Effects of Mono(2-Ethylhexyl) Phthalate, a Testicular Toxicant, on Follicle-Stimulating Hormone Binding to Membranes from Cultured Rat Sertoli Cells1

The widely used plasticizer di(2-ethylhexyl) phthalate (DEHP) is a male reproductive toxicant. Its toxicity has been shown to be due primarily to the action of its metabolite mono(2-ethylhexyl) phthalate (MEHP) on Sertoli cells. We have previously shown that at least one of the sites of action of MEHP on the Sertoli cell is the cAMP second messenger system. MEHP inhibits the ability of FSH but not isoproterenol, forskolin, or cholera toxin to stimulate cAMP accumulation in cultured Sertoli cells in a dose- and time-dependent manner. To further characterize this effect of MHP, we prepared a light membrane fraction from control and MEHP-treated Sertoli cells cultured from 18-day-old Fischer 344 rats and measured FSH binding in a radioligand receptor assay using 125I-labeled human FSH (125I-hFSH). MEHP inhibited FSH binding when preincubated with Sertoli cells in culture but not when added simultaneously with 125I-hFSH to the purified membrane preparation. Attenuation of FSH binding was evident after a 3-h preincubation with 100 μM MEHP (18%) and was maximal after 15–24 h of preincubation (70–90%). Preincubation of Sertoli cells for 24 h with 100 μM DEHP had no effect on FSH binding. Half-maximal inhibition occurred at approximately 0.1 μM MEHP. Scatchard analysis indicated a four-fold decrease in FSH affinity with no change in receptor concentration. Exposure of Sertoli cells to MEHP amplified the attenuating effect of guanosine triphosphate (GTP) on FSH binding, suggesting that the action of MEHP may be at the level of the GTP-binding protein that couples the FSH receptor to the adenylate cyclase catalytic subunit.This effect of MEHP is age-independent over the range of 18–45 days. The active metabolites of the other phthalates toxic in vivo, i.e., monobutyl phthalate and monopentyl phthalate, also reduced FSH binding to Sertoli cell membranes but only from the older animals. Monomethyl phthalate, which is not a testicular toxicant in vivo, had no effect on FSH binding from animals at any age tested. We conclude that the ability of certain phthalate esters to reduce FSH binding to Sertoli cell membranes is likely to be at least a part of the mechanism responsible for their testicular toxicity.