Vaginal sensitivity to estrogen as related to mammary tumor incidence in mice.

The demonstration of the importance of ovarian secretion or exogenous estrogen to a high mam mary tumor incidence in mice was followed by numerous studies of the estrous cycles of mice of different strains, in an attempt to correlate high mammary tumor incidence with some peculiarity of the cycle. In general, no significant and consist ent correlation could be demonstrated in this regard. Korteweg and co-workers, however, fo cused attention on the possibility that, whereas outward manifestations of the cycle might be rela tively constant, fundamental differences may exist in the sensitivity of the genital tissues to estrogen, and that such differences may be related to the mammary tumor incidence. Van Gulik and Korte weg (5) reported that of one high tumor and two low tumor inbred strains, compared with regard to vaginal estrogen-sensitivity, the high tumor dba strain was the most resistant to exogenous estrogen stimulus, requiring roughly 3 times the amount of estrogen needed by the low tumor €¿ 57 strain for a comparable degree of vaginal stimulation. They pointed out also that Bonser (1) observed a some what higher percentage of positive vaginal smears in a low mammary tumor strain than in a high mammary tumor strain when both were injected with equal but varying doses of estrogen. On the basis of such findings, they theorized that, since a normal estrous cycle is essential for continued ex istence, those strains of low vaginal estrogen-sen sitivity probably produce larger amounts of estro gen and that this may be causally related to a high mammary tumor incidence. They reported also that reciprocal hybrids between the dba and C.57 strains showed an almost equal vaginal sensitivity to estrogen, intermediate between that of the pa rental strains, indicating that vaginal susceptibility