title: Phospholipase A2 activity in endometrium from early pregnant and non-pregnant ewes.
abstract: In the ewe, synthesis of the luteolytic factor, prostaglandin F2 alpha, increases from day 13 to the end of the estrous cycle. Availability of free arachidonic acid is usually the rate-limiting step in prostaglandin biosynthesis. Phospholipase A2 (PLA2) may be the key enzyme for the hydrolysis of arachidonic acid from membrane-bound phospholipids. To investigate uterine PLA2 activity during the estrous cycle and early pregnancy, we monitored the release of [14C]oleic acid from the substrate 1-palmitoyl-2-[14C]oleoyl-phosphorylcholine by homogenates and cytosolic fractions of endometrium from ewes on days 12, 14 and 16 of the estrous cycle or pregnancy. We observed that PLA2 activity dropped by 58% (p < 0.02) in day-16 pregnant endometrium compared to day-16 non-pregnant endometrium. We then investigated whether the reduced PLA2 activity was due to induction of a specific inhibitor. The PLA2-inhibitor activity was determined by monitoring the inhibition of release of [14C]oleic acid from the radioactive substrate by porcine pancreatic PLA2. Inhibition by endometrial homogenates of pregnant animals of the control enzyme activity was 27% and only 14% by cyclic ones. Inhibition was dose-dependent and was as high as 53% (p < 0.01) with 1 mg protein from pregnant endometrial homogenates. Endometrial PLA2 behaved as a Michaëlian enzyme in the endometrium of day-16 cyclic ewes (Km = 79.4 mumol/l). Furthermore, the inhibitory activity from pregnant endometrium had characteristics of competitive inhibition. Our results suggest that inhibition of endometrial PLA2 activity could occur in early pregnant ewes.
authors.affiliation: Unite d'Endocrinologie de I'Embryon, Station de Physiologie Animale, I.N.R.A., Jouy-en-Josas, France.
authors.forename: J P
authors.initials: JP
authors.lastname: Tamby
authors.forename: G
authors.initials: G
authors.lastname: Charpigny
authors.forename: P
authors.initials: P
authors.lastname: Reinaud
authors.forename: J
authors.initials: J
authors.lastname: Martal
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D015237:Dinoprost / Q000096:biosynthesis; D004717:Endometrium / Q000201:enzymology*; D004971:Estrus / Q000502:physiology; D005260:Female; D007700:Kinetics; D019301:Oleic Acid; D009829:Oleic Acids / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054467:Phospholipases A2; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*
chemical_list: D009829:Oleic Acids; D010713:Phosphatidylcholines; D016718:Arachidonic Acid; D019301:Oleic Acid; D015237:Dinoprost; D010741:Phospholipases A; D054467:Phospholipases A2; C028694:1-palmitoyl-2-oleoylphosphatidylcholine