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Plant cytokinins are a group of growth promoting hormones with pronounced metabolic and regulatory effects not only on plants but also on microbial and animal cells (l). The effects of the N6-substituted derivatives of adenine, especially Zeatin (trans-6-(4-hydroxy-3-methylbut-2-enyl)- aminopurine) and Kinetin (6-furfurylaminopurine) on ultrastructure and on the in vitro response to Thyrotropin (TSH) or 8Br-cyclic AMP were studied in dog thyroid follicular cells.Thyroid slices were incubated in the presence of Zeatin or Kinetin with and without TSH or 8Br-cyclic AMP, after 30min. prior incubation in Earle's solution. Effects on ultrastructure were observed after 30min. to 6hrs. of incubation. The thyroid slices after removal from incubation flasks were fixed immediately in 3%glutaraldehyde-formalin in 0.05M phosphate buffer. Specimens were then treated as described elsewhere (2). Observations were performed with a Siemens IA electron microscope.

The acute ultrastructural effects of Thyroid Stimulating Hormone (TSH) in vivo or in vitro are well documented. However, little is known about chronic effects of TSH administration. The purpose of the present study was to define the ultrastructural changes induced by chronic TSH administration.Ten Mongrel dogs weighing between 18-20 kg were used in these studies. They were divided in two groups:Control group: (4 dogs) These dogs were administered saline solution, (0.09% NaCl) intramuscular for 10 days.TSH treated group: (6 dogs) These dogs received a daily intramuscular injection of TSH, 15 IU for 10 days.All dogs received 300 mg of Thyroid extract per day for 3 days prior to the operation. Then, they were thyroidectomized on the 11th day. Immediately after removal of the thyroid gland, tissues were fixed in glutaraldehyde 37, in phosphate buffer at pH 7.4 for 2 hrs.

The widespread contamination of the environment with PCB, a compound used extensively by industry in hydraulic and heat transfer fluids as well as plasticizers and solvents in adhesives and sealants, has resulted in detectable tissue levels in a large portion of the human population, domestic animals, and wildlife. Intoxication with PCB produces severe hepatic necrosis, degeneration of lymphoid tissues and kidney, skin lesions, decreased reproductive performance, reduced feed efficiency, and decreased weight gain. PCB also has been reported to reduce the binding of thyroid hormone to serum proteins and enhance the peripheral metabolism of thyroxine with increased excretion of thyroxine-glucuronide in the bile (Bastomsky, Endocrinology 95: 1150-1155, 1974).The objectives of this investigation were (1) to investigate the histopathologic, histochemical, and ultrastructural changes in thyroid FC produced by the acute (4 week) and chronic (12 week) administration of low (50 ppm) and high (500 ppm) doses of PCB to rats, (2) to correlate these alterations to changes in serum immunoreactive thyroxine concentration, and (3) to investigate the persistence of the effects of PCB on the thyroid gland.