Study of the embryofoetotoxicity of alpha-terpinene in the rat.

alpha-Terpinene (1-isopropyl-4-methyl-1,3-cyclohexadiene) (TER) is a monoterpene found in the essential oils of a large variety of useful plants. Despite the widespread use of plants and essential oils containing TER in folk medicine potions and cosmetics, and as a flavouring food additive, toxicity studies of this monoterpene are scarce. The present study was undertaken to provide data on the embryofoetotoxic potential of TER in the rat. TER (30, 60, 125 and 250 mg/kg body weight) in corn oil was given by gavage to female Wistar rats from day 6 to 15 of pregnancy. Caesarean sections were performed on day 21 of pregnancy. The number of implantation sites, living and dead foetuses, resorptions and corpora lutea were recorded. All foetuses were weighed, examined for externally visible malformations, numbered with a marker pen and fixed in 5% formalin solution. One-third of the foetuses of each litter, chosen at random, were evaluated for visceral anomalies by a microsectioning technique. Heart, lungs, thymus, liver, spleen and kidneys of foetuses that were microdissected were also weighed. The remaining foetuses were examined for skeletal malformations after clearing with potassium hydroxide and staining with Alizarin Red S. A reduction in body weight minus uterine weight at term indicated that the two highest doses tested [125 and 250 mg TER/kg body weight orally] were maternally toxic. No increase in the ratio of resorptions/implantations was observed over the dose range tested. The highest dose of TER (250 mg/kg body weight) reduced the ratio of pregnant/treated female. A decrease in foetal body weight and an increase in foetal kidney weights were noted at 250 mg TER/kg body weight. Signs of delayed ossification (poorly ossified and not ossified bones as well as irregular spongy bones) and a higher incidence of minor skeletal malformations were observed at doses of 60 mg/kg body weight or more. These findings indicate that the no-observed-adverse-effect level for TER-induced embryofoetotoxicity can be set at 30 mg/kg body weight by the oral route.