Organic anion antiporter with apparent broad substrate specificity. Recognizes various substrates including thyroid hormones 3,3',5-triiodo-L-thyronine (T3), L-thyroxine (T4) and 3,3',5'-triiodo- L-thyronine (rT3), conjugated steroids such as estrone 3-sulfate and estradiol 17-beta glucuronide, bile acids such as taurocholate and prostanoids such as prostaglandin E2, likely operating in a tissue- specific manner (PubMed:10873595, PubMed:19129463, PubMed:30343886). May be involved in uptake of metabolites from the circulation into organs such as kidney, liver or placenta. Possibly drives the selective transport of thyroid hormones and estrogens coupled to an outward glutamate gradient across the microvillous membrane of the placenta (PubMed:30343886). The transport mechanism, its electrogenicity and potential tissue-specific counterions remain to be elucidated (Probable). {ECO:0000269|PubMed:10873595, ECO:0000269|PubMed:19129463, ECO:0000269|PubMed:30343886, ECO:0000305}. This is the function of SLCO4A1 (solute carrier organic anion transporter family member 4A1, ENSG00000101187).