 we conducted experiments to determine whether diesel engine exhaust affects reproductive endocrine function in growing rats . 
 the rats were assigned to three groups : a group exposed to total diesel engine exhaust containing 5.63 mg / m3 particulate matter , 4.10 ppm nitrogen dioxide , and 8.10 ppm nitrogen oxide ; a group exposed to filtered exhaust without particulate matter ; and a group exposed to clean air . 
 dosing experiments were performed for 3 months beginning at birth ( 6 hr / day for 5 days / week ) . 
 serum levels of testosterone and estradiol were significantly higher in animals exposed to total diesel exhaust and filtered exhaust ( p < 0.05 for each group ) as compared to the controls . 
 follicle - stimulating hormone was significantly decreased in the two groups exposed to diesel exhaust as compared to the control group ( p < 0.05 ) . 
 luteinizing hormone was significantly decreased in the total exhaust - exposed group as compared to the control and filtered groups ( p < 0.05 ) . 
 although testis weight did not show any significant difference among the groups , sperm production and activity of testicular hyaluronidase were significantly reduced in both exhaust - exposed groups as compared to the control group . 
 histological examination showed decreased numbers of step 18 and 19 spermatids in stage vi , vii , and viii tubules in the testes of both diesel exhaust - exposed groups . 
 this study suggests that diesel exhaust stimulates hormonal secretion of the adrenal cortex , depresses gonadotropin - releasing - hormone , and inhibits spermatogenesis in rats . 
 because these effects were not inhibited by filtration , the gaseous phase of the exhaust appears to be more responsible than particulate matter for disrupting the endocrine system.imagesfigure 1figure 2figure 3figure 4figure 5 
Images