Effects of 5-day styrene inhalation on serum prolactin and dopamine levels and on hypothalamic and striatal catecholamine concentrations in male rats

In several studies a hypersecretion of the pituitary hormone prolactin (PRL) in styrene-exposed workers has been described. This should cause reproductive problems like oligomenorrhea, secondary amenorrhea and reduced fertility [Arfini et al. (1987) J Occup Med 29:826-830, Bergamaschi et al. (1996) Neurotoxicology 17:753-760, Mutti and Smargiassi (1998) Toxicol Ind Health 14:311-323]. Secretion of PRL is tonically inhibited by the catecholamine dopamine (DA), which is released from hypothalamic neurons. It has been suggested that the activity of the enzyme dopamine-beta-hydroxylase (DBH) in the serum is a peripheral marker of central dopaminergic function. A slight reduction of such enzymatic activity was observed in styrene-exposed workers, which was associated with hypersecretion of PRL. To further investigate the putative effects of styrene on PRL release, male rats were exposed to styrene vapors (645, 2150 and 6450 mg/m(3)) for 6 h/day on 5 consecutive days. Animals were killed either directly following the last exposure (immediate group) or after a recovery period of 24 h (recovery group). Serum PRL and DA levels were measured by radioimmunoassay. Concentrations of catecholamines and their metabolites in the striatum and mediobasal hypothalamus (MBH) were determined by high performance liquid chromatography with electrochemical detection. Neither in the immediate nor in the recovery group were any statistically significant changes of serum PRL levels observed. Likewise, concentrations of catecholamines and their metabolites in the striatum and MBH remained unaffected. We conclude from these data that styrene, even at very high concentrations, has no adverse effects on the neuroendocrine mechanisms regulating PRL release and DA levels in the brain. With the limitations inherent in any animal model, we suggest that our data indicate that styrene also has no adverse neuroendocrine effects in humans.