GROWTH OF BOVINE RETINAL PERICYTES AND ENDOTHELIAL-CELLS IN HIGH HEXOSE CONCENTRATIONS

Selective loss of capillary pericytes occurs early in diabetic and gal actosaemic retinopathies, at a stage when endothelial cells are still spared. To ascertain whether such loss is directly related to high hex ose concentrations, the replication of bovine retinal pericytes and en dothelial cells was studied by culturing them in media containing 5.6. mmol/1 glucose alone and enriched with extra glucose, mannitol or gala ctose to achieve final concentrations of 16.7, 27.8 and 50.0 mmol/l. A t the end of the incubation there were significantly less pericytes/cu lture well in 16.7 mmol/l glucose (341 +/- 78 x 10(3), mean +/- SEM, p = 0.027) and galactose (304 +/- 55 x 10(3), p = 0.046) than in 5.6 mm ol/l glucose (417 a 98 and 355 +/- 75 x 10(3) for separate experiments , respectively). Mannitol had no such effect (343 +/- 52 vs. 337 +/- 5 2 x 10(3)). Endothelial cells did not change in number, except in 50.0 mmol/l glucose (533 +/- 66 vs. 629 a 67 x 10(3) at 5.6 mmol/l; p = 0. 026) and 50.0 mmol/l galactose (440 +/- 48 vs. 592 +/- 51 x 10(3); p = 0.013). To verify if these effects are due to decreased replication, the uptake of H-3-thymidine was measured in pericytes and endothelial cells subjected to the same concentrations of glucose, mannitol and ga lactose. In pericytes, thymidine uptake was reduced in the presence of 16.7 mmol/l glucose (p = 0.003, compared to 5.6 mmol/l) and galactose (p = 0.027) but not mannitol. Pericyte counts and thymidine uptake we re reduced for concentrations of glucose, galactose and mannitol highe r than 16.7 mmol/l. In contrast, non consistent inhibition of replicat ion was produced on endothelial cells. Finally, confluent pericytes we re pretreated with mitomycin-C, a non lethal inhibitor of DNA synthesi s, and left in glucose and galactose 16.7 mmol/l. They did not decreas e in number when compared to the 5.6 mmol/l controls, suggesting that neither sugar causes excess cell death. In conclusion, retinal pericyt es appear more vulnerable than endothelial cells to high hexose concen trations. This effect is not entirely due to excess extracellular osmo tic pressure. It may account for early loss of mural cells in diabetic and galactosaemic retinopathies.