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Platelet-activating factor (PAF) is a product of the embryo and theendometrium in early pregnancy. The actions of PAF may be regulated by itsdegradation 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 theendometrium and uterine fluid of mice during early pregnancy. The enzymeactivity from uterine endometrium and luminal fluids had the same biochemicalcharacteristics as the plasma form of the enzyme. The three sources of enzymeactivity (i) had an apparent native molecular massgreater than 106 Da, but this was reduced afterdetergent treatment and purification to 60-65 kDa;(ii) bound to cholesterol hemisuccinate agarose matrix;and (iii) were found in the high densitylipoprotein-enriched fraction after density gradient ultracentrifugation. Incastrate females, oestradiol-17&bgr; (E<emph type="8">2) caused adose-dependent increase in the activity of the enzyme in endometrium andluminal fluid. Progesterone (P<emph type="8">4) inhibited theE<emph type="8">2-induced increase in PAF:ah in uterine tissue.Treatment with E<emph type="8">2 alone caused an increase inendometrial PAF:ah activity within 24 h, which declined within 48 h. Inluminal fluid, the same treatment caused increased activity within 24 h,peaking after 48 h of treatment and then declining. InE<emph type="8">2-treated castrate females, mRNA for an intracellular(but not plasma) form of PAF:ah was detected, yet the intracellular form wasnot detected biochemically. The results suggest that most of the enzymeactivity was not produced locally, but probably resulted from the influx ofthe plasma form of the enzyme.Extra keywords: enzyme, oestradiol 17-&bgr;,progesterone. |
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