Human Reproduction, Vol 12, 2748-2755, Copyright © 1997 by Oxford University Press
YX Liu, XR Peng, YJ Chen, W Carrico and T Ny
This study was conducted to determine whether prolactin (PRL) suppresses
gonadotrophin-induced ovulation and disturbs the co- ordinated gene
expression of tissue type plasminogen activator (tPA) and plasminogen
activator inhibitor type-1 (PAI-1) in rat ovary. Immature female rats were
injected with 10 IU pregnant mare's serum gonadotrophin to stimulate
follicle growth, and 48 h received different doses of prolactin followed by
7 IU human chorionic gonadotrophin (HCG). The oviducts were examined for
the presence of ova, and the amounts of tPA and PAI-1 mRNA present in the
ovary were measured at various times after the hormone treatment. PRL had
no significant effect on ovarian weight but caused a dose-dependent
decrease in ovulation number. In the control animals receiving HCG alone,
13.3 +/- 1.3 (mean +/- SEM) ova/oviduct were found; while in animals
receiving HCG plus 50, 100 or 200 microg PRL, the ovulation number was
dose- dependently suppressed by 53.6, 66.9 and 76% respectively at 18 h
after treatment. PRL suppression of HCG-induced ovulation was
time-dependent. By 24 h after treatment, the number of ova in the oviducts
in HCG- and HCG plus PRL-treated groups was not significantly different.
PRL also suppressed HCG-induced tPA gene expression in a dose- and time-
dependent manner. At all time points examined, tPA mRNA content of whole
ovaries and granulosa cells (GC) in PRL-treated groups was lower than in
the HCG-treated controls. The activities of PAI-1 in ovarian extracellular
fluid (OEF) and PAI-1 mRNA in the theca-interstitial cells (TI) in the
PRL-treated groups were higher than in the HCG- treated controls. The
highest stimulation by PRL of PAI-1 activity in OEF and of PAI-1 mRNA in TI
was observed at 9 h and 6 h after HCG treatment respectively. The
localization of tPA and PAI-1 antigens in the ovaries was consistent with
changes in the mRNA and activity levels. These data suggest that PRL
temporarily delays, but does not completely inhibit, HCG-induced ovulation,
which may be caused by a suppression of PA-mediated proteolysis.
ARTICLES
Prolactin delays gonadotrophin-induced ovulation and down-regulates expression of plasminogen-activator system in ovary
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Sciences, Beijing.
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