraz for technical assistance.     

On the application of compartmental models to radioactive tracer kinetic studies of in vivo protein turnover in animals

A mathematical framework is presented for unifying and extending the various compartmental models and formulae used to calculate fractional protein synthesis and degradation rates in animals from data obtained by infusing labelled amino acids. It is shown how the various schemes can be derived as special cases of the product-precursor model or some three-pool variant. Three-compartment representations, which circumvent the need to measure the specific radioactivity of the precursor pool, are proposed. The mathematical solutions are generally presented in a form that is amenable to parameter estimation by non-linear least squares. The problems of measuring the true precursor pool for protein synthesis are addressed, and theoretical consideration is given to assaying aminoacyl-tRNA.     

A cage for the collection of excreta from individual mice in radioactive tracer studies.

A simple and inexpensive unit for the collection of excreta from individual mice was designed. The results of experiments in which counts of collected radioactive excreta were made closely approximated those previously obtained using a whole-body gamma counter.     

Direct preparation of radioactive fullerenes as a tracer for applications

The C₆₀ and C₇₀ fullerenes were irradiated by high-energy γ-rays and charged particles. The irradiated samples were dissolved in CS₂ and/or toluene and filtered to remove insoluble by-products. Finally, radioactive fullerenes and products labeled with¹¹C or¹³N were isolated and detected in the liquid phase by radiochromatography. It was found that (1) not only¹¹C or¹³N radioactive monomer fullerenes but also their dimers (trimers and, possibly, tetramers) were produced by recoil implantation process following nuclear reaction and (2) the radioactive fullerene labeled with¹¹C yields has led to high yields.     

Arsenic translocation in rice investigated using radioactive 73As tracer

Plant and Soil - Excessive accumulation of arsenic (As) in rice (Oryza sativa L.) may pose a health risk to rice consumers. Long-distance transport of As within plant tissues is not well...     

Length dependence in reassociation kinetics of radioactive tracer DNA.

The reassociation kinetics have been measured for radioactive Escherichia coli DNAs (tracers) of various average single-strand lengths reassociated alone and in the presence of excess unlabeled DNA (driver) of two different average lengths. Hydroxylapatite binding was used to follow the reaction time course. The length-dependence of the rate constant determined in the tracer self-reassociation reactions is in agreement with the square-root dependence previously determined (Wetmur, J. G., & Davisond, N. (1968) J. Mol. Biol. 31, 349-370) using optical methods to follow the time course. However, for the driver-tracer reactions, where the radioactive DNA reassociates largely with DNA of a different average length, the dependence of the rate constant upon average tracer length is increased and approaches an L to the first power dependence. In 0.18 M Na+, the variation of the rate constant for tracer reassociation with the lengths of the reassociating strands has been shown to fit the simple equation k = (9.0077).(L T 0.55 + 1/L D 0.55), where k is the observed rate constant in L mol-1 s-1 and L(T)and L(D) are the weight average tracer and driver lengths, respectively, in nucleotides. This dependence suggests that the rate of nucleation of two free strands is proportional to the sum of the reciprocals of the hydrodynamic radii of the two strands.     

Schistosoma mansoni: tracer studies in mice

Mice with patent Schistosoma mansoni infections were injected via the tail vein with peroxidase and Thorotrast, and the ingestion of these tracers by the worms was followed over time. Both tracers are found initially in the crypts of the dorsal tegument of the male; however, the disappearance of the peroxidatic activity from the crypts, presumably by digestion of the peroxidase, occurs prior to the disappearance of the Thorotrast. Only Thorotrast appears in the cecal lumen, and the amount is greater in the female than in the male. Little tracer is ever found between the pair in the gynecophoric canal, and no tracer was ever found in the cytoplasm of the worms. These results suggest that while the tegumental and cecal surfaces are cytoarchitecturally identical in both sexes, they may in fact exhibit functional specializations.     

TFLUX: a general purpose program for the interpretation of radioactive tracer experiments.

TFLUX is a computer program which simulates radioactive tracer experiments using intact cells under steady-state conditions. It is designed for the naive computer user to use, providing English-like input. An example is described in which compartmentation and flux through the citric acid cycle in Dictyostelium discoideum are simulated.     

Horseradish peroxidase as a tracer for capillary permeability studies

The permeability of capillaries was investigated utilizing an in vivo injection of horseradish peroxidase (HRP) and an in situ perfusion of a balanced salt solution containing HRP and lanthanum chloride. In the continuous capillaries of heart and muscle, HRP diffuses mainly through intercellular junctions, while in testicular capillaries, the transport is via micropinocytotic vesicles. The diffusion and micropinocytotic transport of HRP was demonstrated in both directions, i.e. from the capillary lumen to the interstitium and vice versa. Lanthanum can be used as a bidirectional inhibitor of micropinocytosis. The transport of HRP is then almost completely hindered in testicular capillaries. In heart muscle, the effect on HRP transport is not significant, due to second transport pathway, i.e. intercellular cleft passage.