Download PDF - The Pancreapedia

Figure 1. Comparative data on the age-related incidence of spontaneous tumors in female Syrian Golden
Hamster and MRC rats.
toxicological studies to avoid some serious
political and economical problems that may
surface. The unsettling problems with saccharin
studies present one of the known examples. In
this context, it must be emphasized that the
spectrum of spontaneous disease of any species
can vary from time to time and inclusion of a
similar number, or better a larger number of
control animals in each toxicological test, is
essential for unbiased results. A detailed
recommendation on the use of laboratory animals
in toxicological testing was published in 1979 84 .
Further comparative studies in other laboratory
animals emphasized the advantage of SGH in
toxicological studies. A comparative study of
aging MRC rats revealed that their survival was
about 20 weeks longer but their tumor incidence
was twice as high as in SGH. More female rats
developed tumors than male rats, especially of
the malignant variety, of which incidence was
twice as high as in the male rats. The tumor
frequency in female vs. male hamsters was 25%
vs. 26% compared to 64% vs. 39% in rats 85 .
Malignant tumors occurred in SGH in15% of
females and in 8% of males compared to 39%
and 8% in female and male rats, respectively.
This comparative study also revealed an
8
interesting phenomenon. By superimposing the
graphic curve relative to tumor incidence by age,
data in hamsters and rats overlapped when the
curve for rats moved to the right (toward the older
age position). When the first one-half-year of the
survival curve of rats is cut, the survival and tumor
curves of SGH and rats become identical (Fig. 1).
In that position, it appeared that rats at 70 weeks
of age show the same tumor rate, as do hamsters
at 30 weeks of age. In both species, tumor
incidence increased by age exponentially. After
reaching the so-called “tumor prone” age, the age
when tumors start developing (between 20-29
weeks in SGH and 60-69 weeks in rats), about
three times more rats develop tumors than
hamsters. Interestingly, the data on cumulative
number of tumors in both species showed similar
patterns. Both graphs exhibited a similar course
for 40-week-old hamsters and 80-week-old rats (a
difference of 40 week). Also, tumors in rats
developed explosively ( i.e., a ratio of 1:6 existed
for tumors in hamsters: rats (one tumor in hamster
compared to six tumors in rats at each point) 85 ).
The results indicated a fundamental difference
between hamsters and rats with regard to the
spontaneous lesions, which apparently was not
mediated simply by the longer survival, but rather