Changes of DNA-acridine orange binding in monocytes and endothelial cells of hypertensive arteries.

The interactions of monocytes and endothelial cells were examined employing acridine orange (AO) binding to chromatin as an electron microscopic probe for studying changes in nuclear activity. The number of AO labeled nuclei were determined in adherent and sub-endothelial monocytes, and endothelial cells either associated with or devoid of monocytes in mesenteric arteries of renal hypertensive and normotensive rats. No AO-positive cell nuceli were found in the few adherent monocytes in the normotensive rats while in hypertensive rats 63% of the adherent monocytes and 86% of the subendothelial monocytes were labeled by AO. The number of AO-positive cell nuclei increased in the endothelium from 2% in normotensive rats to 17% in hypertensive animals. Fifty-seven percent of these endothelial cells were associated with monocytes adhering to their surfaces. Thirty-nine (52%) of AO-positive and 24 (52%) of AO-negative cell pairs represented 84% of cell pairs with identical nuclear activity. These findings indicate a sequential interaction of monocytes and adjacent endothelial cells recognized at the nuclear level. According to other experimental work the binding capacity of chromatin for AO increases as cell nuclei are reactivated by stimulation of cell proliferation. In addition, AO labeling of chromatin visualized electron microscopically is confined to three of the four stages of the cell cycle. Therefore AO labeling in the present experiments might indicate the reentrance of monocytes and endothelial cells into the cell cycle.