Ripening of the rat cervix involves widespread collagenolysis that follows
an eosinophilic leukocyte infiltration. The hormonal control of these event
s is not well understood. The aims of this study were to investigate the me
chanism through which progesterone (P) and 17 beta-estradiol (E-2) modulate
eosinophilic invasion and to determine if this event is protein synthesis
mediated. Cervical eosinophilic invasion was measured in intact rats during
the second half of pregnancy and compared with values from ovariectomized
(O) pseudopregnant (PSP) rats treated with P and E-2 in doses that mimicked
the levels of pregnancy. Other O-PSP rats were treated with an E-2 antagon
ist (tamoxifen) and the antiprogestin RU-486. To study the role of protein
synthesis in eosinophilic invasion of the cervix, rats were treated with ac
tinomycin-D (an inhibitor of mRNA synthesis), and animals were sacrificed o
n D21 or D22 to evaluate eosinophilic invasion. Rats treated with E-2 showe
d high levels of infiltration and tamoxifen blocked this E-2 effect. On the
other hand, P antagonized the stimulatory effects of E-2 on eosinophilic i
nvasion, however when the P and E-2 treated rats were injected with RU-486
the inhibitory effect of P was reversed. In intact pregnant rats a sharp ri
se in eosinophilic infiltration was detected on D23, 20 h after the fall of
serum P. Finally, E-2 treated rats injected with actinomycin-D had no inva
sion of eosinophils. In conclusion, the estrogen-triggered eosinophil invas
ion is affected by the classic estrogen receptor antagonist tamoxifen and b
y the mRNA synthesis blocker actinomycin-D suggesting a genomic action of E
-2. Furthermore, the estrogen effect is blocked by P and this inhibition is
reversed by RU-486. (C) 2000 Elsevier Science Inc. All rights reserved.