Pertechnetate distribution in man after intravenous infusion: a compartmental model.

Using a primed infusion technique, distribution of pertechnetate was monitored in normal volunteer subjects over an 8-hr period. Two groups of subjects were studied, during hours 0-4 (n = 8) and hours 4-8 (n = 7), respectively, of the infusion. At 6.5 hr a large dose of NaI (1000 mg) was administered intravenously to the second group. Plasma, salivary, and urinary radioactivities were assayed, and external counts were made of radioactivities over the neck, thigh, and right upper abdomen. A kinetic model was developed for pertechnetate based upon the distribution data, the iodide perturbation, and known physiology for pertechnetate and iodide. The model has three major subsystems: (1) the thyroid trap; (2) a whole-body distribution, containing plasma and two extravascular compartments; and (3) the gastrointestinal tract, including the salivary, stomach (including upper small intestine), and two lower intestinal compartments. One of the latter, which turns over very slowly, is believed to represent bowel wall. The large NaI dose markedly reduced transport into compartments of the thyroid trap, the saliva, and the stomach and small intestine. This study shows that, in most respects, pertechnetate is distributed qualitatively but not quantitatively like iodide but that, unlike iodide, large bowel distribution plays an important role, especially in long-term studies.