THE EFFECT OF INSULIN AND RELAXIN UPON MITOSIS (INVITRO) IN MAMMARY TISSUE FROM PREGNANT AND LACTATING PIGS

The rate of cellular proliferation in the mammary glands of pigs during late gestation and lactation was assessed by measuring the incorporation of H-3-thymidine (T(I)) into the DNA of mammary gland explants in vitro. The T(I) showed a linear response over the first 9 hr in vitro, and was not affected by the addition of 500 ng insulin/ml medium. From day 100 to parturition the T(I) rose, reached a peak at 2 d after parturition and declined during lactation to the lowest levels seen at day 21 of lactation. The inclusion of 0-1000 ng relaxin/ml medium on T(I) at 24-72 hr in vitro had no effect in stimulating T(I) in mammary tissue explants taken from either pregnant or lactating pigs.