Prolactin administration stimulates rat hepatic DNA synthesis

Prolactin is an important growth modulatory hormone in fetal and adult tissues. Its administration stimulates enzymatic markers of the G₁ phase of cell cycle in rat liver and other tissues. To determine the effects of prolactin administration on hepatic DNA synthesis (S phase), rats received prolactin at 12 hour intervals for 48 hours and DNA synthesis was assessed by [³h]-thymidine incorporation. Prolactin administration stimulated DNA synthesis 2-4 fold above controls in the livers of adult and weanling animals. Increased incorporation of radiolabel was associated with the nucleus of hepatoparenchymal cells. These data support the hypothesis that prolactin may be a physiological regulator of hepatic DNA synthesis. Further, since stress stimulates prolactin secretion, we suggest that prolactin may participate in the hepatic compensatory hyperplasia elicited by the stress associated with partial hepatectomy.