EFFECTS OF AMMONIUM PERFLUOROOCTANOATE ON LEYDIG-CELL FUNCTION - IN-VITRO, IN-VIVO, AND EX-VIVO STUDIES

Ammonium perfluorooctanoate (C8) produced a dose-dependent increase in Leydig cell adenomas in Crl:CD BR (CD) rats fed 0, 30, or 300 ppm for 2 years. Administration of C8 to adult male CD rats, by gavage for 14 days, produced decreased serum and testicular interstitial fluid testosterone levels and increased serum estradiol levels. The C8-mediated decrease in the serum testosterone levels appeared to be due to a lesion at the level of the testis. These endocrine changes may play a role in the C8 induction of Leydig cell tumors. In the present work, C8 was examined for its ability to (1) directly affect Leydig cells in vitro using isolated Leydig cells from untreated rats and ex vivo using Leydig cells isolated from C8-treated rats, (2) affect testicular interstitial fluid hormone levels, and (3) induce aromatase activity. These studies were conducted to investigate the hypothesis that C8 produces an increase in estradiol by inducing cytochrome P450 XIX (aromatase), which converts testosterone to estradiol, and that the elevated estradiol levels ultimately produce Leydig cell hyperplasia and adenoma formation by acting as a mitogen or enhancing growth factor secretion. In the in vivo and ex vivo studies, adult male CD rats were gavaged with either 0 or 25 mg/kg/day C8 for 14 days. In addition to the an libitum control, a second control group was pair-fed to the 25 mg/kg/day C8 group. In the in vitro and ex vivo studies, Leydig cells were isolated from testes of adult males by collagenase digestion followed by enrichment over Percoll gradients. A dose-dependent decrease in testosterone levels was observed in hCG-stimulated Leydig cells treated in vitro with C8 for 5 hr (IC50 approximately 200 mu M). In contrast, ex vivo studies demonstrated an increase in testosterone production in hCG-stimulated Leydig cells from C8-treated rats when compared to Leydig cells isolated from either the ad libitum or pair-fed control rats. The in vitro data demonstrate that C8 directly inhibits testosterone release from Leydig cells, while the ex vivo data demonstrate that this inhibition is reversible. In the in vivo study, serum and testicular interstitial fluid estradiol concentrations were significantly higher in the C8-treated rats when compared to the pair-fed control group. In addition, testicular interstitial fluid transforming growth factor alpha (TGF alpha) levels were also increased, consistent with the hypothesis that estradiol may modulate growth factor expression within the testis. In a follow-up in vivo study, C8 produced a 4.5-fold increase in hepatic aromatase when compared to the pair-fed control, but did not increase aromatase activity in the testis, muscle, or fat. Collectively, these data suggest that the increase in serum estradiol levels the liver. (C) 1995 Academic Press, Inc.