Expression and hormonal regulation of the high-density lipoprotein (HDL) receptor Scavenger Receptor Class B Type I messenger ribonucleic acid in therat ovary
Mp. Mclean et Tw. Sandhoff, Expression and hormonal regulation of the high-density lipoprotein (HDL) receptor Scavenger Receptor Class B Type I messenger ribonucleic acid in therat ovary, ENDOCRINE, 9(3), 1998, pp. 243-252
Since cholesterol delivery to the ovary is an essential regulated step in s
teroidogenesis, mRNA levels for the Scavenger Receptor Class B Type I (SR-B
I), a putative high-density lipoprotein receptor (HDL-R), were examined in
response to tropic hormones and the luteolytic agent prostaglandin F2 alpha
(PGF2 alpha), For this, the rat SR-BI cDNA was isolated and cloned. The re
sults of this investigation revealed that a single SR-BI mRNA transcript of
2.4 kb was highly expressed in the rat adrenal, ovary, and testis, The SR-
BI transcript was increased (twofold) in the immature rat ovary following p
regnant mare's serum gonadotropin (PMSG) administration and in the ovary, 8
d after ovulation, in response to stimulation by human chorionic gonadotro
pin (hCG). In the ovary 8 d following ovulation, basal ovarian SR-BI mRNA l
evels were elevated up to sixfold relative to the preovulatory SR-BI mRNA l
evels. Even with the enhanced basal level of SR-BI mRNA within the ovary, h
CG administration still resulted in a 2.5- (p < 0.025) and sevenfold (p < 0
.01) increase in the 2.4-kb transcript, 3 and 6 h postinjection, respective
ly. This increase corresponded to a 58% increase in serum progesterone, In
contrast, when PCF2 alpha was administered, SR-BI mRNA levels were signific
antly reduced (3.5-fold; p < 0.01) in concert with a fourfold reduction (p
<0.001) in serum progesterone secretion. Furthermore, PCF2a blocked the hCG
-induced increase in SR-BI mRNA levels when administered 30 min prior to hC
G injection. The results of this study demonstrate that SR-BI mRNA levels a
re dramatically increased following exposure to gonadotropins in the ovary,
whereas PGF2a exposure significantly reduced SR-BI mRNA levels.