The measurement of phospholipase A2 activity in human myometrium: physiological and pathological implications

Phospholipase A2 activity was measured in human myometrium obtained at hysterectomy in a group of 41 patients using a double isotope ratio assay based on the liberation of [14-C] oleic acid from 1-palmitoyl-2-[14-C] oleoyl phosphatidylcholine. The enzyme was shown to be calcium independent and to have an optimum pH of 7. There was no significant difference (Mann Whitney U test) in myometrial phospholipase A2 activity between proliferative and secretory phases of the menstrual cycle (ranges: 3.88-30.8 and 0.47-25.85 nmol/mg protein per h respectively) but there was a significant (P less than 0.01) increase in activity in myometrium from uteri with fibroids (median 11.33, range 2.18-30.88 nmol/mg protein per h) compared to those without fibroids (median 6.94, range 0.31-25.85 nmol/mg protein per h). Myometrial phospholipase A2 activity was significantly lower (P less than 0.001) in the 33-40 age group (median 4.71, range 0.31-6.94) compared to the 41-50 age group (median 11.35, range 2.18-30.88 nmol/mg protein per h). In the 51-55 age group phospholipase A2 activity (median 8.71, range 2.5-17.71 nmol/mg protein per h) was not significantly different from that of the other two groups. The increase in activity in the 41-50 age group was not due to the increased incidence of uterine fibroids. These findings suggest that myometrial phospholipase A2 may be important in the pathophysiology of the uterus.