| Summary: | These studies examined the effects of prostaglandin-F[sub 2a] (PGF[sub 2a]) on progesterone and
178-estradiol (estradiol) production, as well as DNA and PGF[sub 2a]-receptor (PGF[sub 2a]-R) mRNA
levels, in the human granulosa-luteal cell (GLC). Additionally, the interactions of PGF[sub 2a] with human chorionic gonadotrophin (hCG), gonadotrophin-releasing hormone (GnRH) and prostaglandin E₂ (PGE₂) were examined, with respect to progesterone and estradiol production. In one study, cells were collected from small (<12 mm) and large (>12 mm) follicles separately,
permitting the examination of follicle size-dependent alterations in steroidogenesis.
Pharmacological techniques were utilized to elucidate the signal transduction pathways involved in the anti-gonadotrophic effects of PGF[sub 2a]. Moreover, these experiments were performed on GLCs cultured for one (D₁), eight (D₈) and/or twelve to fourteen days (D₁₂₋₁₄), in order to reveal culture
time-dependent alterations in cellular response.
Briefly, GLCs collected from patients undergoing in vitro fertilization (IVF), were cultured for the time periods described above, followed by a 24 h treatment period. After the treatment period media were collected and assayed for progesterone and estradiol, while cells were extracted
for DNA or total RNA.
It was found that human GLC responses to PGF[sub 2a] are culture time- and oncentrationdependent, with PGF[sub 2a] being either luteolytic or luteotrophic, depending on culture and treatment conditions. Moreover, GLC responses to hCG and PGF[sub 2a] varied with follicle size, suggesting that
these hormones' actions are targeted toward more mature follicles. Furthermore, GnRH potentiates the luteolytic effects of PGF[sub 2a], while it acts as a permissive factor for the luteotrophic effects. A complex interaction between PGF[sub 2a] and PGE₂ was also seen. The luteolytic effects of PGF[sub 2a] are
mediated through a pertussis toxin-sensitive G-protein (possibly G[sub i], G[sub p] or both). PGF[sub 2a] inhibits cholera toxin-, isoproterenol- and forskolin-, but not db-cAMP-stimulated progesterone production suggesting that this G-protein is exerting its actions on the adenylate cyclase pathway at the level of
adenylate cyclase, but not distal to it. Additionally, PGF[sub 2a] is capable of autoregulating its receptor mRNA levels, and thus its ability to regulate steroidogenesis in the human GLC. Prostaglandin F[sub 2a]-RmRNA levels were found to be inversely related to progesterone and estradiol production.
In conclusion, PGF[sub 2a] is a multi-functional hormone which acts through complex signal
transduction pathways and interactions with confounding hormones, to exert both luteotrophic and luteolytic effects.
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