Effects of prolactin and growth hormone on DNA synthesis of rat mammary carcinomas in vitro.

Explants derived from mammary carcinomas of DMBA-treated female Sprague-Dawley rats were cultured for 5 days in Medium 199 containing insulin and corticosterone. The addition of ovine prolactin to the culture media resulted in a consistent significant increase in H3-thymidine incorporation into DNA. DNA synthesis of explants treated with either ovine or human growth hormone was intermediary to prolactin-treated cultures and control cultures. A combination of prolactin and human growth hormone often increased DNA synthesis above either hormone alone, suggesting a possible growth synergism between these peptides.