Hydroquinone: A Developmental Toxicity Study in Rats

To determine the potential developmental toxicity of hydroquinone(HQ), pregnant rats (COBS-CD-BR) were given 0, 30, 100, or 300mg/kg HQ by gavage on the 6th through the 15th days of gestation.Maternal effects included a slight, but significant (p 0.05),reduction in body weight gain and feed consumption for the 300mg/kg HQ dams. Reproductive indices, i.e., pregnancy rate, numbersof corpora lutea, implantation sites, viable fetuses, and earlyand late resorptions, fetal sex ratio, pre-and postimplantationlosses, and gravid uterine weights, were not affected by treatmentwith HQ. A slightly reduced (p 0.05) mean fetal body weightseen at the 300 mg/kg dose level was associated with the slightlyreduced body weight gain seen for the dams at this dose level.Gross external, internal soft tissue, and skeletal examinationsof the fetuses revealed no HQ-related malformations. The incidencesof gross external variations (small hematomas) and internalsoft tissue variations (dilated renal pelvis, hydronephrosis,and hydroureter) in the HQ-treated litters were not statisticallydifferent from the control incidences. Skeletal variations (delayedossification of membranous skull bones, hyoid bone, thoraciccentra 1–3, sacral arches 3 and 4, and bilobed thoraciccentra 9–13) were seen with similar frequency in the controland HQ-treated groups. A statistically significant increasein the incidence of total common vertebral variations seen atthe 300 mg/kg HQ dose level was not considered toxicologicallysignificant. The incidences of total skeletal variations werenot statistically different between the control and the HQ-treatedgroups. It is concluded that HQ was not selectively toxic tothe developing rat conceptus and, thus, appears not to havethe properties of a developmental toxicant. The no-observable-effectlevel for both maternal and developmental toxicity was 100 mg/kg,whereas 300 mg/kg was the no-observable-adverse-effect level.