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 bee n studied. Enzyme activity was measured with 1-stearoyl-2-[H-3]arachid onoyl-phosphatidylcholine exhibiting Michaelis-Menton kinetics with K( m) of 83.8 +/- 21.6 and 53.2 +/- 14.1 for membrane and cytosolic enzym es respectively. Fractionation of the myometrium from non-pregnant gui nea pigs suggested that 35% of the activity was membrane associated co mpared with 20% (P<0.01) in tissue from pregnant animals. In the prese nce 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. Calciu m activated the membrane enzyme, but the effect was greater late in pr egnancy with almost a 6-fold increase in activity at 1 mM calcium comp ared with a doubling in membrane from non-pregnant guinea pigs. The K0 .5 for calcium activation was about 150 muM. Immunoblotting with anti- human-110 KDa phospholipase A2 showed in guinea pig uterus a 34 KDa fo rm of the enzyme that, consistent with changes in activity, showed a f ifteen-fold increase in quantity between non-pregnant and late pregnan cy. The data are consistent with dramatic increases in the capacity fo r arachidonic acid release and prostaglandin production in the guinea pig myometrium late in pregnancy.