Binding and degradation of doubly radioiodinated luteinizing hormone by mouse Leydig cells

Adipokines Expression and Effects in Oocyte Maturation, Fertilization and Early Embryo Development: Lessons from Mammals and Birds

Some evidence shows that body mass index in humans and extreme weights in animal models, including avian species, are associated with low in vitro fertilization, bad oocyte quality, and embryo development failures. Adipokines are hormones mainly produced and released by white adipose tissue. They play a key role in the regulation of energy metabolism. However, they are also involved in many other physiological processes including reproductive functions. Indeed, leptin and adiponectin, the most studied adipokines, but also novel adipokines including visfatin and chemerin, are expressed within the reproductive tract and modulate female fertility. Much of the literature has focused on the physiological and pathological roles of these adipokines in ovary, placenta, and uterine functions. The purpose of this review is to summarize the current knowledge regarding the involvement of leptin, adiponectin, visfatin, and chemerin in the oocyte maturation, fertilization, and embryo development in both mammals and birds.

Endocytosis of lutropin by Leydig cells through a pathway distinct from the high-affinity receptor

In porcine Leydig cells in primary culture, 95% of the internalization of [125I]porcine lutropin ([125I]pLH, which bears sulfated GalNAc) could not be ascribed to the high-affinity LH receptor (LHR). In contrast, >40% of [125I]human choriogonadotropin (hCG, with sialylated sugar chains) uptake was performed by the LHR itself. When the LHR was down-regulated by excess unlabeled hormone, the LHR-independent incorporation of [125I]pLH could be inhibited in a dose-dependent fashion by sulfated polysaccharides such as fucoidan or chondroitin-(4 or 6)-sulfate, but not by other polyanionic compounds, nor by sulfated chondroitin disaccharides. Endocytosis occurred through a clathrin-dependent pathway and was inhibited by low temperature, endocytosis inhibitors, increased ionic strength, or by EDTA and dithiothreitol. Taken together, these results suggest that a Leydig cell membrane protein (possibly a lectin, or a glycosaminoglycan receptor) could perform specific LH clearance in the testis via recognition of its sulfated sugars.

Ultrastructural immunoperoxidase investigations of HCG binding to isolated testicular intertubular cells

The binding and processing of human chorionic gonadotrophin (HCG) on isolated rat testicular intertubular cells was investigated using an ultrastructural immunoperoxidase technique. Following incubation of isolated cells with HCG at a range of temperatures and time intervals, cells were fixed and the presence of HCG demonstrated using monoclonal and polyclonal antibodies to HCG and its alpha and beta subunits. Results indicated that HCG binds to the surface of the Leydig cells where it is rapidly split into its component subunits. Internalization of the HCG molecule was not demonstrated. The testicular macrophages also bound HCG. In contrast to the Leydig cells they were able to internalize the molecule into lysosomes in the cytoplasm. The complete molecule and the alpha and beta subunits were found within the cells. The study suggests that results of previous studies using mixed populations of isolated cells may be due to the combined effects of the different mechanisms present in the two cell types. It is postulated that Leydig cells bind HCG on the surface and cyclic AMP is activated prior to breakdown and loss of the hormone from the surface of the cells. It is postulated that the macrophages play a role in the breakdown of excess trophic hormone and act in concert with the Leydig cells in the local control of testicular function.