ALTERED ENDOTHELIN-L INDUCED CONTRACTION AND 2ND MESSENGER GENERATIONIN BOVINE RETINAL MICROVASCULAR PERICYTES CULTURED IN HIGH GLUCOSE MEDIUM

The effect of simulated hyperglycaemia on bovine retinal pericytes was studied following culture of these cells for 10 days under normal (5 mmol/l) and elevated (25 mmol/l) glucose conditions in the absence of endothelial cells. Pericytes cultured under high ambient glucose exhib ited both a delayed and reduced contractile response following stimula tion with endothelin-1. Stimulation with 10(-7) mol/l endothelin-1 for 30 s caused significant contraction in cells grown in both 5 mmol/l a nd 25 mmol/l glucose. The former also contracted significantly with 10 (-8) mol/l endothelin-1. Further, at all concentrations tested, statis tical comparison of the time course of contraction showed a significan t difference (p < 0.02) in the reduction of planimetric surface area b etween the two cell groups. Since neither binding of endothelin-1 nor the number of receptors for this peptide were significantly different (p > 0.1) between bovine retinal pericytes grown for 10 days under nor mo- or hyperglycaemic conditions, it became apparent that the altered contractility in bovine retinal pericytes following culture in high gl ucose must be due to post-binding intracellular disturbance(s). Indeed , both basal and 15 s post-stimulation with 10(-8) mol/l endothelin-1, levels of inositol trisphosphate were significantly reduced (p < 0.05 and p < 0.02, respectively) in pericytes cultured for 10 days in 25 m mol/l glucose. These results show that endothelial-independent alterat ions in contractility of pericytes occur when they are grown in condit ions which simulate hyperglycaemia. The results also suggest that the observed attenuation in response to endothelin-1 stimulation evident i n pericytes grown under simulated hyperglycaemic conditions is not due to alterations in peptide binding.