Effects of 5-Day Styrene Inhalation on Serum LH and Testosterone Levels and on Hypothalamic and Striatal Amino Acid Neurotransmitter Concentrations in Male Rats

Abstract

The volatile chemical styrene may impair male fertility. Testicular testosterone (T) production is controlled by the hypothalamic/pituitary/gonadal axis. From the mediobasal hypothalamus (MBH), gonadotropin-releasing hormone (GnRH) is released, which stimulates luteinizing hormone (LH) secretion from the pituitary, which in turn enhances T production. GnRH release is controlled by glutamate (GLU) and gamma-aminobutyric acid (GABA). GLU and GABA neurons are regulated by T. Thus, reduced fertility of styrene-exposed male workers may result from altered GLU/GABA neurotransmission, causing insufficient GnRH, LH, and T secretion. Therefore, we compared LH and T levels of male rats that have inhaled styrene (0, 150, 500, 1500 ppm for 6 h on 5 consecutive days) to GLU and GABA concentrations in the MBH and striatum. Animals were killed directly following the last exposure (immediate group) or after 24 h (recovery group). No suppression of LH or T levels was observed after styrene inhalation. LH levels of the immediate groups with 500 or 1500 ppm exposure were slightly but significantly elevated. Hypothalamic GLU and GABA concentrations remained unchanged. Increased striatal GABA concentrations were determined in recovery groups with 500 or 1500 ppm exposure. Striatal GLU concentrations remained unaffected. Thus, we demonstrate slightly increased LH and T levels in styrene-exposed male rats after inhalation of the two higher doses. This effect did not correlate with hypothalamic GLU and GABA concentrations. With the limitations inherent to any animal model, these data obtained from a 5-day exposure study with rats suggest, but do not unequivocally prove, that styrene may have also no reproductive toxicity effects in men chronically exposed to this chemical.