Actinomycin-insensitive Stimulation of Protein Synthesis in Rat Anterior Pituitary in Vitro by Dibutyryl Adenosine 3', 5'-Monophosphate

The effect of dibutyryl cyclic AMP (N6, O2'-dibutyryl cyclic adenosine 3', 5'-monophosphate) on protein synthesis and release has been studied in rat anterior pituitary gland. In unstimulated pituitary halves, incorporation of radioactive amino acids is maintained at a constant level for at least 5 hours. In response to dibutyryl cyclic AMP (5 mm), there is a 50 to 80% increase in the rate of incorporation into trichloracetic acid-insoluble proteins after 2 to 3 hours of incubation of male adenohypophyseal tissue. Concurrently, up to 30 min after addition of the cyclic nucleotide, there is a 275% stimulation of newly synthesized protein released into the medium, the effect being already maximal at 4 min. Actinomycin D, at a dose which inhibits RNA synthesis to less than 10% of the control rate, is without effect on the stimulatory action of dibutyryl cyclic AMP on either total protein synthesis or release. It is concluded that dibutyryl cyclic AMP stimulates both protein synthesis and release in the anterior pituitary gland, the effect on protein synthesis being probably exerted at the level of translation.