I. Ahlers et al., Very low sensitivity of Wistar : Han female rats to chemocarcinogens in mammary carcinogenesis induction, NEOPLASMA, 45(6), 1998, pp. 373-376
Recently a great variability of various mouse and rat strains in the sensit
ivity for mammary tumors induction by means of physical (ionizing radition)
or chemical (mostly 7, 12-dimethylbenz/a/anthracene, DMBA and N-methyl-N-n
itrosourea, NMU) initiating agents was noted. The categorization into four
groups was recommended in rats; the first group with high sensitivity (the
incidence of tumors practically 100%, the frequency of tumors per entire tr
eated group 2.0), the second with average type of sensitivity (incidence be
low 100%, frequency between 1.0-2.0), the third with low sensitivity (frequ
ency 0.3-0.4) and the fourth with zero sensitivity as the response to singl
e standard dose of DMBA.
After initial observations we decided to analyze the sensitivity to mammary
carcinogenesis in the female rats of Wistar: Han strain, used frequently i
n central European region. Twenty mg Of DMBA by gavage as single dose, or t
hree-times 10 mg by gavage as repeated consecutive doses in three-day inter
vals, or 30 mg/kg b.w. of NMU intraperitoneally were administered, always b
etween 50-55 postnatal days (single doses) or between 50-60 days (repeated
doses of DMBA). The average incidence of mammary tumors did not exceed 10%
and the entire group tumor frequency was about 0.1 for both carcinogens use
d. The data allowed us to indicate the female Wistar: Han rats as animals w
ith "very low" sensitivity for the initiation of mammary tumors by single d
ose of DMBA or NMU; being in this way very close to the insensitive strains
. The fact of "sensitivity" improvement to higher range after repeated dose
s of DMBA indicated a non-genetic background of the changed sensitivity.
Our results support the need to use more then one rat strain for initiation
of mammary carcinogenesis, and for assessing the bright range of the biolo
gical response. In this situation the concept of "multi-strain" assay seems
to be the optimal.