Inhibition of thyroxine-induced resorption of tadpole tail by adenosine 3',5'-cyclic monophosphate

Small segments of tail of Bufo bufo japonicus tadpoles were cultured in medium containing thyroxine (T₄) and dibutyryl cyclic AMP (dbcAMP). Like prolactin, the cyclic nycleotide blocked T₄-induced shrinkage of tail pieces. Histological study of the segments after 4 days of culture revealed that dbcAMP suppressed degenerative changes induced by T₄. The inhibitory effect of prolactin on T₄-induced tail regression was promoted by caffeine an inhibitor of adenosine 3',5'-cyclic monophosphate (cyclic AMP)-phosphodiesterase. The effect of prolactin on the level of cyclic AMP in the tail was also studied in vivo. Sixty min after prolactin injection, the cyclic AMP level was 2-3 times the control value. Possible involvement of cyclic AMP in the action of prolactin, which blocks tail resorption induced by T₄, was discussed.