The In Vitro mammary gland response to mammotropic hormones in mice with different mammary tumorigenesis

Mammary gland DNA synthesis estimated by the in vitro incorporation of [³H]thymidine in response to mammotropic hormones was compared between high and low mammary tumor strains of virgin mice (SHN and SLN). In SHN, mammary gland DNA synthesis when cultured in the medium containing insulin (I), aldosterone (A), estradiol-17β (E), progesterone, prolactin (PRL) and growth hormone (GH) showed a peak on day 2 of culture and declined thereafter. Quite the opposite was the case in SLN mammary glands. There was little strain-difference in mammary gland DNA synthesis when cultured for 6 days in the medium containing complete hormone mixture. However, DNA synthesis of SHN mammary glands cultured in the medium deficient in PRL was less than one-third of the control, whereas that of SLN glands was two-thirds of the control. Moreover, mammary gland DNA synthesis was decreased significantly by deficiency in GH or E in SHN strain only. In both strains, mammary gland DNA synthesis declined with an increasing dose of PRL when cultured in the medium containing I, A and PRL, which was associated with an activated secretory function. However, the changes were much more marked in SHN than in SLN. The results have demonstrated the higher dependency of SHN mammary glands than SLN glands upon mammotropic hormones, especially PRL. They further indicate that mammary gland potential for both growth and function is well reflected by mammary gland sensitivity to PRL.