EFFECT OF EPINEPHRINE ON A SPECIFIC ORGANELLE OF ENDOTHELIAL CELLS OF BLOOD VESSELS

Endothelial cells of vertebrate blood vessels contain specific cytoplasmic organelles, distinguishable from other dense bodies by their rod shape and internal tubular substructure. The following observations led to the hypothesis that these organelles could correspond to a procoagulative substance previously observed in arterial walls. a) These organelles have some resemblance to α-granules of thrombocytes which proved to be procoagulative elements. b) Intima and endothelium of human aorta contain thromboplastic substances. c) Large blood vessels contain more organelles, a fact which could be explained as an indication of their blood-directed function. d) The epinephrine perfused rabbit aorta delivers a coagulation activating substance into the perfusate. To check this hypothesis strips of aortic wall of five rats were incubated in 0.5 μg-% epinephrine solution for 20 sec and as controls in Ringer solution. By comparison some material was directly fixed by immersion in 1% OsO4. The volume-density of organelles in endothelial cytoplasm was determined by means of stereologic methods. On the average the volume-density decreased from 0.93% in immediatly fixed, to 0.83% in Ringer incubated, and to 0.53% in epinephrine incubated tissue samples. The diminution after Ringer incubation can be explained by swelling of cytoplasm. The loss of some 40% of organelles between Ringer and epinephrine incubated material is statistically highly significant. Evidence is presented that the organelles are expulsed towards the vessel lumen. These results give support to the hypothesis that these organelles could contain a procoagulative substance of aortic endothelium postulated by several authors. Further experiments are needed to prove this relationship. © 1968 Springer-Verlag.