Prostacyclin synthesis by endothelial cells from human umbilical veins: effect of cumulative population doublings.

There is a wide range of reported values for prostacyclin (PGI2) synthesis by cultured endothelial cells from human umbilical veins (HUVE). Part of this variation may be due to differences in isolation and culture conditions, but part may be due to previously unstudied variation in the number of population doublings (PDs) which the cells have undergone in vitro. Attention is now shifting to arachidonic acid (AA) metabolism by cells from adult human vessels and these cells may require increased PDs to obtain confluent cultures for testing. Therefore, we have examined the effect of number of cell population doublings as well as number of subcultivations on PGI2 synthesis using HUVE as a model system. Primary and first subcultivation cultures inoculated at high density, so that PDs at confluence were less than 4, synthesized 10 times as much PGI2 as the same isolates inoculated at low density with PDs greater than 4. Isolates inoculated and subcultivated so that the PDs at confluence after the fourth subcultivation were less than 6, showed 50% less PGI2 synthesis between the primary and first subcultivation and between the first and second subcultivations. Isolates with less than 4 PDs after the fourth subcultivation were carried further to determine the effect of extensive subcultivation. Four of six isolates showed a sudden increase in PGI2 synthesis which occurred between subcultivations 5 and 12 (PDs 4-6). These results demonstrate that AA metabolism is markedly affected by growth in culture and serial subcultivation.

Model system to study interaction of platelets with damaged arterial wall. II. Inhibition of smooth muscle cell proliferation by dipyridamole and AH-P719.

A new in vivo model for the initial events in atherogenesis was employed to investigate drugs which may inhibit intimal muscle cell proliferation following repeated limited endothelial cell injury. An artery forceps was placed over the central artery of the ear of an anesthetized rabbit for 30 min. The forceps were removed, blood flow resumed in the vessel, and platelets contacted the damaged vessel wall. When a vessel was injured two or more times the smooth muscle cells of the media migrated into the intima and proliferated there between 1 and 3 weeks after the last injury despite restoration of an apparently intact endothelium. The intima of control undamaged vessels sometimes contained a few individual smooth muscle cells while vessels injured two, four, or six times showed correspondingly increasing numbers of layers of intimal smooth muscle cells covering increasing amounts of the intima. Arteries from thrombocytopenic rabbits showed, at most, a single layer of smooth muscle cells covering a small area. In rabbits pretreated with dipyridamole (1.5 mg/kg) for 3 days before each injury, proliferation was also limited to a small area. Neither aspirin (8 mg/kg) nor ticlopidine (40 mg/kg, 5X over 3 days), which inhibit platelet aggregation ex vivo, nor the continuous presence of heparin (800 U/kg, bid), reported to inhibit smooth muscle cell growth in vitro and in vivo, prevented smooth muscle cell proliferation in response to two injuries. However, a potent inhibitor of platelet cyclic-adenosine monophosphate (cAMP) phosphodiesterase, AH-P719 (1.5 or 2.1 mg/kg), was able to inhibit intimal smooth muscle cell proliferation in doses that inhibited platelet aggregation ex vivo.

Alloxan-induced hyperglycemia in rabbits and the response of platelets to aggregating agents in vitro and to exposed subendothelium in vivo.

Many patients with diabetes mellitus show increased platelet aggregation and prostaglandin synthesis in response to physiological agents such as ADP and collagen when their platelets are tested in platelet-rich plasma or washed platelet suspensions. However, the relationship between increased platelet aggregation in vitro and increased thrombosis in vivo is difficult to establish with certainty. We have developed an in vivo model system in rabbits which tests the response of platelets in circulating native blood to an arterial vessel wall with limited damage such as might occur in arteries of patients with diabetes mellitus. We have used this model system to investigate whether 5 to 9 weeks of alloxan-induced hyperglycemia increases platelet adhesion and aggregation on a damaged vessel wall in vivo as well as platelet aggregation in vitro. Our results show that rabbit platelet function is not affected by extreme hyperglycemia and suggest that alloxan-induced diabetes in the rabbit may not be a good model for human diabetes mellitus.

Model system to study interaction of platelets with damaged arterial wall. I. Inhibition of platelet adhesion to subendothelium by aspirin and dipyridamole.

An experimental model system has been developed to study the interaction of platelets with a damaged vessel wall, in vivo, without deep surgical intervention. Endothelium of the central ear artery of an anesthetized rabbit is damaged by placing artery forceps on the ear directly over the vessel. Forceps are removed 30 min later and blood flow resumes. After 30 min, blood is washed out with Tyrode's solution and the vessel is perfused with 1% glutaraldehyde solution. Tissue containing the vessel is then removed and further prepared for scanning and transmission electron microscopy. Damage to the endothelium observed by scanning electron microscopy included separation of adjacent endothelial cells (EC); partial destruction and lifting up of some EC, exposing subendothelium; and denudation of larger areas of endothelium. Disc-shaped platelets were seen clinging to some damaged endothelial cells. Platelets adhered, formed pseudopods, and spread over the surface of some areas of exposed subendothelium. The extent of platelet adhesion to exposed subendothelium was estimated by eight "blind" evaluators and the average taken. Aspirin (8 mg/kg, ip) significantly inhibited adhesion (P less than 0.05) when compared to controls. No other agent tested gave significant inhibition after a single treatment. Dipyridamole (1.5 mg/kg, ip) given five times on 3 successive days, inhibited adhesion significantly (P less than 0.001). Heparin (800 U/kg, iv) or dipyridamole (0.7 mg/kg, ip) enhanced the inhibitory effect of aspirin (8 mg/kg, ip), with either combined treatment giving P less than 0.001.

A quick method for screening platelet dysfunctions using the whole blood lumi-aggregometer.

Patients who present with a clinical history suggesting a bleeding disorder are often tested initially for a clotting defect rather than for platelet dysfunction, due to the length of time necessary to complete a platelet function study in platelet-rich plasma. We have developed a sensitive method for measuring platelet aggregation and release of ATP employing the Whole Blood Lumi -Aggregometer. This method makes it possible to quickly detect patients who require further study for possible platelet function disorders such as cyclooxygenase deficiency, storage-pool defect, thrombasthenia, and von Willebrand's disease. The results obtained with this electrical impedance instrument do not differ from those obtained with the conventional optical method. However, it is now possible to recognize a platelet function defect within 30 min of obtaining a 5 ml sample of citrated whole blood. Further, platelets of unusual size or density are not lost to testing through centrifugation.

Early morphological changes in the endothelium of a peripheral artery of rabbits fed an atherogenic diet.

The effect of an atherogenic diet on the endothelium of the central artery of the rabbit ear was studied by scanning and transmission electron microscopy. Examination of the inner surface of the artery after only 5 weeks on the diet revealed morphological changes including irregularly shaped cells, breaks at intercellular junctions, swelling of the membrane over the central part of the cells, and occasional holes in the cells. By 9 weeks more severe damage was seen including lifting off of cells and some holes. In addition, arrays of dark spots were seen by scanning electron microscopy in some cells in arteries of rabbits fed the diet for 5 to 9 weeks. The dark spots may correspond to abnormally large vacuoles seen inside endothelial cells by transmission electron microscopy. The central ear artery and aorta of some rabbits were tested for their ability to convert arachidonic acid into prostacyclin and thromboxane A2 by radioimmunoassay of the stable metabolites 6-keto-prostaglandin F1 alpha and thromboxane B2. The vessels from rabbits fed the atherogenic diet did not differ from vessels of rabbits on the control diet in their production of either metabolite.

Backscattered electron imaging to visualize arterial endothelial detachment in the scanning electron microscope.

The endothelium of the central ear artery of an anesthetized rabbit was damaged by placing artery forceps on the ear over the vessel for 30 min. After removal of the forceps, blood was allowed to flow through the injured vessel for 30 min. Blood flow was then stopped, blood was washed out of the artery in situ and initial fixation with 1% glutaraldehyde was begun. Specimens of the vessel containing the damaged region were postfixed in 3% cacodylate buffered glutaraldehyde and prepared for SEM examination after methenamine silver staining or following post fixation with osmium. Backscattered electron imaging (BEI) of silver stained specimens with inverted signal polarity showed "black" endothelial nuclei similar to darkly stained nuclei of conventional light microscope slide preparations. Secondary electron imaging (SEI) of corresponding sites stained with silver also showed endothelial nuclei. An interruption of the normal pattern of nuclei indicated a detached area of endothelium where subendothelium was exposed. Platelets were observed adhering to the surface of the exposed subendothelium. Injury to the endothelium was seen more readily in silver stained preparations as voids in the nuclear pattern as compared with conventional SEI preparations, postfixed with osmium, which did not show well defined nuclei.