Abstract |
- Two separate studies were conducted during this research
project. Oysters were irradiated with 500 and 1000 rads and 5, 10,
20, 50, 75, 100, 150, and 200 krads in the first study in order to
determine the effects of ionizing radiation on survival and growth
rates. Two periods of high mortality were noted; the first occurred
from 2 to 7 days postirradiation in oysters receiving 75 to 200 krads
and was associated with an "acute lethal tissue degenerative
syndrome." The second mortality period occurred from 40 to 60 days
postirradiation in oysters exposed to 10 krads or more and was caused
by a "lethal tissue degenerative syndrome." The LD-50 dose was
found to be a complex function of time from the moment of irradiation
until approximately 80 days postirradiation. The 238-day LD-50 value
was 16.5 krads.
The mean wet weight of oysters exposed to 20 krads was
significantly less than that of the controls from 167 to 238 days
postirradiation. Analysis of the results suggest a dose dependent
wet-weight relationship in the 5 and 10-krad oysters; they did not
weigh significantly less than the controls. Although not
statistically significant, the mean wet weights of oysters exposed
to 500 and 1000 rads exceeded that of the controls from 43 to 238
days postirradiation.
In the second study, oysters were irradiated with 200 R,
600 R, 1000 R, 5 kR (X irradiation), and 8, 16, and 40 krads (gamma
irradiation). The purposes of the second study were to analyze
histopathologically, the degenerative syndromes and subsequent tissue
repair processes in the stomach, gut, collecting ducts, and digestive
tubules. Degenerative changes were seen only in the digestive
tubules of 5- and 8-kR oysters while in oysters exposed to 16 and 40
krads, degenerative changes coincided with the lethal tissue
degenerative syndrome noted in the survival-wet weight study. A
tissue regeneration sequence was observed in the stomach, gut,
collecting ducts, and digestive tubules of most oysters exposed to
16 krads and in a smaller number of oysters exposed to 40 krads.
Tissue regeneration was first observed in the digestive tubules and
subsequently in the stomach, gut, and collecting ducts. Repopulation
of the digestive tubules involved reepithelialization of the tubule
with large, undifferentiated crypt cells followed by their
differentiation into secretory and absorptive cells. Tissue recovery
in the stomach, gut, and collecting ducts was initiated by islands of
small basophilic cells not previously described in these tissues.
Rapid mitotic proliferation of these cells and their subsequent
differentiation into basal epithelial cells, resulted in the
reepithelialization and eventual recovery of these tissues.
|