Further studies on the control of arachidonic acid turnover in guinea-pig endometrium in relation to prostaglandin production.

The amounts of phospholipids in the guinea-pig endometrium were phosphatidylcholine (PC) greater than phosphatidylethanolamine (PE) = sphingomyelin (Sph.) greater than phosphatidylserine (PS) + phosphatidylinositol (PI). There were no significant differences in the amounts of any of these phospholipids in endometrium between Days 7 and 15 of the cycle. The de novo synthesis of PC was 5- to 10-fold higher than the synthesis of PC from PE in guinea-pig endometrium. There were no differences in the amounts of PC formed by either pathway, and in the amounts of PI synthesized by guinea-pig endometrium between Days 7 and 15 of the cycle during a 6 h culture period. The increased incorporation of arachidonic acid into phospholipids of guinea-pig endometrium on Day 15 compared to Day 7 cannot be accounted for by an increase in phospholipid content or increased phospholipid synthesis on the former day. Following a 24 h labelling period of endometrial lipids with [3H] arachidonic acid (3H-AA), there was a significant decrease in the amount of 3H-AA in PC and PE on Day 15, but not on Day 7, following a further 48 h culture period. Progesterone, oestradiol and A23187 did not affect the amounts of 3H-AA released from the various lipid classes in guinea-pig endometrium during the time periods of culture studied. It is concluded that PC and PE may be the source of arachidonic acid for increased PGF2 alpha synthesis by guinea-pig endometrium after Day 11 of the oestrous cycle. The lack of changes in PI content and PI synthesis between Days 7 and 15 of the cycle indicates that stimulation of the PI cycle is not involved in the biochemical processes which lead to increased AA release and PGF2 alpha synthesis in guinea-pig endometrium after Day 11 of the cycle.