Endothelin releasing activity in calf serum and porcine follicular fluid

Bovine calf serum (CS) and porcine follicular fluid (PFF) added to bovine aortic endothelial cells (BAEC) in culture stimulate endothelin (ET) release. Sorbent extraction of acidified calf serum and PFF using Bond Elut C 18 yields a product with an activity 30% that of the starting material. Fractionation of Bond Elut C 18 extracted CS or PFF using HPLC yields peaks of activity with retention times similar to those of TGF β and activin A, respectively. TGF β is 10-fold more potent than activin A to stimulate ET release from BAECs. The observation that TGF β and activin A are dose-additive but not effect-additive to stimulate ET release is compatible with the conclusion that these two substances act through a similar mechanism. Thus, TGF β and/or activin A-related peptides may contribute to the ET releasing activity observed in acidified Bond Elut C 18 extracted CS and PFF. The identity of ET-releasing activity in native CS and PFF remains to be established.