同一基礎集団より乳癌高発および低発を指標として選抜確立された2つの近交系, SHNおよびSLN系マウスについて

抄録

A basal stock of Swiss albino mice was selected to two ways for high and low mammary tumorigenesis and two new strains were established (SHN and SLN) [27, 34] . They have still been selected and maintained by the strict brother×sister mating. SHN and SLN are now at F37 and F31, respectively.
In this paper, the changes in mammary tumorigenesis in both strains until F30 and the strain-difference in several characteristics concerning mammary tumorigenesis were briefly reviewed.
Mammary tumor incidence was increased and onset age of tumors was decreased with the advance of generation in SHN breeders and they were almost constantly 100% and 6-7 months, respectively, after F11. The effects of selection were not so marked in SLN breeders; mammary tumor incidence was fluctuate largely around the mean value of P generation and increased considerably after F23. The onset age of tumors became about 1 month later than P generation on average (Fig. 1) .
SHN virgins showed mammary tumor incidence of more than 90% and the onset age of 8-9 months. The effect of selection in SLN females was marked in virgins and the incidence and the onset age were 10-20% and 14-18 months, respectively, in each generation (Fig. 2) .
While the life spans of breeders and virgins which died without mammary tumors were 8-14 months and 13-19 months, respectively, in both strains, the variations were so large in each generation.
All mammary tumors checked were diagnosed as adenocarcinoma and the number of tumors per mouse was significantly higher in SHN than in SLN. The tumors of both strains were hormone independent (Fig. 3) [21], and the growth potential of tumors was higher in SHN than in SLN when transplanted into female nude mice (Fig. 4) .
While 1 out of 39 (2.6%) mammary tumor bearing SHN mice had metastases to the lung, the ratio increased up to 23% (10/43) by elongation of survival time of animals by surgical removal of mammary tumors.
Both normal mammary growth (Fig. 6) and preneoplastic mammary hyperplastic alveolar nodule (HAN) formation (Fig. 7) were much more marked in SHN than in SLN.
SHN was superior to SLN in mammary sensitivity to prolactin and ovarian hormones, whereas no clear differences between strains were observed in plasma prolactin levels at different reproductive states (Fig. 8) [15, 27] or mammary gland prolactin receptor during lactation [15] .
The pattern of estrous cycles of SHN females was characteristic in having long continued diestrous phases (Fig. 9) [24] . Among several characteristics examined as the indices of reproductivity (Fig. 10), characteristics concerning lactational performance, litter growth and litter growth rate, became better with the advance of selection in SHN (Fig. 10-E, F, G, H) .
The mammary tumor appearance was much higher and earlier in (SHN×SLN) F1 virgins than in (SLN×SHN) F1 virgins (Fig. 11), indicating higher mammary tumor virus (MTV) activity in SHN than in SLN. MTV antigen was identified by immunodiff usion test in the milk of both SHN (100%) and SLN (83%) [2] . It was also found in prostates and seminal vesicles of males of both strains [36] .
The responses of normal spleen cells and that of fat pad to PHA were significantly lower and higher, respectively, in SHN than in SLN.