Characterization of the effects of dibutyl phthalate on growth and male reproduction in frogs and rabbits

Abstract

Dibutyl phthalate (DBP), used extensively in consumer and industrial products, is known to adversely affect development and reproduction in rodents. Because DBP could be potentially ubiquitous and that studies using amphibians or mammalian animal models that closely mimic events in human reproductive development (e.g., rabbits) have not been performed, we studied its effects on growth and male reproduction in Xenopus laevis and Dutch-Belted rabbits. Frogs were exposed from gastrulation to 12 wk of life to 0.1, 0.5, 1, 5, 10, or 15 ppm DBP in 0.01% DMSO and DMSO alone or FETAX solution only (controls). Cumulative mortality rates for FETAX solution, DMSO, 0.1, 0.5, 1, 5, 10, and 15 ppm DBP were 9, 6, 5, 6, 44, 30, 59, and 100% at 1 wk and 35, 32, 29, 38, 60, 76, 98% by 68 wk. The incidence of malformations was increased in 5, 10 and 15 ppm DBP groups. Metamorphosis, a thyroid-dependent event, was delayed in 1, 5, and 10 ppm DBP groups. Larynx, a secondary sexual organ required for mating calls, was regressed in 1 and 5 ppm DBP. Reflective of this change, the percentage of time producing the mating call and ampiexus response were decreased. Furthermore, deleterious changes in spermiogenesis and structure of excurrent ducts were observed. Rabbits were exposed orally to 0 or 400 mg DBP/kg/day during gestation (gestation days 15-29), adolescence (post-natal weeks 4-12), or after puberty (for 12 wk). Male reproductive function was compromised to varying degrees in all DBP-exposed groups. The most pronounced effects were in rabbits exposed in utero where severe malformations of reproductive tract and poor semen quality were observed. In all DBP exposures, incidence of morphologically normal sperm was decreased and occasional atypical germ cells resembling carcinoma in situ of the testis were observed. In adolescent exposure group, the hypothalamic-pituitary-gonadal axis was affected and thyroid hormone concentrations were elevated. Collectively, these results indicate that: DBP is detrimental to frogs at relatively low concentrations; DBP affects non-rodent mammals as well as rodents; young animals are more susceptible to DBP; and DBP-mediated toxicity may involve disruption of thyroid hormone-, as well as androgen-dependent cascades.