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Ovine myometrial cytosol inhibits phospholipase A activity, in vitro
G E Rice1, M H Wong, G D Thorburn
1Department of Physiology, Monash University, Clayton, Victoria, Australia.
Abstract:
Myometrium obtained from pregnant ewes (30-80 days gestation) contains a factor which inhibits phospholipase A2 (PLA2) activity. The activity of this moiety was assessed using an in vitro porcine pancreatic PLA2 assay system. Inhibitory activity was associated with a 35-45000 dalton molecular weight fraction, heat-labile, sensitive to protease degradation and did not partition into organic solvents. These data are indicative that PLA2-inhibitory activity resides in a protein moiety. Dixon-plot analysis of myometrial-inhibitory activity was indicative that the inhibition of PLA2 activity was of a non-competitive nature (Ki = 4.1 +/- 0.7 micrograms/ml, ca 118 nmol/l). Myometrial phospholipase-inhibitory protein(s) may be involved in the suppression of eicosanoid biosynthesis by the uterine tissues throughout gestation thus inhibiting uterine contractile activity.
Insights
Pregnant ewe myometrium contains a heat-labile protein that inhibits phospholipase A2 (PLA2) activity. This non-competitive inhibition may suppress uterine contractions during gestation.
Area of Science:
- Biochemistry
- Reproductive Biology
- Enzymology
Background:
- The myometrium, or uterine muscle, plays a critical role in pregnancy and parturition.
- Eicosanoids are potent signaling molecules involved in uterine contractility.
- Phospholipase A2 (PLA2) is a key enzyme in the biosynthesis of eicosanoids.
Purpose of the Study:
- To identify and characterize factors within the pregnant ewe myometrium that modulate phospholipase A2 (PLA2) activity.
- To investigate the potential role of myometrial PLA2 inhibitory activity in regulating uterine function during gestation.
Main Methods:
- Myometrium samples were collected from pregnant ewes at 30-80 days of gestation.
- An in vitro porcine pancreatic PLA2 assay system was used to assess inhibitory activity.
- Fractionation, heat treatment, protease sensitivity, and solvent partitioning were employed to characterize the inhibitory moiety.
- Dixon-plot analysis was used to determine the type of enzyme inhibition.
Main Results:
- A factor inhibiting PLA2 activity was detected in the pregnant ewe myometrium.
- The inhibitory activity was associated with a heat-labile protein fraction (35-45 kDa) sensitive to proteases.
- The inhibition was characterized as non-competitive, with a Ki of 4.1 ± 0.7 µg/ml (approximately 118 nmol/l).
Conclusions:
- Pregnant ewe myometrium contains a protein that non-competitively inhibits PLA2 activity.
- This myometrial PLA2-inhibitory protein may contribute to suppressing eicosanoid biosynthesis.
- Such suppression could be crucial for maintaining uterine quiescence throughout gestation, preventing premature contractile activity.