Identification and regulation of the platelet-activating factor acetylhydrolase activity in the mouse uterus in early pregnancy

Abstract

Platelet-activating factor (PAF) is a product of the embryo and the endometrium in early pregnancy. The actions of PAF may be regulated by its degradation and this is largely achieved by the enzyme PAF acetylhydrolase (PAF:ah; EC 3.1.1.47). The present study characterized the PAF:ah in the endometrium and uterine fluid of mice during early pregnancy. The enzyme activity from uterine endometrium and luminal fluids had the same biochemical characteristics as the plasma form of the enzyme. The three sources of enzyme activity (i) had an apparent native molecular mass greater than 10⁶ Da, but this was reduced after detergent treatment and purification to 60–65 kDa; (ii) bound to cholesterol hemisuccinate agarose matrix; and (iii) were found in the high density lipoprotein-enriched fraction after density gradient ultracentrifugation. In castrate females, oestradiol-17β (E₂) caused a dose-dependent increase in the activity of the enzyme in endometrium and luminal fluid. Progesterone (P₄) inhibited the E₂-induced increase in PAF:ah in uterine tissue. Treatment with E₂ alone caused an increase in endometrial PAF:ah activity within 24 h, which declined within 48 h. In luminal fluid, the same treatment caused increased activity within 24 h, peaking after 48 h of treatment and then declining. In E₂-treated castrate females, mRNA for an intracellular (but not plasma) form of PAF:ah was detected, yet the intracellular form was not detected biochemically. The results suggest that most of the enzyme activity was not produced locally, but probably resulted from the influx of the plasma form of the enzyme.