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Variability of Mammary Carcinogenesis Induction
in Female Sprague-Dawley and Wistar:Han Rats: the Effect of
Season and Age
P. KUBATKA, E. AHLERSOVÁ, I. AHLERS, B.
BOJKOVÁ, K. KALICKÁ, E. ADÁMEKOVÁ, M. MARKOVÁ, M. CHAMILOVÁ, M.
ČERMÁKOVÁ
Institute of Animal Physiology, Faculty of Science, Šafárik
University, Košice, Slovak Republic
Received March 15, 2001
Accepted April 8, 2002
Summary
It is important to determine and clarify the variability of
mammary carcinogenesis induction in animal experimental studies
particularly in connection with chemoprevention projects. The
circannual seasonal rhythms of hormone levels or various
parameters within the immune system may involve factors
participating in mammary gland carcinogenesis. In our study, 19
experiments were conducted and all of them lasted for about 25
weeks after chemical carcinogen administration (DMBA or NMU)
under standard laboratory conditions. Females of two rat strains
- a medium susceptible Sprague-Dawley strain and a very low
susceptible Wistar:Han were used. We observed not only the
effect of seasonal changes but also the effect of age after
single or repeated carcinogen administration. The seasonal
dependence of mammary carcinogenesis with higher tumor incidence
during long days in comparison with winter short days has been
demonstrated in Sprague-Dawley rats. In experiments on the
Wistar:Han strain, certain features of seasonal character were
recorded, although the very low susceptibility of this strain to
mammary carcinogenesis might have influenced the results. A
limited period of carcinogen administration in early puberty
around postnatal days 43-46 (higher susceptibility), when
compared to the period after postnatal day 50, is the factor
significantly increasing incidence and frequency of mammary
carcinogenesis in the Sprague-Dawley strain. Our results
indicate the need to consider the effect of season and age of
animals at the time of carcinogen administration on rat mammary
carcinogenesis induction. However, the application of the
results obtained in one strain of experimental animals may only
lead to misleading conclusions.
Key
words
Mammary carcinogenesis · Seasons · Critical periods · Rat
strains · Susceptibility
Reprint
requests
Prof. I. Ahlers, M.D., D.Sc., Institute of Animal Physiology,
Faculty of Science, P.J.Šafárik University, Moyzesova 11, 041 67
Košice, Slovak Republic. fax: +421-55-6222124. e-mail:
iahlers@kosice.upjs.sk
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