UNCLASSIFIED
The activity in the head was 13 percent of that in the G.I. tract at 0.5
hours after exposure. About 80 percent of the Sr in the head appears to
be associated with aerosol particles trapped in the naso-pharyngeal region. (This apparatus appears to have a high filtering efficiency in the
mouse.) The remainder (20 percent) of the Sr in the head is fixed in
the bonesof the skull.
Similar Sr85Cl2 dry particles were suspended in water and administered by stomach tube. The amount present in the G.I. tract at 0.5 hour
was used as the basis of comparison (Fig. 3B). The Sr in the respiratory tract was 0.6 percent of that found in the G.I. tract at this time. —
It is interesting to note {in terms of the G.I. tract activity at 0.5 hour)
that about half the amount of activity in the respiratory tract found after
inhalation was present after gavage. This indicates that approximately
half the material in the lung is derived from alveolar exchange with the
circulation.
The rate of clearance of material from the G.I. tract,
liver, and respiratory system was similar following inhalation exposure
and gavage (Fig. 3).
Following gavage, however, the activity in the head
and skeleton continued to increase for the first few days, and by the third
day this activity had reached 80 percent of the value observed following
the inhalation exposure. The activity in the liver after 2 hours was approximately the same following gavage or inhalation exposure. These
findings suggest that under the conditions of this experiment, a considerable fraction of the activity deposited in the skeletal tissue and liver
after inhalation may have been transported across the membranes of
the G.I. tract.
As a means of investigating further the role of G.I. absorption following an inhalation exposure, the oesophagi of a group of mice were
ligated and severed, and these mice along with a group of controls were
subjected to an inhalation exposure in the manner previously described.
Half of the control animals underwent a sham operation prior to exposure
to indicate the effects of the surgical operation itself on the animals.
At 20 hours following exposure, the amount of internally deposited Sr in
the skeleton and liver of the experimental animals was approximately
35 percent of that found in the controls (normal and sham-operated,
Table 1). The activity in the stomach and the small and large intestines
in the oesophagus -ligated animals gives an indication of the endogenous
excretion of absorbed activity. While the effect of closing off one portal
of entry appears to be that of lowering the internal deposition to approximately one-third, it must be borne in mind that the results here are
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