Some applications of the Indium-113m-transferrin technique for gamma-radiation detection of microvascular effects of serotonin and ischemia

Summary

The distribution of systematically injected In-113m (t _1/2 = 100 min) in organs of the rat was analyzed, and the use of the isotope for in vivo and in vitro gamma-radiation detection studies of blood plasma protein extravasation was demonstrated in skin, muscle, and tumor.

In-113m was slowly excreted from rats. One to 6h after injection the blood held 3% and 2%, respectively, of injected radioactivity/g tissue wet weight; skin and muscle held 0.1%–0.2%/g; liver, colon, and spleen held approximately 1%/g; lungs 1.5%–1.3%/g and kidneys 2.8%–3.3%/g.

Scintillation camera technique revealed 40%–80% extraaccumulation of In-113m in a control extremity upon local administration of serotonin and 20%–40% in an extremity with a transplanted tumor, thus indicating a lower effect of serotonin in tumor microvascular circulation than in muscle and skin.

In vitro detection of In-113m radiation by a well-counter in dissected tissues showed no effects of serotonin in the tumor and a four- to five-fold increase of radioactivity in muscle and skin, thus confirming blood protein extravasation upon serotonin treatment in these tissues.

External analyses of In-113m in the vascular system using one miniaturized probe directed toward an area of interest showed that the method was too sensitive to movements of the animal, and a second probe directed toward a control area is needed.