Adenine uptake by rat peritoneal macrophages in vitro.

Abstract

Adenine uptake by rat peritoneal macrophages (PM) in vitro was studied by the autoradiographic technique using [14C]adenine ([14C]A), [3H]adenine ([3H]A) and, as control, [3H]thymidine ([3H]TdR).It was found that the incorporation of either [14C]A or [3H]A by the major population of PM took place to a great extent in contrast to no uptake by peritoneal leucocytes other than PM. In the case of [14C]A labeling, the percentages of labeled PM were 96±3.3 and the mean grain counts per cell were 25±7.6. In the case of [3H]A, the corresponding figures were 83±7.5 and 16±4.1, respectively. Since the label of the major population of PM disappeared almost completely following treatment with RNase, it is apparent that adenine was incorporated into the RNA of these cells. In addition to RNA labeling, an extraordinarily strong labeling of DNA with either [3H]TdR, [14C]A or [3H]A was observed in a limited number of blast-like cells (less than 1% of PM). Between such blast-like cells and the major population of PM, however, there occurred no transitional forms. This indicates that the blast-like cells do not serve as the stem cells for PM under the conditions of this study.In view of our previous observations that the incorporation of [14C]A into DNA and RNA, the former in particular, takes place to an especially great extent in the monocyte precursors in the bone marrow, also in a portion of the blood monocytes of rats (9, 11, 12), a strong adenine requirement of PM, that was observed in the present study, though limited to that for RNA synthesis, supports the view that PM are derived from monocytes produced in the bone marrow.