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 nucleotide blocked T4 -induced shrinkage or tail pieces. Histological study of the segments after 4-days 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.