The effects of platelet-activating factor and platelet-derived compounds on bovine luteal cell progesterone...

This study was conducted to characterize bovine platelets with respect to serotonin (5-HT) concentration and platelet-activating factor (PAF)-activation and to examine the in vitro effects of PAF and platelet-derived compounds on bovine luteal progesterone (P4) production. The concentration of 5-HT in platelets, as determined by high-performance liquid chromatography, was 538.8 +/- 40.83 ng/1 x 10(8) platelets. Based on a circulating platelet concentration range of 2.3 x 10(8) 5.8 x 10(8) platelets/ml, the circulating concentration of 5-HT would be approximately 1239-3125 ng/ml of blood. Bovine platelets were found to aggregate in response to PAF (1-40 ng/0.5 ml), with maximal aggregation occurring at 20-40 ng/0.5 ml. Coincubation of luteal cells with platelets (1 x 10(7)-4 x 10(8] enhanced luteal P4 production (p less than 0.05). Addition of the 5-HT receptor antagonist mianserin blocked the platelet-induced increases in P4 (p less than 0.05). Preincubation of platelets with indomethacin did not alter the production of P4 (p greater than 0.05), nor did the addition of propranolol (p greater than 0.05). Platelet-derived growth factor at 8 and 16 ng/ml enhanced basal P4 production (p less than 0.05) but had no effect on the responsiveness of luteal cells to luteinizing hormone (LH) (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)