AJP - Endocrinology and Metabolism, Vol 258, Issue 5 E740-E747, Copyright © 1990 by American Physiological Society
PGF2 alpha and PGE2 binding to rat myometrium during gestation, parturition, and postpartum
M. Molnar and F. Hertelendy
Department of Obstetrics and Gynecology, St. Louis University School of Medicine, Missouri 63104.
The specific binding of prostaglandins (PG) F2 alpha and E2 was studied in
a rat myometrial membrane-enriched fraction during the latter part of
gestation and parturition, as well as in the postpartal period. Tritiated
PGE2 and PGF2 alpha binding was specific, saturable, time dependent, and
directly proportional to the amount of membrane protein. Scatchard analysis
indicated the presence of high-affinity (Kd2) and low-affinity (Kd2)
binding sites for both PGs. The affinity of both binding sites for PGF2
alpha and the apparent Kd2 for PGE2 remained essentially the same
throughout gestation and post-partially and were similar to nonpregnant
rats. The apparent Kd1 of PGE2, however, increased by 10-fold from day 21
of gestation to 1 day postpartum. Although the maximal binding capacity of
the high-affinity (Bmax1) and low-affinity (Bmax2) binding sites of PGF2
alpha showed a nonsignificant increase compared with prepartum values,
reaching maximal values 12-24 h postpartum, those of PGE2 showed a
significant increase on the third day after delivery. The concentration of
prostanoids in uterine venous plasma and amniotic fluid increased
significantly with approaching parturition, whereas plasma progesterone
decreased, raising the estradiol-progesterone ratio 25-fold. After
unilateral fetectomy, the binding sites for PGF2 alpha and PGE2 increased
significantly compared with the contralateral pregnant horns.
Administration of the PG synthetase inhibitor, indomethacin, also increased
two- to threefold both PGF2 alpha and PGE2 binding compared with the
placebo group, whereas intrauterine administration of PGF2 alpha and PGE2
significantly reduced it.(ABSTRACT TRUNCATED AT 250 WORDS)
