INTRODUCTION
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The artificial rumen and simulated abomasal and intestina
l fluids procedure
was developed and used in conjunction with ruminant
metabolism trials as an
in vitro screening device to evaluate radionuclide
binding materials for
their possible use as feed additives to reduce the
levels of radioactivity
in miik and meat (Barth and Bruckner, 1969a,b; Barth
et al., 1969).
The
radionuclides of interest were mainly radiostrontium
and radiocesium.
The
effects of these binding materials on the availabil
ity of essential minerals
were also studied.
At this Laboratory, this procedure has been used
to study
the solubility and factors affecting the availability
of purified forms,
field-released forms, and fallout forms of fodine-13
1 and other radionuclides.
The simulated abomasum was then converted to simulate the intestine.
The
duodenum was simulated by adjustment of the pH to 4 and then 5.
Simulated
duodenal fluid was held at each pH only long enough to remove samples.
The
early jejunum was simulated by the addition of bile, pancreatin, trypsin,
and erypsin, and adjustment of the pH to 6.
Incubation was allowed to
proceed for 2 hours. The lower small intestine was simulated by adjusting
the pH to 7.5, followed by a 2-hour incubation period.
A study by Barth and Mullen (1972) strongly indicated
a correlation between
tadionuclide solubility in the in uvttro Procedure discussed
in this paper
and radionuclide availability for absorption in ruminants.
The artificial
rumen and simulated abomasal and intestinal fluids
procedure can be used to
predict, with reasonable accuracy, the tissue retention
and secretion of
various chemical and physical forms of radionuclides deposited
on edible
vegetation.
However, the solubility determined in vitro, and either
the
tissue retention or secretion determined tn vivo, of a purified
form of
the radionuclide must be known.
The artificial rumen and simulated abomasal and intestina
l fluids procedure
is currently being used in the Nevada Applied Ecology
Group (NAEG) plutonium
Program to study the solubility and behavior of purified
and field forms of
transuranics in the ruminant digestive tract.
In the case of purified or
laboratory forms, information ts obtained concerning the
effects of ruminalgastrointestinal conditions such as pH of the medium,
enzymes, and bile.
The solubility of a purified form, in conjunction with metabolis
m trial
data, may be used to predict milk secretion and tissue retention
of a field
or fallout form.
Data concerning the effects of season, type of vegetation
, and grazing
conditions on the biological availability of selected transurani
cs present
are obtained from trials using field or fallout forms.
Studies utilizing
the artificial rumen and simulated abomasal and intestinal fluids
procedure
in the NAEG plutonium program are described and the applicati
on of the avatlable data is discussed in this paper.
BRIEF GENERAL PROCEDURE
Rumen juice was collected from a fistulated steer, added to a basal medium
containing nutrients and saturated with carbon dioxide; the pH was adjusted
to 6.5 with sodium carbonate.
Erlenmeyer digestion flasks were inoculated with the rumen juice preparation
and a radioactive tracer was added.
Incubation was allowed to proceed with
carbonation for about 24 hours at 39.5°C. The artificial rumen was converted
to simulated abomasal fluid by the addition of hydrochloric acid and pepsin,
and adjustment of the pH to 3. Abomasal incubation was allowed to proceed
for 3 hours.
Samples were removed from the digestion flasks during all phases of the
digestion period and centrifuged, and the supernatant fluid was collected
for the analyses of soluble transuranics.
This procedure is modified as necessary to meet the objectives of various
NAEG program studies. A more complete description of the general laboratory
procedure is given by Barth and Mullen (1972).
RESULTS AND DISCUSSION
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Since these studies are in progress, all interpretations are subject to reconsideration as additional data become available.
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Purified Plutonium Studies
In these trials the solubilities of plutonium-238 nitrate, plutonium-238
eitrate, and plutonium-238 dioxide were studied in an artificial rumen and
simulated abomasal and intestinal fluids procedure (Barth and Mullen, 1974).
The in vitro procedure used was similar to that described under the general
procedure.
When plutonium was administered as plutonium nitrate solution to rumen juice,
13.8% remained soluble shortly after administration (about 15 minutes), 10.1%
remained soluble following the artificial rumen incubation period, 15.3% following the abomasal period, and 30.1% and 32.7% when held at pH 4 and 5, respectively, in the duodenal phase.
The solubility increased to 60.1% following
the addition of bile and enzymes and adjustment of the pH to 6.
When plutonium was administered as plutonium citrate (citrate buffered
plutonium solution), 20.6% remained soluble shortly after administration,
while 9% remained soluble following the artificial rumen incubation period,
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