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Effects of 3-Methyl-4-Nitrophenol in Diesel Exhaust Particles on the Regulation of Testicular Function in Immature Male Rats

CHUNMEI LI^*,

SHINJI TANEDA

AKIRA K. SUZUKI

CHIE FURUTA^*,

GEN WATANABE^*,

KAZUYOSHI TAYA^*,

From the ^* Department of Basic Veterinary Science, United Graduate School of Veterinary Sciences, Gifu University, Gifu, Japan; the Laboratory of Veterinary Physiology, Department of Veterinary Medicine, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan; and the Environmental Nanotoxicology Section, Research Center for Environmental Risk, National Institute for Environmental Studies, Ibaraki, Japan.

Correspondence to: Akira K. Suzuki, Environmental Nanotoxicology Section, Research Center for Environmental Risk, National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan (e-mail: suzukiak{at}nies.go.jp).

We investigated the effects of 3-methyl-4-nitrophenol (4-nitro-m-cresol, PNMC) isolated from diesel exhaust particles (DEP) on the reproductive functions of male rats. Twenty-eight-day-old rats were injected subcutaneously with PNMC (1, 10, or 100 mg/kg) daily for 5 days. The weights of the epididymis, seminal vesicle, and Cowper gland were significantly decreased in rats treated with 10 mg/kg PNMC. The plasma concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were significantly increased by PNMC at 100 mg/kg. However, the plasma concentrations of testosterone and immunoreactive (ir)-inhibin were significantly decreased by PNMC at 100 mg/kg. The testosterone content of the testicles was significantly decreased in the group treated with 100 mg/kg PNMC compared with the control group. Furthermore, testicular concentration of ir-inhibin was significantly decreased by PNMC at 1 mg/kg or 100 mg/kg. To investigate the direct effects of PNMC on the secretion of LH and FSH from the anterior pituitary gland, and on the secretion of testosterone from the testes, we exposed cultured anterior pituitary and interstitial Leydig cells to PNMC (10^–6, 10^–5, 10^–4 M) with or without gonadotropin-releasing hormone (GnRH; 10 nM) (for the LH and FSH tests) and human chorionic gonadotropin (hCG; 0.1 IU/mL) (for the testosterone test) for 24 hours. PNMC did not change either the basal or GnRH-stimulated levels of FSH and LH secretion. However, PNMC significantly inhibited both basal and hCG-stimulated testosterone production. These findings suggest that PNMC has a direct effect on the testes of immature male rats, causing a reduction in testosterone secretion.

     Key words: Leydig cells, nitrophenol, pituitary, testes

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