INHIBITION OF THYROXINE-INDUCED RESORPTION OF TADPOLE TAIL BY ADENOSINE 3', 5'-CYCLIC MONOPHOSPHATE

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Abstract
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.