37
to years:
tive ab-!
other data and relates well to Marshall’s power func-
Dog
Age
A22B
576
A22C
A221
8m
4 yr
9 yr
9.5 vr
Measured plasma
fraction of
injected dose
&, of injected
dose/mi plasma
concentration,
—
in days. The coefficient
ecording » obtained by extending the straight line which fits the
after ininterval between 2 and 14 days to the day 1 intercept.
Measured
retention,
wie
er:
tion model."
| WAS @S-}
In Table 12 the measured retention and plasma
eposited
clearance are expressed as power functions where ¢ is
s still in
of the retention function was
TABLE 12.. PuasmMa RETENTION AND CLEARANCE OF Ba
place is,
The experimental slopes (the 6 term in the power funchus ob-!
tion R: = at—°) were measured from the data shown
spectra,
the dog
in Figure 32.
It should be noted that “crossover,” the time at
whieh the specific activity of the blood drops below
3Ba in- that of the skeleton, occurred between 14 and 100 days.
| power
tion vs,
An average slope has been drawn for the plasma and
retention eurves shown in Figure 32 to indicate a
coordi- ! “crossover” point.
S,
The feeal and urinary excretion rates, summarized
rtion of ; in Table 10, indicate a general decrease in the urimary
in the excretion rate with time after injection, whereas the
; shows
fecal excretion rate may have a peak somewhere beof the tween 2 and 4 days. The peak in the fecal excretion
ce i — ome
r
rate could be due entirely or in part to a fecal delay.
na conTable 11 tabulates the *Ba concentrations, as peron the
cent of injected dose per gram of ash, of various bones
ywever,
and segments of bones. It is probably not meaningful
re dur. ! to compare the actual quantity of 1**Ba retained in the
val be- * dogs because of their different ages, since Decker, et
d 576) | al’) have shown a marked difference in retention
i con-
Ire pe-
s after |
tivity
shape
ical of ;
from
r)
with age. However, the specific activity, in terms of
pereent of injected dose per gram of ashed bone seg-
incnt relative to the specific activity of the whole bone,
1.30 0-3
1.00 932
0.98 {9-59
0.829-97
2 1.76 %K
| 5.15 x
4.61 <
| 3.13 &
1073
103
1073
1073
6477
£148
(71-47
1-8
cal bone. One, therefore, expects that trabecular bone
would eventually lose activity more rapidly than cortical bone so that the ratio of the specific activity of
trabecular segments to that of a whole bone should
decrease with time after injection. A slight decrease is
shown by 1508 and 3113 days, but the effect is surprisingly small.
Thus, the analysis of tracer content in segments of
various bones suggests that, while changes are occurring, these changes are not rapid. Even four and nine
years after the isotope administration those bones or
portions of bone usually considered to turn over rapidly
still contain relatively high specific activity levels when
they are compared to the regions of compact cortical
bone where the turnover is known to be low.
SUMMARY
The whole-body retention, plasma clearance, and
bone deposition of **Ba have been measured in beagle
dogs. The '*Ba retention by these animals is clearly
relative 3Ba retention of bone segments and whole
not well described by a single power function, but does
relate well to Marshall’s theory of alkaline earth metabolism. No attempt has been madeto fit these data
with a series of exponential functions.
gram of ash in the bone segment than in the bone as a
whole. A ratio less than one indicates the opposite. At
eeven days after injection the trabecular bone of the
proximal and distal epiphyses has a specific activity
two or three times that of the cortical bone of the midshaft. This suggests a reactivity or turnover rate of
trabecular bone that is two to three times that of corti-
calcium blood curves. This steep slope is typical of all
barium, radium and strontium data that we have examined, but we have yet to appreeiate its significance.
The excretion rates showa general decrease with time
after injection.
The analysis of the tracer content in various bones
and segments of bones suggests that, even several years
is probably a significant quantity to compare between
the animals. Thus, in Table 18, we have compared the
hones at short times and long times after injection. A
ratio greater than one indicates more activity per
TABLE 13.
The plasma clearance studies indicate a steep slope
of the barium blood curve when compared to normal
Ratio ofr Specteic Activities OF Femur SEGMENTS TO SpPEctFic ACTIVITY OF ENTIRE FEMUR
Dog 576
Dog A22B
Proximal epiphysis
1.15
—
Proximal shaft
Proximal epiphysis plus shaft
Mid-shaft
Vist al shaft
0.706
0.998
0.523
0.734
—
1.24
0.90
—
ldistal shaft plus epiphysis
1.117
0.95
1.11
1.19
Femurbone segment
Distal epiphysis
Si
1508 day
1.31
3113 day
—
Dog 156
Dog A22C
Dog A22D
1.31
1.32
1.16
1.26
1.10
0.63
1.04
0.61
0.57
0.99
1.09
0.47
0.88
1.17
1.17
0.50
1.15
0.93
1.10
0.53
0.87
1.32
1.10
1.01
1.19
1.12
1.14
7 day
1.39
7 day
1.39
7 day
;
j
1.10
Avg. 7-day
value
1.29
Avg. 7 day/
1508 day
0.98
1.02