Gonadotroph cells in the anterior pituitary gland produces luteinizing hormone (LH) and follicle-stimulating hormone (FSH), and play important roles in the function of reproduction. Hypothalamic neurons secrete gonadotropin-releasing hormone (GnRH) and regulate the release of LH and FSH from gonadotroph cells. In fact, high-frequency GnRH pulse induces the release of LH from the gonadotroph cells, whereas low-frequency GnRH pulse induces the release of FSH from the cells. However, the precise release mechanism of LH and FSH from the gonadotroph cells have only partly understood.
In the present study, we used a mouse derived LβT2 cells as a gonadotroph cell model to elucidate the release mechanism of LH and FSH. We transfected fluorescent protein (FP)-tagged LH and FSH into the LβT2 cells and determined the cellular distributions of those under confocal microscopy. We found that LH-FP and FSH-FP were well colocalized with each other. We next observed the release dynamics of LH-FP and FSH-FP-containing vesicles by using the total internal reflection microscopy. Application of 30 nM GnRH to the cells induced the rapid increase of fluorescence intensity of both LH-FP and FSH-FP-containing vesicles. Although LH-FP-containing vesicles showed rapid disappearance (within 1 s) after the increase of its fluorescence intensity, FSH-FP-containing vesicles gradually dimmed (within 10 s). These results suggest that the different release dynamics of LH and FSH might be associated with the GnRH pulse frequency-dependent LH and FSH release from the cells.