Immediate effects of TSH on the cavian thyroid.

Which stage of hormone synthesis is stimulated as the immediate response of the thyroid to thyrotropin (thyroid stimulating hormone, TSH)? Is there specific binding of TSH to thyroid tissue? Experiments were done with thyroids taken from propylthiouracil-treated guinea pigs to attempt to answer these questions. Such thyroids take up radioiodide (after 35 min in vitro; 10% of the total added; after 24 hours in vivo: 20% of the amount given)and, being only partially blocked, can utilize this iodide for hormone synthesis. Following pre-incubation (30 sec with or without TSH), incubation in Geys medium/air, proteolysis of the tissue and/or extraction of the incubation medium, tha iodinated compounds were isolated. These compounds were separated by thin layer chromatography and were either quantitated by cutting and counting the plates, or located by spraying the plates with the ferricyanide-ferrichloride-arsenic acid (FFCA) reagent. For iodide, similar procedures were used, on the same plates. This in vitro preparation, using partially blocked thyroid tissue, can serve as a model to detect slight alterations in iodide metabolism of the thyroid. TSH appears to bind specifically to thyroid tissue (more of the 125 I added was taken up in vitro by thyroid than by a control tissue). Finally, since after a 30-sec pre-incubation with TSH (control, no TSH), the tissue contained more DIT, less T3 and since less of the 125I taken up appeared as iodide, hormone synthesis and secretion appear to be the earliest responses of thyroid tissue to stimulation by TSH.