Effects of thyrotrophin stimulation for two hours on mouse thyroid cyclic AMP levels in vivo and in vitro

A thyrotrophin (TSH) stimulation in vivo in mice for 2 h, reflected by continuously increasing plasma triiodothyronine (T3) levels, was associated with an increase in the thyroid content of cyclic AMP (cAMP) during the first 25 min of stimulation; thereafter the level rapidly declined. A similar pattern of the cAMP response was found when mouse thyroid tissue was stimulated by TSH in vitro for 2 h. This is an in vivo demonstration of a type of cAMP response to prolonged hormonal stimulation that has been observed in several in vitro systems including thyroid tissue, generally referred to as hormone induced desensitization of adenyl cyclase. The present results indicate that the phenomenon is not confined to in vitro conditions but can be demonstrated also in vivo, and support the representativeness of in vitro experiments in this respect.