Effects of forskolin and triiodothyronine on cyclic AMP production in rat thymocytes.

The effects of forskolin, 3,5,3'-L-triiodothyronine, and isobutyl methylxanthine on the accumulation of cyclic AMP were studied in rat thymocytes in vitro. Forskolin was found to stimulate markedly the production of intracellular cAMP which was partially released from the cells into the medium. Isobutyl methylxanthine, an inhibitor of cAMP phosphodiesterase, markedly potentiated the effect of forskolin on intracellular cAMP concentration, while triiodothyronine was ineffective. However, triiodothyronine acted synergically with forskolin and/or isobutyl methylxanthine. It was confirmed that low forskolin concentrations modulate the effects of the hormone.