Evaluation of labeling procedures and in vivo stability of 99mTc-red blood cells.

Stable labeling of red blood cells (RBCs) with 99mTc, in yields of about 66%, was achieved by using stannous chloride as a reducing agent. In a study of 12 patients, the stability of technetium-labeled RBCs in the circulation varied significantly among individuals, but the average biologic half-life of the labeled cells was 16.8 hr. Although the labeling yield was lower when the labeling was carried out without EDTA with the addition of stannous chloride after the pertechnetate, this sequence appears to be the best for labeling RBCs for use in obtaining images of the blood pool or the cardiovascular system because of the increased viability of the RBCs.

Potential use of ascorbic acid as a pituitary and adrenal scintigraphic agent.

The distribution of intravenously administered 14C-ascorbic acid (AA) into various tissues of the dog, and the effect of dexamethasone and ACTH administration on the AA distribution was studied. As a function of time, the differences of 14C-AA distribution between adrenal and surrounding organs become greater, and 24 hours after the administration of the dose, the adrenal to liver ratio, as well as adrenal to kidney, is about 10:1. Also concentration of AA in the pituitary showed a gradual increase and reached its peak between 24 and 48 hours. Dexamethasone administration lowered significantly the uptake of 14C-AA by the adrenals, but did not affect the uptake by the pituitary. Three consecutive days administration of ACTH did not affect the uptake of the drug by either glands, but one single dose of ACTH administered one hour prior to the 14C-AA increased the uptake of AA by both glands. These results indicate that properly labeled AA may be an effective pituitary and adrenal scanning agent. Possible ways of labeling AA without changing its pharmacological properties are suggested.