THE UNIVERSITY OF MANITOBA STUDIES ON OVINE PLACINTAL ...

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iniection of l25I-opl. t25t-opt (approximate'ly 2.5 x .l07cpm/10 ml
was injected intravenously lnto the left jugular vein and heparinïzed
bìood samples ( 5 n] ) were collected at frequent intervals from the
right jugular vein, Blood loss fron the circulation was compensated
for by the addition of 5 m] heparinized saline into the jugular
veln before each sampling. After co'l ìection, the blood samples were
immediately centrifuged at 3,000 rpm for 30 min at 4C and the
serum was malntained at 4 C until use,
Serum sample (one ml) was counted in the gamma
counter. Then two ml of l0% (Mvj ìce_co.ld triciìoroacetic acíd(TcA)
was added and the mixture was vlsorous.ly shaken. The preci -
pitate obtained after incubation at 4 C for I h was colìected by
centrifugation at 3,000 rpm for 30 min at 4 C, washed twice with
ice-çold TCA and counted .
For the determination of half-time disappearance rate
of l2sI-oPL ,' , the b'lood sampìes were
taken as described above at different intervals and the plot
of the logarithm of the radioactivity present in both the blood and
the TCA-insoluble materìal as function of time was obtalned. Two
half-times were calculated: tr(S) " which represents the ha.lf-time
calculated from the regress.ion line obtained by subtracting the
extrapolated values of the line of best fit over l0 to 25 mìn from
the values corresponding to the line drawn through the points up
to the first l0 min. The half-t.ime, t*(t- ) was ca'lculated di¡ect.ly
from theformula: 0.693/slope of tå(L). Similarly for tå(S):
0.693/slope of tå(s).