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)