Paul Bastiani

Intralysosomal hydrolysis of thyroglobulin: specific and cAMP-mediated activation by TSH

Pig thyroid slices, pre-labelled with [125I]iodide, were incubated with or without thyrotropin (TSH), dibutyryl cyclic AMP (dbcAMP) or forskolin. After lysosome isolation, intralysosomal thyroglobulin (Tg) hydrolysis was determined by the increment in trichloroacetic acid (TCA)-soluble radioactivity. TSH stimulated the intralysosomal Tg hydrolysis. This stimulation was time and concentration dependent and was mimicked by forskolin or dbcAMP. When endocytosis and protein synthesis were blocked by inhibitors (nocodazole and puromycin) the stimulatory effect was still maintained. We conclude that TSH increases quickly and specifically, via a cAMP-mediated process, intralysosomal Tg hydrolysis, independent of its effects on endocytosis of Tg and lysosomal protease synthesis.

THE FOLLICULAR IODIDE POOL AS A TWO-COMPARTMENT SYSTEM : EVIDENCE FROM THE UNSTIMULATED THYROID GLAND.

The isotopic equilibrium method was used for a 60-day period to follow iodine turnover in control and hypophysectomized rats. After the suppression of TSH by hypophysectomy, only the captured iodide is used for iodination of thyroglobulin, the iodide recycling being abolished. In unstimulated gland, two metabolically distinct iodide compartments do exist which differ either in their chemical form or in their morphological distribution, or both.