8.
The more recent report of Walburg
[W1]
is
essentially a critique of the
concept of non-specific life-shortening, at least at the low doses of practical interest.
Walburg came to the conclusion that life-shortening effects
after irradiation may principally or perhaps exclusively be explained by the
induction or acceleration of neoplastic diseases.
supported by Storer {S6!.
This conclusion was also
All authors recognized that at higher doses other
mechanisms of death would be prevailing.
B.
9.
METHODOLOGY
Life-shortening can only be assessed on the basis of death, an end-point
that can be defined rather precisely in time.
However, it is usually more
informative to know the reasons why an animal dies than to identify with
great prevision the time at which the event occurs.
To ascertain the cause
of death is often a difficult exercise and, in some cases, an impossible one
since death is often the result of a variety of causes all acting jointly.
This is particularly true as animals grow older [D1, A2, D2] because aging
animals of all species (but particularly of the long-lived ones) die with
multiple lesions, contrary to what happens early in life, where the cause of
death is more often related to a single pathological entity.
In old animals
the number of possible causes of death increases and the primary or precipitating cause is difficult to diagnose.
Also, most irradiated animals die
of diseases which are unrelated to radiation exposure and this complicates
the identification of the terminal pathological syndromes.
Thus, multiple
disease conditions, and interactions between diseases in the same animals
should be correlated with parameters such as age and dose to provide a
meaningful interpretation of the pathology at death.
10.
The first difficulty with much of the work reviewed, particularly with
the oldest contributions, is the lack of careful pathological observations on
the animals at death, let alone the refined multifactorial analysis mentioned
above.
Many experimental series are therefore difficult to interpret, since
the representation - as accurate as it maz be in time - of the life-span
shortening, marks the complexity of the biological end-points.
Another
difficulty lies with the fact that even when good pathology is available,
this is usually collected at death.
Under these conditions it is impossible