In this study, we investigated the time-course changes of
hormone levels and sperm numbers in male Sprague-Dawley (SD) rats after neonatal exposure to
3,3',4,4',5,5'-hexachlorobiphenyl (
PCB169). Neonatal rats were given (through oral gavages) doses of 0, 0.025, 0.25, or 0.5 mg/kg-day of
PCB169 in
corn oil from postnatal day 1 (PND1) to PND7. The rats were sacrificed at PND8, PND21, and PND90.
PCB169 exposure was confirmed by the marked induction of liver
CYP1A1 mRNA expression at these three time points. The testicular daily sperm production and the sperm counts of the epididymis cauda significantly decreased at PND90 compared to that of control. Although reductions in serum
thyroxine and
triiodothyronine levels occurred at all these three time points and at both PND21 and PND90, respectively, the
mRNA expression of testicular
thyroid hormone receptor α1 was suppressed significantly only at PND8. The serum and testicular
testosterone (T) levels declined markedly at PND90 compared to the controls, but there was no effect at PND21. The
mRNA expression of testicular
steroidogenic factor 1 was inhibited markedly at the three time points, whereas those of StAR, P450c17, P450scc, and 3β-HSD were suppressed significantly only at PND90 relative to the controls.
PCB169 treatment had no effects on pituitary
follicle-stimulating hormone and
luteinizing hormone levels and on their receptors' expression in the testes. These results indicate that neonatal exposure to
PCB169 damages
hormone levels and testicular function in the long-term, resulting in persistent
hypothyroidism and decreases in adult T levels and sperm counts.