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Regular Article |
a Laboratory of Veterinary Physiology, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509, Japan
b Department of Pathology, Sasaki Institute, Tokyo 101-0062, Japan
c Air Pollutants Health Effects Research Team, Environmental Risk Assessment Project, National Institute of Environmental Studies, Ibaraki 305-0053, Japan
ABSTRACT
The present study investigated the effects of exposure of neonatal female rats to p-tert-octylphenol (OP) on estrogen-induced afternoon surges of LH, FSH, and prolactin (PRL) secretion, and on sexual behavior in adulthood. After birth, one group of female Wistar rat pups received s.c. injections of OP (100 mg/kg body weight [BW]; OP group) dissolved in DMSO, while the control group received DMSO only (DMSO group). In order to make a qualitative comparison, a third group was injected with estradiol-17ß (500 µg/kg BW; estradiol group) dissolved in DMSO. Injections were given on Days 1, 3, 5, 7, 9, 11, 13, and 15 of age. The rats from the OP and estradiol groups that were used for subsequent experiments were in persistent vaginal estrus. Spontaneous LH surge measured at Postnatal Days (PND) 78–81 was observed only in the DMSO group on the afternoon of the day of proestrus. At PND 115, randomly selected rats from each of three treatment groups were bilaterally ovariectomized (ovx), and 8 days later, Silastic capsules containing estradiol-17ß were implanted under the skin. Estrogen implants stimulated afternoon surges of LH, FSH, and PRL for two consecutive days in the DMSO group, but not in the OP and estradiol groups. Rats from the OP and DMSO groups underwent ovx at PND 186, and 6 days later they were treated with a combination of estradiol benzoate s.c. (15 µg/kg BW) and progesterone s.c. (2 mg/kg BW) to test the lordosis reflex. In response to this hormone treatment and mounting stimulus delivered by the stud male rats, the OP-treated rats were less receptive compared with control DMSO-treated rats, and thus the lordosis quotient and lordosis rating were significantly (P < 0.05) reduced in the OP group compared with the DMSO group. Analysis of the area of the sexually dimorphic nucleus of the preoptic area of the brain revealed that the area of this nucleus was larger in the OP group than it was in control DMSO rats. We conclude that the exposure of neonatal female rats to higher doses of OP disrupts the cyclic release of LH, FSH, and PRL, and interferes with the display of sexual receptive behavior in adulthood.
First decision: 24 October 2000.
1 Supported by a grant-in-aid from the Japan Society for the Promotion of Science.
2 Correspondence: Kazuyoshi Taya, Laboratory of Veterinary Physiology, Tokyo University of Agriculture and Technology, 3–5–8 Saiwai-cho, Fuchu, Tokyo 183–8509, Japan. FAX: 0081 42 367 5767; taya{at}cc.tuat.ac.jp
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