Indium-111-labeled human platelets: uptake and loss of label and in vitro function of labeled platelets.

Abstract

Indium-111 (/sup 111/In)-oxine has recently been suggested as a new agent for isotopic labeling of platelets. In this paper, the results of in vitro studies on /sup 111/In-oxine uptake by and loss from human platelets as well as function of labeled platelets are presented. /sup 111/In-oxine was rapidly taken up by platelets in a plasma-poor medium, with a mean labeling efficiency of 77% at 37/sup 0/C. Uptake of label was reduced at lower temperatures but did not appear to be dependent on intact platelet energy metabolism. The percentage uptake of /sup 111/In-oxine was found to be similar at concentrations between 1 and 30 ..mu..Ci/ml platelet suspension but was markedly reduced in the presence of small concentrations of plasma proteins. The in vitro sensitivity of /sup 111/In-labeled platelets in response to different aggregating and release-inducing stimuli was similar to that of unlabeled control platelets. Uptake of /sup 111/In-oxine by thrombin-degranulated platelets was similar to that observed with intact platelets, and less than 4% of label was lost from /sup 111/In-labeled platelets upon exposure to strong release-inducing agents. This indicates that the label is bound to nonreleasable platelet components. Less than 3% of label was lost from /sup 111/In-labeled platelets during amore » 2 hr in vitro incubation at 37/sup 0/C. These in vitro findings are consistent with and support previously reported in vivo evidence indicating that /sup 111/In-oxine may be a suitable and promising new isotopic label for studies of platelet survival, organ distribution, and thrombus localization.« less