A theoretical four-compartment model to evaluate separate kidney technetium-99m-MAG3 kinetics in humans.

BACKGROUND: Pharmacokinetic modeling based on compartmentalization has provided a valuable tool to assess the clearance patterns of various glomerular and tubular agents. However, no models have been proposed thus far that combine vascular data and imaging data in order to gain a deeper knowledge on renal pathophysiology, and to obtain more diagnostic information of clinical relevance. To this aim, we propose a four-pool model for the evaluation of separate renal function. METHODS: In a group of ten normal volunteers and twenty patients with various renal diseases, we tested the four-pool model based on the identification of the two kidneys as two distinct pools. This approach made it possible to integrate the separate kidney contributions deriving from in vivo imaging data, and allows the researcher to quantitate many parameters specific to each kidney. RESULTS: The parameters TERR, TERL, MRTR, MRTL, vR, vL, k3R-1, K3L-1 permit the normal from abnormal states of renal function to be differentiated, as well as monolateral from bilateral renal disease to be separated within the abnormal function group. CONCLUSIONS: The proposed approach combines the advantages of plasma clearance methods with those derived by gamma-camera imaging, and makes it possible to quantitate the differential renal function. This feature may be clinically relevant in renal transplant donors, where full knowledge of renal pathophysiology could guide the procedure.

Simultaneous estimation of glomerular filtration rate and renal plasma flow.

UNLABELLED: Comparing the measurements of both glomerular filtration (GFR) and tubular excretion rates [TER(MAG3)] by multi-sample and single-sample methods has been performed after a single bolus injection of 3.7 MBq 51Cr-EDTA plus 37 MBq 99mTc-MAG3. METHODS: We studied 17 healthy volunteers and 28 patients with a wide range of renal function. For each plasma clearence curve, nine plasma samples were drawn at intervals from 10 to 240 min after injection of tracers. When comparing individual values for GFR and TER (MAG3) from the tracer dilution spaces (VD) with those derived from the analysis of the entire plasma disappearance curves of two radiopharmaceuticals, a good linear correlation appears (r = 0.96). RESULTS: We found that the nadir-error (Sy,x) for predicted GFR occurs at 180 min (11.0 ml/min/1.73 m2), while the nadir-error for predicted TER (MAG3) is reached at 90 min (26.4 ml/min/1.73 m2). CONCLUSION: In the computation of GFR and TER (MAG3) with a single-sample method, it appears that the mean residence time (t) for each tracer represents the optimum plasma sampling time. Our results suggest that the single injection of 51Cr-EDTA and 99mTc-MAG3 followed by blood sampling twice permits accurate simultaneous estimation of GFR and TER (MAG3) and, after correction of the latter kinetic parameter, effective renal plasma flow.

A theoretical five-pool model to evaluate triiodothyronine distribution and metabolism in healthy subjects.

We have examined the in vivo production, distribution, metabolism, and excretion of radiolabeled triiodothyronine (T3) in eight normal humans using a new five-pool mammillary model which includes four extravascular pools to represent liver, kidney, skeletal muscle, and all other unquantified tissues. Trace amounts of [125I]T3 and [131I]T3 were injected and plasma, stool and urine samples and external counting of liver, kidney, and thigh were drawn following bolus injection of radiolabeled T3. Our results indicate that the skeletal muscle pool represents the largest pool in our system, being 42% of the total-body pool size of the hormone (Qtot = 0.52 +/- 10% [CV] micrograms/kg body weight [BW]). The plasma pool QA (0.090 +/- 9% [CV] micrograms/kg BW) contains approximately 17% of Qtot, while the size of the unquantified tissue pool QE (0.150 +/- 16% [CV] micrograms/kg BW) is approximately 29% of Qtot. Furthermore, the size of liver pool QB and the size of kidney pool QC are about 10% and 2%, respectively, of Qtot. The rate of T3 metabolized in the skeletal muscle pool and in the unquantified composite tissue pool, as a sum, represents approximately 53% of the plasma appearance rate of the hormone (PAR3), while the rate of T3 metabolized in the liver and kidney pools represents 27% and 3% of PAR3, respectively. The rate of T3 excreted via feces and urine, as a sum, accounts for about 20% of PAR3.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of circulating immune complexes in hepatitis by means of a new method employing 125i-antibody. circulating immune complexes in hepatitis.

A new RIA method for the detection of circulating immune complexes and antibodies arising in the course of viral hepatitis is described. It involves the use of 125I-labeled antibodies and foresees the possibility of employing immune complex-coated polypropylene tubes. This simple and sensitive procedure takes into account the possibility that the immune complexes may be absorbed by the surface of polypropylene tubes during the period in which the serum remains there.