This study was undertaken to examine the cell cycle characteristics of bovine fetal and adult somatic cells (fetal fibroblasts, adult skin and muscle cells, and cumulus cells) after culture under a variety of conditions ; 1 ) growth to 60- 70% confluency (cycling) , 2) serum starvation, 3) culture to confluency. Cell -cycle phases were determined by flow cytometry with propidium iodide staining enabling the calculation of percentages of cells in GO /G1, S and G2 /M. The majority was in GO /GI regardless of cell type and treatment. Serumstarved or confluent cultures contained higher percentages of cells in GO /G1 (89.5-95.4% ; P <0.05) . Percentages of cells in GO /G1 increased as cell size decreased regardless of the cell type and treatment. In the serum-starved and confluent cultures, about 98% of small cells were in GO /G1. Serum-starved cultures contained higher percentages of small cells (38.5-66.9%) than cycling and confluent cultures regardless of cell type (P < 0.05) . After trypsinization of fetal fibroblasts and adult skin cells that were serum-starved and cultured to confluency, the percentages of cells in GO /G1 increased (P < 0.05) on incubation for 1.5 (95.7-99.5%) or 3 hr (95.9-98.6%). These results verify that serum starvation and culture to confluency are efficient means of synchronizing bovine somatic cells in GO /G1, and indicate that a more efficient synchronization of the cells in GO /G1 can be established by incubation for a limited time period after trypsinization of serum-starved or confluent cells.

Endothelial cells are important for maintenance of vascular integrity by producing a variety of bioactive molecules such as nitric oxide (NO) . Recent evidence has suggested that there are some differences in characteristics between endothelial cells from different origins. Here we examined responses of two typical endothelial cells to hepatocyte growth factor (HGF), which induces endothelium-dependent relaxation of microvessels. Stimulation of human umbilical vein endothelial cells (HUVEC) and bovine aortic endothelial cells (BAEC) with HGF increased endothelial NO synthase activity, accompanied with an increase of activity-related site-specific phosphorylation of protein kinase B/Akt. However, HGF stimulated phosphorylation of p38 mitogenactivated protein kinase (MAPK) only in HUVEC, but not in BAEC, while it induced phosphorylation of p44 /p42 MAPK in both cells. These results suggest that HGF transduces different intracellular signals between aortic and umbilical venous endothelial cells, and that the differences might represent divergent endothelial responses to growth factors, especially those that activate receptor-tyrosine kinases.