RELEASE OF CYCLIC AMP FROM THYROID CELLS IN VITRO

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Abstract
Half lobes of mouse thyroid gland were incubated in vitro with TSH [thyrotropin]. They released cyclic[c]AMP into the medium in amounts depending on the TSH concentration. The release of cAMP was greatest during the 1st h of incubation and subsequently at a lower rate. With an incubation time of 45 min the medium cAMP levels were from 43.0 .+-. 11.9 pmol/mg tissue protein for controls to 296.5 .+-. 29.2 pmol/mg tissue protein with 5 mU[units] of TSH in the medium. The tissue cAMP level reached a maximum after 15-30 min of incubation with TSH, then gradually decreased towards control level during 4 h of incubation. With 25 min of incubation the tissue cAMP level was 28.5 .+-. 8.8 pmol/mg tissue protein for controls, compared to 194.3 .+-. 27.0 pmol/mg tissue protein with 5 mU TSH in the incubation medium. Thyroxine release was of the same order during the later part of the 4 h incubation period compared to the 1st part. The results illustrate the quantitative importance of cAMP release. In the later part of the incubation period, the cell content of cAMP was low while thyroxine release remained high.