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PARTICIPATION OF THE SKIN IN THE TRANSPORT MECHANISM

Title.

Migration of the Tc-99m subcutaneous injection and correlation with cutaneous structures: an experimental study in dogs.

Background.

It has been shown that Tc-99m is transported subcutaneously by a previously non-described mechanism (see page 84). It was not known what mechanism transported it and through what pathways. In this situation, the concept was to damage different structures, beginning through the skin, to observe which of them, upon being damaged, affected the transport mechanism.

Objective.

To determine the skin's participation in the transport mechanism of Tc-99m.

Methodology.

72 male beagles, between 19 and 36 months old, were anesthetized and 200 to 250 cmCI of Tc-99m were injected in a point on the back of the wrist. The specific point was defined as being of lower electrical resistance than that of the ear. Only one experiment was made on each dog.

In different experiments, a cut was made in the back or front paw, on the same side or on the opposite side as that in which the isotope was injected, and before or after the injection. All of the cuts made on the front paws intersected the migration pathway. Finally, a skin flap was extracted from the migration pathway and another from the opposite side paw.

Participants, along with the Foundation's Science Department.

Departments of Nuclear Medicine of the Hospital Clínico of Barcelona, Morphological Sciences at the Central University of Barcelona (Medical School), and Animal Surgery at the Autonomous University of Barcelona (Veterinary School).

Funded entirely by the Kovacs Foundation.

Results.

Published in the European Journal of Nuclear Medicine (Kovacs FM, Gotzens V, García A, et al. Kinetics of hypodermically injected technetium-99m and correlation with cutaneous structures: an experimental study in dogs. Eur J Nucl Med 1993; 20:585-90).

To summarize, they indicate that the skin cut in the back paws did not affect the migration pathway, but the cut in the front paws did. When the cut was made before the injection of the isotope, in either of the two front paws, the isotope did not migrate-that is to say, it was not transported--. When the cut was made after the injection of the isotope, when its initial migration had already been observed:

1. When the cut was made in the opposite paw to the one injected, the migration was stopped.

2. When the cut was made in the same paw as the isotope injection, the previously observed radioactive activity in the migration pathway disappeared.

Por último, no se observó actividad radioactiva en el colgajo procedente del trayecto de migración ni en el procedente de la extremidad contralateral.

Finally, radioactive activity was not observed in the flap from the migration pathway nor in that from the opposite side paw.
In short, these results indicate that the isotope does not migrate through the skin, but that the skin covering the migration pathway and the corresponding territory in the opposite extremity has to be unharmed for the isotope to be transported.

On the other hand, the results also confirm that no previously known corporal system is responsible for this transport: these characteristics do not pertain to lymphatic, nerve or vascular transport.