Changes in phospholipase A2 in myometrium of the guinea pig uterus during pregnancy.
Phospholipase A2 activity has been measured in membrane and cytosolic fractions from non-pregnant and pregnant guinea pig myometrium has been studied. Enzyme activity was measured with 1-stearoyl-2- [3H]arachidonoyl-phosphatidylcholine exhibiting Michaelis-Menton kinetics with Km of 83.8 +/- 21.6 and 53.2 +/- 14.1 for membrane and cytosolic enzymes respectively. Fractionation of the myometrium from non-pregnant guinea pigs suggested that 35% of the activity was membrane associated compared with 20% (P < 0.01) in tissue from pregnant animals. In the presence of 1 mM calcium total activity rose from 3.03 +/- 0.41 to 1737 +/- 368 nmol/h per uterus between non-pregnant and late pregnancy. Calcium activated the membrane enzyme, but the effect was greater late in pregnancy with almost a 6-fold increase in activity at 1 mM calcium compared with a doubling in membrane from non-pregnant guinea pigs. The K0.5 for calcium activation was about 150 microM. Immunoblotting with anti-human-110 KDa phospholipase A2 showed in guinea pig uterus a 34 KDa form of the enzyme that, consistent with changes in activity, showed a fifteen-fold increase in quantity between non-pregnant and late pregnancy. The data are consistent with dramatic increases in the capacity for arachidonic acid release and prostaglandin production in the guinea pig myometrium late in pregnancy.
Khouja
A
A
Laboratory of Cellular and Developmental Physiology, University of Oxford, John Radcliffe Hospital, UK.
Jones
C T
CT
D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D002462:Cell Membrane / Q000201:enzymology; D004789:Enzyme Activation; D005260:Female; D006168:Guinea Pigs; D007700:Kinetics; D009215:Myometrium / Q000201:enzymology*; D010713:Phosphatidylcholines / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000378:metabolism*
D010713:Phosphatidylcholines; C043644:1-stearoyl-2-arachidonylphosphatidylcholine; D016718:Arachidonic Acid; D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium