New insights in endothelial and smooth muscle cell communication.

Based on immunohistochemical techniques against connexins and the intercellular flux of staining molecules, it has previously been shown that electrotonic communication occurs among endothelial and vascular smooth muscle cells, this due to the presence of myoendothelial gap junctions. The aim of this study was to evaluate the density of myoendothelial contacts in the left coronary and internal mammary arteries as well as in the left saphenous vein by means of electron microscopy, the distance between both cells participating in an myoendothelial contact with a semi-automatic image analysis system and the presence of homocellular and heterocellular gap junctions between endothelial and smooth muscle cells by using the immunohistochemical technique and confocal microscopy in thoracic aorta were also analyzed. The results are that all blood vessels studied present myoendothelial contacts, while density studies show that they are more abundant in the saphenous vein. The myoendothelial contact distance is constant and in no case the cytoplasmic processes reach the plasma membrane of the partner cell toward which they are advanced. Homocellular gap junctions were found between smooth muscle cells and between endothelial cells. Heterocellular gap junctions were absent, evidencing the possibility that signaling molecules between endothelial and smooth muscle cells may be transferred through plasma membranes as was once thought and not necessarily by electrotonic communication.

Spermine increases arginase activity in the liver after carbon tetrachloride-induced hepatic injury in Long-Evans rats.

Arginase is the enzyme which synthesizes urea and ornithine, a precursor from which putrescine, spermidine and spermine are formed. These natural polyamines have been implicated in cell growth, replication and wound healing. The present study evaluated the possibility that spermine increases arginase activity and reduces liver damage caused by carbon tetrachloride. Intraperitoneally injected spermine at a dose of 1 mg/kg after a single intragastric administration of carbon tetrachloride (1.6 ml/kg) increased arginase activity (6.30-7.79 microg urea/mg protein per min) (P<0.05) as well as total protein content (0.29-0.37 mg/mg dry weight) in hepatic tissue, compared to the group which only received carbon tetrachloride. When liver cell damage was biochemically assessed, the carbon tetrachloride-treated group showed a 20-fold increase in serum glutamic oxaloacetate transaminase, compared to the control group (P<0.05), and this was significantly diminished by the administration of spermine (P<0.05). Serum triglycerides increased four times compared to the control group as a result of the carbon tetrachloride treatment and were diminished by spermine as well. These results indicate that spermine may play a role in the recovery of liver tissue after carbon tetrachloride-induced liver injury, maybe by increasing the synthesis of putrescine, a polyamine which has been found out to participate in the recovery of the hepatic tissue after an insult with carbon tetrachloride.