Potentiating effects of hyper-osmolality and epidermal growth factor on the release of arachidonic acid in human glomerular mesangial cells

Studies were performed to determine the interactive effects of high concent rations of glucose (HG) and epidermal growth factor (EGF) on the release of arachidonic acid (H-3-AA) in human glomerular mesangial cells (MC) in cult ure. Since high glucose has been reported to increase the mass of diacylgly cerol (DAG) in MC, the HG-induced release of H-3-AA was compared to that in itiated by the phorbol ester, PMA. It was found that when media contained h igh levels (25 mM) of glucose, the release of H-3-AA was increased signific antly by 8.4% (change from control) after 1 h of exposure and was maintaine d at values not significantly different from this level for the next 2 h. A fter 3-h exposure, there was no significant difference between 25 and 50 mM glucose, suggesting that the effects of glucose are saturating at 25 mM. A fter 1-h exposure, H-3-AA release was also increased by PMA; however, the i ncrease was larger and the peak increase was delayed until after 1 h. H-3-A A release was significantly increased by epidermal growth factor (EGF) by 8 .5% after 1 h and was maintained at this level after 2 and 3 h of exposure. In the presence of HG, EGF increased H-3-AA release by 24.6% after the Ist hour and by 20.4 and 19.4% after the 2nd and 3rd hours, respectively. Mann itol (20 mM), added as an osmotic control, increased H-3-AA release by 6.2% and also significantly enhanced the effects of EGF after 3 h. The experime ntal values (19.0%) for the release of H-3-AA after 3-h exposure to EGF in combination with either high glucose or mannitol were significantly greater than the expected (added) values (12.1%). These results demonstrate that a s a result of an elevated solution osmolality, high glucose acts synergisti cally with EGF to increase the release of H-3-AA in human mesangial cells. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.