Suppression of testosterone production by nanoparticulate TiO<sub>2</sub> is associated with ERK1/2-PKA-PKC signaling pathways in rat primary cultured Leydig cells.
Further experiments proved that FFA1 couples to a Gq protein and activates PI-PLC, which induces the IP3/Ca<sup>2+</sup> and DAG/PKC signal pathways, both of which are involved in ERK1/2 activation.