Rapid effects of insulin on uridine metabolism in mammary gland explants

A study was made of the early actions of insulin on uridine metabolism in mammary glang explants. A stimulation of both labeled uridine uptake and its incorporation into RNA was demonstrated as early as 15 min after addition of insulin to medium bathing the tissue; these effects persisted for several hours. The metabolic fate of [3-H] uridine to UMP, UDP, and UTP was observed, whereas insulin had no effect on the quantity of 3-H present as uridine or uracil in these tissues. Further studies were performed in which insulin was also shown to have a rapid stimulatory effect on the incorporation of [32-P] phosphate into RNA; however, the uptake of the labeled phosphate was not affected by insulin. Experiments were also carried out to determine whether the effects of insulin on labeled uridine uptake require ongoing RNA and protein synthesis and whether uridine incorporation depends on concomitant protein synthesis. Incubation of explants with antibiotics which inhibit protein synthesis resulted in the complete suppression of the effects of insulin on labeled uridine uptake and its incorporation into RNA. In contrast, the effect of insulin on labeled uridine uptake does not appear to require ongoing RNA synthesis, since this effect persisted when RNA synthesis was significantly reduced by the presence of actinomycin D.