Action of Cyclic Adenosine 3',5'-Monophosphate in Vitro on the Uptake and Incorporation of Uridine into Ribonucleic Acid in Ovariectomized Rat Uterus

A system suitable for metabolic studies in vitro on uterine horns is described. Cyclic adenosine 3',5'-monophosphate (cyclic AMP) is effective at low concentrations (0.1 mm or 0.001 mm if used as the dibutyryl derivative) in stimulating the uptake by the tissue of uridine-5-3H and l-leucine-4,5-3H and their incorporation into RNA and proteins in ovariectomized rat uteri. The effect of cyclic AMP is rapid, and has a degree of specificity since other nucleotides like AMP and GMP do not induce parallel stimulation in the first 15 min of incubation. On prolonged exposure (2 hours), however, AMP and GMP cause effects similar to those of cyclic AMP, although their magnitude is smaller. The early effect of cyclic AMP appears to be a facilitated uptake of these metabolites. During the early phase (up to 15 to 30 min), there is no change in the relative specific radioactivity of RNA, the apparent rise in the labeling of RNA and proteins being due to the increase in the intracellular amount of radioactivity. On prolonged incubation (60 to 120 min), however, the relative specific activity increases, suggesting the activation of transcription processes. The rise in the synthesis of RNA in the early and late phases is not prevented by cycloheximide and does not appear to require the obligatory synthesis of protein or proteins.