INFLUENCE OF CELL CYCLING ON MAGNITUDE OF RESPONSE OF HUMAN UMBILICAL VEIN ENDOTHELIAL CELLS (EC) TO NOREPINEPHRINE (NE) AND HISTAMINE (H)

EC have several roles in preventing thrombosis. Efficiency with which EC fulfill these might well influence outcome of potentially thrombotic stimuli. Thus, factors that influence EC function are of interest. As a general measure of EC response to NE and H the level of cAMP was measured. EC were harvested and passaged by enzymatic digestion and grown in DMEM plus 10% fetal calf serum and antibiotics. cAMP was assayed by radioimmunoassay. Percentage cycling cells was determined by autoradiography of cultures pulse labeled with tritiated thymidine and was increased by hydroxyurea treatment.

Basal cAMP was remarkably consistent (less than 10% difference) for cells isolated from different cords, studied after different number of passages, fresh or frozen and with varying percentage of cells cycling. However, magnitude of response to agonists was highly variable. Within the same cell lot between 5-8 passages, magnitude of response was directly proportional to percentage of cycling cells but magnitude ofresponse for different cell lots varied over several fold.

EC response to NE was mediated through B-adrenergic receptors and that to H through H receptors. Variability might be caused by differences in receptor number or some intracellular process.