Lung kinetics of radioactive iodobenzyl-propanediamine as an index of lung metabolic function.

Lung metabolism of endogenous amines has been experimentally documented. We studied lung kinetics of radioiodinated N-N-N-trimethyl-N'-(2-hydroxy-3-methyl-5-iodobenzyl)-l,3-propanediamine (HIPDM), a synthetic compound chemically related to endogenous amines. In 10 healthy non smokers we recorded by a computerized gamma camera, time/activity curves over the lung fields up to 3 hrs from HIPDM i.v. injection. Multiexponential analysis of time/activity curves showed that HIPDM lung kinetics is described by three exponential components. The first two may reflect early phenomena of tracer redistribution and are completed by:40 min. The third component is characterized by a shallow, monoexponential downslope, with a mean time (t) of 6.4±0.8(SD) hrs, compatible with a metabolic process of the first order. This latter component was also observed in bits in which HIPDM lung kinetics was assessed both in vivo, by external counting, and in vitro by measuring radioactivity in lung tiomogenates at various times after i.v. injection. The calculated t of the slow monoexponential component, 7.0+/-1.3 hrs, is not significantly different from that observed in the humans. Preliminary studies in man indicate that HIPDM lung kinetics is significantly delayed in asymptomatic smokers (n=10; t: 12.1±1.7 hrs) and, to a greater extent, in patients with injury lung edema (n=4; t: 19.6^.5 hrs). Hence, both smoke exposure and injury to the lung microcirculation may impair HIPDM lung metabolism. External recording of HIPDM time/activity curves may therefore provide an index of lung metabolic dysfunction. Rabbit can be used as a model to evaluate HIPIDM metabolism in experimentally induced lung disease.