The cAMP synthesis by fetal rat thyroids is stimulated in vitro by thyrotropin (TSH) or forskolin during the 5 last days of intrauterine life. The effects are TSH- or forskolin-dose-dependent with equal responses to 20 mlU·ml––1 TSH or to 1 μM forskolin. The magnitude of the responses to TSH or to forskolin decreases significantly as the fetus is ageing. Since forskolin effects bypass hormone receptors, the adenylate cyclase activity can be concluded to decrease during the end of gestation probably in relation with thyroid iodine accumulation. The responses to TSH and forskolin becoming synergic between 19½ and 21½ days indicate modifications of adenylate cyclase properties probably related to some maturation of the enzyme.

Keywords:
Fetal rat thyroid, Adenosine 3′:5′-cyclic phosphate, Thyrotropic hormone, Forskolin
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© 1988 S. Karger AG, Basel
1988
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