Evaluation of the lung uptake of iodine-131 HIPDM by the single-pass multiple indicator dilution technique in a rabbit model.

The first-pass lung uptake of [131I]HIPDM was studied in a rabbit model using a conventional single-pass multiple indicator dilution (SPMID) technique with [99mTc]HSA as the intravascular marker. Lung extraction of [131I]HIPDM determined by the SPMID method was saturable, decreasing from 89.5 +/- 5.8% (mean +/- s.d., n = 4) at 4 nmol kg-1 to 63.8 +/- 6.2% at 1.5 X 10(4) nmol kg-1 relative to the intravascular tracer. The first-pass extraction of [131I]HIPDM derived from gamma-camera emission imaging data correlated well (R = 0.834) with simultaneously derived SPMID data. The extraction efficiencies were 94.4 +/- 3.3 and 87.9 +/- 3.2 at 200 nmol kg-1 and 68.0 +/- 6.2 and 64.0 +/- 10.7 at 1 X 10(4) nmol kg-1 (n = 4) for the SPMID and gamma-camera methods, respectively. Analysis of the lung arterial effluent blood indicated that no appreciable de-iodination or metabolism of [131I]HIPDM, within the limits of detection, occurred during the first pulmonary transit.