Effect of ETBE on reproductive steroids in male rats and rat Leydig cell cultures

These experiments were conducted to follow up on a report of testis seminiferous tubular degeneration in Fischer 344 rats treated with high doses of ethyl t-butyl ether (ETBE). Also, high doses of a related compound, methyl t-butyl ether (MTBE), had been shown to reduce circulating testosterone (T) in rats. Isolated rat Leydig cells were used to compare hCG-stimulated T production following exposure to ETBE, MTBE, and their common main metabolite, TBA. In addition, male Fischer 344 rats were gavaged daily with 600 mg/kg, 1200 mg/kg or 1800 mg/kg ETBE in corn oil (n = 12) for 14 days, the 1200 mg/kg dose chosen for comparison with a prior 14-day MTBE gavage experiment. In cell culture experiments, TBA was more potent than either ETBE or MTBE, both of which caused similar inhibition of T production at equimolar concentrations. In the in vivo study, no significant plasma T reduction was seen 1 h after the final 1200 mg/kg ETBE dose, whereas 1200 mg/kg MTBE had significantly lowered T when administered similarly to Sprague–Dawley rats. Some rats treated with 1800 mg/kg ETBE had noticeably lower T levels, and the group average T level was 66% of corn oil vehicle control (p > 0.05) with high variability also evident in ETBE-treated rats. 17β-Estradiol had been increased by 1200 mg/kg MTBE, and was elevated in the 1200 and 1800 mg/kg ETBE dose groups (p < 0.05), both groups also experiencing significantly reduced body weight gain. None of these effects were seen with 600 mg/kg/day ETBE. No definitive evidence of androgen insufficiency was seen in accessory organ weights, and no testicular pathology was observed after 14 days in a small subset of 1800 mg/kg ETBE-treated animals. Like MTBE, ETBE appears to be capable of altering reproductive steroid levels in peripheral blood sampled 1 h after treatment, but only with extremely high doses that inhibit body weight gain and may produce mortality.