ETA-RECEPTOR AND ETB-RECEPTOR ANTAGONISTS SYNERGISTICALLY INCREASE EXTRACELLULAR ENDOTHELIN-1 LEVELS IN PRIMARY RAT ASTROCYTE CULTURES

Astrocytes produce and bind endothelins (ETs), suggesting that these c ells have ET autoregulatory and eliminatory functions. To further inve stigate these functions in primary rat astrocytes, ET-1 levels in the cell culture media (RIA/HPLC) and intracellular content of ET-1 mRNA ( RT PCR) were measured under basal and stimulated (thrombin, 2.2 U/ml) conditions in the presence and absence of ETA and ETB selective antago nists (BQ123 or LU135252, and BQ788, respectively). Neither basal nor stimulated ET-1 levels in astrocyte media were influenced by ETA or ET B antagonists alone, but were significantly increased by a combination of both. ir ET-3 levels were not affected by antagonist treatment. Ex ogenous ET-1, added to the cultures, was rapidly cleared from the supe rnatant; this clearance was markedly inhibited by a combination of BQ1 23 and BQ788. ET-1 mRNA levels were not altered by any treatment. To c onclude, in primary rat astrocyte cultures, extracellular ET-1 is clea red by binding to ET-receptors, apparently involving both, ETA and ETB sites. Thus, a blockade of the astrocytic ET eliminatory function as a consequence of the in vivo application of non-selective ET receptor antagonists may lend to increased extracellular ET levels in the brain . (C) 1998 Elsevier Science B.V.