The effect of a thymic epithelial culture supernate on rabbit platelet aggregation and intracellular cyclic nucleotide levels

Abstract

Supernates of thymic epithelial cell culture (STEC) strongly inhibit the aggregation induced by the addition of adenosine diphosphate (1 μM) or thrombin (0.5 unit per ml) to washed platelet suspensions. At the same time, STEC increased the levels of adenosine 3', 5'-cyclic monophosphate (cyclic AMP) and guanosine 3', 5'-cyclic monophosphate (cyclic GMP) in platelets in a dose-dependent manner. In contrast the supernates from Chang, Hela or HCC-M cells did not affect platelet aggregation induced by ADP and intracellular cyclic nucleotide levels. Within 2 min after the treatment with STEC, more than 50% of the maximum inhibitory activity on platelet aggregation and increases in intracellular cyclic AMP were observed. These activities were not altered when STEC was boiled for 5 min, but disappeared following STEC treatment with pronase E. These activities were found predominantly in the fraction>1, 000 daltons. The level of prostaglandin E derivertives in STEC was about two times that found in the control culture medium. In these data suggest that the biological activity of STEC in the platelets might be attributed to thymosin-like polypeptides and prostaglandins.