Alterations in thyroxine metabolism produced by cutaneous application of microscope immersion oil: effects due to polychlorinated biphenyls.
A 30% solution of a polychlorinated biphenyl (PCB) mixture or a microscope immersion oil containing 34% PCB, when applied to the skin of rats, led to substantial increases in the biliary excretion of intravenously injected [125I]thyroxine (T4) in bile: plasma 125I ratios, in the biliary clearance rate of plasma [125I]T4, and in bile flow. Both PCB preparations also elevated liver weight, thyroid 125I uptake, and Sephadex uptake of [125I]triiodothyronine (T3), and depressed serum T4 concentrations; serum T3 levels were unaltered by the PCB solution or by the immersion oil containing PCB. PCB, either in mineral or immersion oil, reduced the free T4 index (serum T4 X fraction Sephadex T3 uptake), indicating a probable reduction in the concentration of free T4 in serum; the free T3 index, on the other hand, was elevated in PCB-treated rats. The same type of immersion oil, in which the PCB was replaced by a hydrogenated terphenyl, was without effect on any of the indices studied. Thus, the effects of microscope immersion oil on T4 metabolism were due to its PCB content. In thyroidectomized, T4-maintained rats, PCB in mineral oil again increased Sephadex uptake of [125I]T3, greatly reduced serum T4, and moderately reduced serum T3 levels; the free T4 index was substantially reduced and the free T3 index moderately lowered in treated animals. These data indicate that in PCB-treated rats both the peripheral conversion of T4 to T3 and thyroid T3 secretion were enhanced. The metabolic impact of thyroid hormone in PCB-treated animals was unchanged, as shown by normal activity of hepatic mitochondrial L-alpha-glycerophosphate dehydrogenase.
D000287:Administration, Topical; D000818:Animals; D001646:Bile / Q000378:metabolism; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D008297:Male; D008853:Microscopy / Q000295:instrumentation; D008930:Mitochondria, Liver / Q000201:enzymology; D009821:Oils / Q000494:pharmacology; D011078:Polychlorinated Biphenyls / Q000008:administration & dosage* / Q000494:pharmacology; D051381:Rats; D012869:Skin Absorption; D013965:Thyroidectomy; D013974:Thyroxine / Q000097:blood / Q000378:metabolism*; D014284:Triiodothyronine / Q000378:metabolism
D009821:Oils; D014284:Triiodothyronine; D011078:Polychlorinated Biphenyls; D005993:Glycerolphosphate Dehydrogenase; D013974:Thyroxine