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

The distribution of systematically injected In-113m (t1/2 = 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 6 h 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 second probe directed toward a control area is needed.