Abstract, Morphological studies of developing capillaries and observations of alterations in capillaries associated with pathologic neovascularization indicate that pericytes may act as suppressors of endothelial cell (EC) growth. We have developed systems that enable us to investigate this possibility in vitro. Two models were used: a co-culture system that allowed direct contact between pericytes and ECs and a coculture system that prevented physical contact but allowed diffusion of soluble factors. For these studies, co-cultures were established between bovine capillary ECs and the following growth-arrested cells (hereafter referred to as modulating cells): pericytes, smooth muscle cells (SMCs), fibroblasts, epithelial cells, and 3T3 cells. The modulating cell type was growth arrested by treatment with mitomycin C before coculture with ECs. In experiments where cells were cocultured directly, the effect of co-culture on EC growth was determined by comparing the mean number of cells in the co-cultures to the mean for each cell type (EC and modulating cell) cultured separately. Since pericytes and other modulating cells were growth arrested, any cell number change in co-cultures was due to EC growth. In the co-cultures, pericytes inhibited all EC proliferation throughout the 14-d time course; similar levels of EC inhibition were observed in SMC-EC co-cultures. Co-culture of ECs with fibroblasts, epithelial cells, and 3T3 cells significantly stimulated EC growth over the same time course (30-192% as compared to EC cultured alone). To determine if cell contact was required for inhibition, cells were co-cultured using Millicell chambers (Millipore Corp., Bedford, MA), which separated the cell types by 1-2 mm but allowed the exchange of diffusible materials. There was no inhibition of EC proliferation by pericytes or SMCs in this co-culture system. The influence of the cell ratios on observed inhibition w~ts assessed by co-culturing the cells at EC/perieyte ratios of 1:1, 2:1, 5:1, 10:1, and 20:1. Comparable levels of EC inhibition were observed at ratios from 1:1 to 10:1. When the cells were co-cultured at a ratio of 20 ECs to 1 pericyte, inhibition of EC growth at 3 d was similar to that observed at other ratios. However, at higher ratios, the inhibition diminished so that by the end of the time course the co-cultured ECs were growing at the same rate as the controls. These results suggest that pericytes and SMCs can modulate EC growth by a mechanism that requires contact or proximity. We postulate that similar interactions may operate to modulate vascular growth in vivo.M ATURE capillaries and postcapillary venules are comprised of two cell types-endothelial cells (ECs) 1 and pericytes. Pericytes exist in intimate association with ECs, forming a single layer that covers varying amounts of the abluminal EC surface. This arrangement, unique to small vessels, is characterized by frequent sites of contact between the ECs and pericytes. The interaction between ECs and pericytes has been extensively analyzed at both t...

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We studied histamine metabolism, i.e., histldine decarboxylase (HD)-mediated synthesis and hlstamlnase-mediated catabollsm, in relation to intracellular histamine content in both aortic endothelial and subjacent smooth muscle cells of control and diabetic rats. Diabetes was Induced by a single jugular vein Injection of streptozotocln (55 mg/kg in acidified saline, pH 4.5), and animals were held for either 2 or 4 weeks following overt manifestation of diabetes. An additional 4-week diabetic group received Insulin (lletln NPH, 10 U per 24 hour) during the last week. With respect to control values, the histamine content of aortic endothelial cells increased 138%, HD activity Increased 250%, and histaminase activity decreased 50% over the 4-week period. In subjacent smooth muscle cells, the histamine content Increased In excess of 150%, HD activity Increased more than 300%, and histaminase activity decreased in excess of 30%. Insulin treatment for the last week resulted In complete reversal of all these changes. These results support the concept that a large vessel response similar to the microclrculatory prolonged phase of inflammation occurs In experimental diabetes, a change similar to that occurring in experimental atherosclerosis. They also Indicate that both synthetic and catabollc changes occur In histamine metabolism under these conditions, changes that alter arterlai wall histamine pools, and suggest that Insulin administration under conditions of experlmentai diabetes may modulate aortic histamine metabolism and the resultant Intraaortlc histamine pools.

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