No abstract

Since the organic anion transporter-1 (OAT1) has been implicated in cortisol release from bovine and rat adrenal zona fasciculata cells, we addressed the question of whether OATs are present in human adrenal cortical cells. In the human adrenal cell line NCI-H295R, 24-h cortisol secretion increased up to 30-fold on exposure to forskolin. Incubation of forskolin-treated cells for 24 h with the OAT substrates probenecid, p-aminohippurate (PAH), glutarate or cimetidine inhibited cortisol release partly. RT-PCR did not reveal expression of human OAT1 and OAT2, but OAT3 and OAT4 mRNAs were detected in both NCI-H295R cells and human adrenal tissue. When human OAT3 (hOAT3) and hOAT4 were expressed in Xenopus laevis oocytes, only hOAT3 showed [3H]cortisol uptake in excess of that of water-injected control oocytes. Cortisol uptake via OAT3 was saturable with an apparent Kt of 2.4 microM. In NCI-H295R cells, [3H]estrone sulphate uptake was saturable, cis-inhibited by OAT substrates and trans-stimulated by preloading with glutarate or cortisol. Likewise, [3H]PAH uptake was cis-inhibited by estrone sulphate and trans-stimulated by preloading the cells with PAH, glutarate or cortisol, indicating functional expression of OATs in the plasma membrane of NCI-H295R cells.

Recently we provided evidence for the involvement of a probenecid-inhibitable anion exchanger in cortisol release from primary cultures of bovine adrenocortical cells. In the present study, we further characterized this exchange transporter. Adrenocorticotropic hormone stimulated ³H-p-aminohippurate (³H-PAH) uptake into as well as cortisol release from the cells about two- and tenfold, respectively. Probenecid inhibited both ³H-PAH uptake and cortisol release by about 55 and 63%. Preincubation of the cells with 1 mM PAH trans-stimulated ³H-PAH uptake by 30%, whereas cortisol release was inhibited by 30%. ³H-PAH uptake was cis-inhibited by 1 mM glutarate or by 1 mM cortisol in the medium, while cortisol release was trans-stimulated by glutarate. PAH in the incubation medium showed saturable cis-inhibition of ³H-PAH uptake. The release of cyclic adenosine monophosphate, a substrate of the renal PAH exchanger, was also inhibited by probenecid and trans-stimulated by glutarate. In summary, the trans-stimulation and cis-inhibition experiments support the concept of an anion exchanger involved in cortisol and cyclic adenosine monophosphate release from and PAH uptake into adrenocortical cells.

No abstract

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.