[Daily cyclic changes in thyroid cAMP in chickens (Gallus domesticus)]

48 White Leghorn cockereles (age: 4 weeks) were examined for daily alterations of thyroidal and plasma cAMP-concentrations by means of a radioimmunoassay. In the morning and in the evening the thyroidal cAMP-concentration was elevated. This elevation was accompanied by a decrease of thyroid-weight. Alterations of blood cAMP-concentration were without recognizable effect on thyroid function. It is assumed that mediated by the effect of the second messenger more thyreoglobulin is released at these times.