Thyroid hormone uptake in cultured rat anterior pituitary cells: effects of energy status and bilirubin

Transport of thyroxine (T-4) into the liver is inhibited in fasting and by bilirubin, a compound often accumulating in the serum of critically ill pat ients. We tested the effects of chronic and acute energy deprivation, bilir ubin and its precursor biliverdin on the 15-min uptake of [I-125]triiodothy ronine ([(1)25I]T-3) and [I-125]T-4 and on TSH release in rat anterior pitu itary cells maintained in primary culture for 3 days. When cells were cultu red and incubated in medium without glucose and glutamine to induce chronic energy deprivation, the ATP content was reduced by 45% (P < 0.05) and [I-1 25]T-3 uptake by 13% (NS), but TSH release was unaltered. Preincubation (30 min) and incubation (15 min) with 10 mu M oligomycin reduced ATP content b y 51% (P < 0.05) and 53% (P < 0.05) under energy-rich and energy-poor cultu re conditions respectively; [125I]T-3 uptake was reduced by 66% (P < 0.05) and 64% (P < 0.05). Neither bilirubin nor biliverdin (both 1-200 mu M) affe cted uptake of [I-125]T-3 Or [I-125]T-4. Bilirubin (1-50 mu M) did not alte r basal or TRH-induced TSH release. In conclusion, the absence of inhibitor y effects of chronic energy deprivation and bilirubin on thyroid hormone up take by pituitary cells supports the view that the transport is regulated d ifferently than that in the liver.