Gonadotropin Surge-Attenuating Factor: A Nonsteroidal Ovarian Hormone Controlling GnRH-Induced LH Secretion in the Normal Menstrual Cycle.

Gonadotropin surge-attenuating factor (GnSAF) is a nonsteroidal ovarian substance, which attenuates the endogenous LH surge in superovulated women. Different molecular sequences have been found, but only one of them has shown substantial homology to a known substance of the human genome. A molecular mass of 12.5kDa showing identity to the carboxyl-terminal fragment of human serum albumin and expressing GnSAF bioactivity in vitro has been identified. It has been suggested that in the normal menstrual cycle the in vivo bioactivity of GnSAF increases under the influence of the intercycle rise of FSH. GnSAF is considered the "missing link" between the ovaries and the hypothalamo-pituitary system, maintaining the pituitary in a state of low responsiveness to GnRH in the early- to midfollicular phase of the cycle. A marked decline in GnSAF bioactivity in the late follicular phase facilitates the onset and the full expression of the midcycle LH surge.

Naturally occurring steroids in Xenopus oocyte during meiotic maturation. Unexpected presence and role of steroid sulfates.

In the ovary, oocytes are surrounded by follicle cells and arrested in prophase of meiosis I. Although steroidogenic activity of follicle cells is involved in oogenesis regulation, clear qualitative and quantitative data about the steroid content of follicles are missing. We measured steroid levels of Xenopus oocytes and follicles by gas chromatography-mass spectrometry. We show that dehydroepiandrosterone sulfate is the main steroid present in oocytes. Lower levels of free steroids are also detected, e.g., androgens, whereas progesterone is almost undetectable. We propose that sulfatation is a protective mechanism against local variations of active steroids that could be deleterious for follicle-enclosed oocytes. Steroid levels were measured after LH stimulation, responsible for the release by follicle cells of a steroid signal triggering oocyte meiosis resumption. Oocyte levels of androgens rise slowly during meiosis re-entry whereas progesterone increases abruptly to micromolar concentration, therefore representing the main physiological mediator of meiosis resumption in Xenopus oocyte.

Purification of a candidate gonadotrophin surge-inhibiting/attenuating factor (GnSIF/AF) showing MAPK as a possible target.

Gonadotrophin surge-inhibiting/attenuating factor (GnSIF/AF) has been known for over two decades, but its molecular structure has not been completely characterized yet. In the last 20 years, five different putative GnSIF/AF sequences have been published. In this article, we describe a procedure to isolate and characterize GnSIF/AF from bovine follicular fluid, a GnSIF/AF-derived synthetic peptide (SP-GnSIF/AF) was produced, and the intracellular bioactivity of GnSIF/AF was tested for intracellular action with a MAPK-assay. Two different bioactive molecular weight forms of GnSIF/AF were isolated, a 160 kDa heteromeric and a monomeric 40 kDa protein. The 40 kDa form appeared to be a subunit of the 160 kDa protein. The synthetic peptide mimicked the actions of GnSIF/AF, such as inhibition of GnRH-induced LH secretion and attenuation of the MAPK phosphorylation. The two GnSIF/AF candidates do not show similarities with previously published GnSIF/AF sequences. These are the first data showing the influence of GnSIF/AF on intracellular processes involved in GnRH self-priming and that the biological action of GnSIF/AF was preserved in the produced synthetic peptide. The results provide strong evidence that the identified candidate proteins are the true GnSIF/AF.

Removal of natural hormones by nanofiltration membranes: measurement, modeling, and mechanisms.

The removal mechanisms of four natural steroid hormones-estradiol, estrone, testosterone, and progesterone-by nanofiltration (NF) membranes were investigated. Two nanofiltration membranes with quite different permeabilities and salt retention characteristics were utilized. To better understand hormone removal mechanisms, the membrane average pore size was determined from retention data of inert organic solutes of various molecular weights and a pore transport model that incorporates steric (size) exclusion and hindered convection and diffusion. Results indicate that, at the early stages of filtration, adsorption (or partitioning) of hormones to the membrane polymer is the dominant removal mechanism. Because the adsorptive capacity of the membrane is limited, the final retention stabilizes when the adsorption of hormones into the membrane polymer has reached equilibrium. At this later filtration stage, the overall hormone retention is lower than that expected based solely on the size exclusion mechanism. This behavior is attributed to partitioning and subsequent diffusion of hormone molecules in the membrane polymeric phase, which ultimately results in a lower retention. Hormone diffusion in the membrane polymeric matrix most likely depends on the size of the hormone molecule, hydrogen bonding of hormones to membrane functional groups, and hydrophobic interactions of the hormone with the membrane polymeric matrix.