Biodistribution of [111In-DTPA-D-Phe1]-octreotide in dogs: uptake in the stomach and intestines but not in the spleen points towards interspecies differences.

The purpose of the present study was to establish the tissue distribution in abdominal organs and the excretion of radioactivity after intravenous administration of [(111)In-DTPA-D-Phe(1)]-octreotide in healthy dogs. In five Beagle dogs computed tomography and single photon emission computed tomography (SPECT) at 24 h after injection of [(111)In-DTPA-D-Phe(1)]-octreotide revealed accumulation of radioactivity in the kidneys, gall bladder, gastric fundus and cardia, intestinal tract, but not in the spleen. These findings were confirmed by in vitro scintigraphy of single abdominal organs. This also demonstrated accumulation of radioactivity in the pancreas and located the radioactivity in the gastrointestinal tract primarily in the wall itself. In vitro autoradiography with (125)I-[Tyr(3)]-octreotide on tissue samples in two dogs revealed sst receptors in the medullary part of the kidney, the basal two-thirds of the gastric mucosa of the cardia and fundus, Peyer's patches and neural plexus of the gastrointestinal tract. No sst receptors were demonstrated in the liver, spleen, and pancreas. These results differ to findings in man, where there is uptake in the spleen but not in the stomach, most likely caused by interspecies variations in sst receptor subtype expression.