Progestin regulation of progesterone biosynthetic enzymes in cultured rat granulosa cells

Progestins have recently been shown to augment gonadotropin-stimulated progesterone and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OH-P) biosynthesis in cultured rat granulosa cells. The mechanism by which progestins autoregulate ovarian progestin biosynthesis was investigated by studying the modulation of pregnenolone biosynthesis as well as the activities of the enzymes 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) and 20 alpha-hydroxysteroid dehydrogenase (20 alpha-HSD). Granulosa cells obtained from immature hypophysectomized, estrogen-treated rats were cultured with FSH and/or progestins. Pregnenolone production was measured in the presence of cyanoketone (10(-6) M) to inhibit 3 beta-HSD activity. Enzymatic activities of 3 beta-HSD and 20 alpha-HSD were determined in cell homogenates by direct enzyme assays. FSH stimulated pregnenolone production, while treatment with progesterone or R5020 alone was ineffective. Concomitant treatment with the progestins further enhanced FSH-stimulated pregnenolone production in a dose-dependent manner with minimal effective doses of 10(-8) and 10(-7) M for R5020 and progesterone, respectively. In FSH-primed cells, LH increased pregnenolone accumulation, and concomitant treatment with R5020 also enhanced the LH action. Furthermore, the gonadotropins stimulated the activity of 3 beta-HSD, and this effect was further enhanced by concomitant treatment with either R5020 or progesterone in a dose-dependent manner. In addition, the 20 alpha-HSD activities were enhanced by progestins in cells treated with FSH but not with LH. Thus, both natural and synthetic progestins stimulate the gonadotropin-induced progesterone production in cultured granulosa cells via enhancing the 3 beta-HSD enzyme as well as pregnenolone biosynthesis.     

Fibroblast growth factor as an intraovarian hormone: differential regulation of steroidogenesis by an angiogenic factor

The potential role of fibroblast growth factor (FGF) in the regulation of granulosa cell differentiation was investigated because of its recent identification as the corpus luteum angiogenic factor. Treatment of rat ovarian granulosa cells with FGF inhibits the capacity of follicle stimulating hormone to stimulate estrogen production and to induce luteinizing hormone receptors. In contrast, although incubations with FGF can inhibit the estrogen-sensitive component of progesterone synthesis, the presence of FGF with suboptimal concentrations of follicle stimulating hormone significantly enhances the synthesis of progesterone. This capacity to differentially regulate steroidogenesis in the granulosa cell is comparable to the potency of FGF (ED50 = 30 pg/ml, 10(-12) M) in other in vitro assays. The observation that an angiogenic factor, like FGF, can specifically increase the sensitivity of progesterone synthesis and simultaneously inhibit estrogen formation supports the hypothesis that this growth factor plays an important role in the development and maintenance of a functional corpus luteum. As such, FGF may be involved in the local regulation of follicular selection, growth and atresia by simple virtue of its capacity to induce a neovascular response on one hand and by its ability to modulate the differentiated response to gonadotropins on the other.     

Effect on an antagonistic analog of gonadotropin releasing hormone upon ovarian granulosa cell function.

We have recently demonstrated that gonadotropin releasing hormone (GnRH) acts directly on ovarian granulosa cells to inhibit the follicle stimulating hormone (FSH)-induced increase in granulosa cell steroidogenesis $\text{in}$$\text{vitro}$. A GnRH antagonist, [D-pGlu¹, D-Phe², D-Trp^3,6] GnRH (A), which is known to antagonize GnRH-stimulated gonadotropin release by cultured pituitary cells, was tested in the granulosa cell system. GnRH (10^?8M) inhibited estrogen and progesterone production by FSH-treated granulosa cells $\text{in}$$\text{vitro}$, whereas the antagonist A (10^?6M) did not affect FSH stimulation of steroidogenesis. Antagonist A, when added together with GnRH and FSH, blocked the GnRH inhibition of FSH-induced steroidogenesis. Estrogen and progesterone production by granulosa cells was increased by 50% at a molar ratio (IDR₅₀) of $\text{20}\text{1}\text{and}\text{12}\text{1}$ ([antagonist]/[GnRH]), respectively. At 10^?6M, antagonist A completely prevented the GnRH (10^?8M) inhibition. A similar effect of antagonist A was seen in FSH-induced increase of luteinizing hormone (LH) receptor content. FSH treatment for 2 days $\text{in}$$\text{vitro}$ induced an 8-fold increase in LH receptor content in cultured granulosa cells; concomitant treatment with 10^?8M GnRH completely inhibited the FSH effect. Antagonist A (10^?6M), by itself, had no effect on the FSH action. However, when added together with FSH and GnRH, antagonist A completely abolished the inhibitory effect of GnRH. These results demonstrate that the direct inhibitory effect of GnRH on granulosa cell function can be prevented by a GnRH antagonist and that the GnRH action at the ovarian level may require stringent stereospecific interactions of these peptides with putative GnRH recognition sites.     

Gonadotropin-releasing hormone: molecular and cell biology, physiology, and clinical applications

The observations in recent years that gonadotropin-releasing hormone ( pyroGlu1 -His2-Trp3- Ser4 -Tyr5- Gly6 -Leu7-Arg8-Pro9- G ly10NH2 [GnRH]) has considerable clinical efficacy as a contraceptive, an ovulation-inducing agent, and a drug that is useful in the therapy of a number of diseases are owed in no small part to advances that have been made in the basic molecular biology and physiology of this peptide. It is reasonable then that this symposium should be broken down into three separate yet integrated areas: 1) the molecular and cellular biology of GnRH, 2) the physiology of GnRH, and 3) the clinical efficacy of this compound. A number of recent advances have helped the progress of work in all three of these areas. The observation that substitution of a D-amino acid in the sixth amino acid position leads to considerable metabolic stability and reduced degradation of releasing hormone analogs has been especially useful. In addition, the observation that the further derivatization of such substituted compounds by deletion of the 10th amino acid and addition of an ethylamide group to Pro9 has resulted in compounds with a markedly increased ability to bind to the receptor. These compounds have been useful clinically and have allowed development of radioligand assays to be used in animal studies and in vitro. The availability of a large number of agonists and antagonists has allowed formulation of molecular models for GnRH and resulted in development of clinically useful compounds. In a short paper of this nature we cannot hope to provide an encyclopedic review; rather we hope to provide an overview and offer references to the literature for those who wish a more in-depth treatment.     

Endotoxin induces PAF production in the rat ileum: Quantitation of tissue PAF by an improved method

PAF (platelet-activating factor) is an endogenous mediator of endotoxin (LPS) shock and intestinal injury. In the present study we used an improved method to quantitate intestinal PAF after LPS injection. Both column and thin layer chromatography (TLC) were used to purify PAF. We found that using C18 column eluted sequentially with 10% acetic acid, ethyl acetate and 70% ethanol, yielded consitent results. TLC yielded falsely high PAF values, possibly from an unknown tissue lipid which co-migrated with PAF, or from toxic ingredients in the silica gel. Moreover, addition of optimal amounts of Tween-20 or ethanol in the bioassay samples enhanced PAF solubility and markedly improved PAF recovery. Lastly, dilution and heparinization of platelet-rich plasma greatly improved the sensitivity of the bioassay. The overall PAF recovery under these optimal conditions was 70–80%. We found that LPS (2–10 mg/kg, iv, 90 min) stimulated PAF production in the rat ileum, but not in the jejunum and colon. The difference in PAF production did not correlate to the numbers of sequestered neutrophils (reflected by myeloperoxidase levels) after LPS injection. This selective PAF production may account for the special vulnerability of the ileum to develop injury during endotoxemia.     

Studies of the optical properties of the proflavine–DNA complex

We report studies of the optical properties of the proflavine–DNA complex, using absorbance and circular dichroism spectroscopy. From comparison of the absorption spectra of proflavine complexed with calf thymus and T2 DNA, we conclude that stacking of the dyes external to the double helix is comparatively much weaker with T2 DXA, probably because of its glucosylation. Several sources are found for the circular dichroism induced in proflavine when it is complexed with DNA. There is a relatively weak circular dichroism induced when the dye is infinitely dilute on the DNA lattice; this presumably arises from the environmental asymmetry of the binding site. Stronger circular dichroism effects are induced by interaction of intercalated and stacked dyes; studies with T2 DNA, for which stacking seems to be blocked, permit a tentative resolution of effects due to the two modes of binding. One recurring theme of these studies is the observation that the optical properties are quite dependent on environment. The most dramatic example is a strong variation with salt concentration of the amplitude of the circular dichroism induced in the isolated (intercalated) monomer by the surrounding DNA. This suggests that the structure of the intercalated complex is quite sensitive to external conditions.