The Composition and Origin of the Allantoic Fluid
in the Rabbit
by j . w. T. D I C K E R S O N and R. A. MCCANCE 1
From the Medical Research Council Department of Experimental Medicine,
University of Cambridge
INTRODUCTION
& R O U T H (1957) have described the characteristics of the rabbit's
allantoic fluid and shown that this contained much less sodium chloride than
the foetal serum but considerably more potassium. Other properties such as the
concentration of urea in the allantoic fluid and its temporal relationship to the
mesonephros made them conclude that it was the produce of this organ. They
did not make any measurements of the total osmolar concentrations of the fluids
or sera. Owing to the kindness of these authors we have been able to make this
measurement before their work was sent to press, and to consider their results in
relation to those which we had already obtained in the pig and in man (McCance
& Widdowson, 1954). This short note embodies our results and conclusions.
DAVIES
MATERIAL AND METHODS
Fluids were obtained from two rabbits 20 days after copulation. The parent
animal was killed by a blow on the neck, and blood obtained for serum by heartpuncture. The uterus was removed from the body and transferred to a clean
dissecting dish. On removing the uterine wall, the foetus surrounded by its sacs
was exposed. Each fluid was obtained by puncturing the membrane and sucking
out the fluid with a Pasteur pipette. When each sac was empty it was carefully
dissected away in order to expose the succeeding one. The fluid was transferred
to tared tubes and the amount obtained determined by weighing. Complete collections of the same fluid were pooled for analysis. Fluids were preserved under
toluene.
Urea was determined by the method of Lee & Widdowson (1937); Cl by the
method of Sendroy (1937); Na and K in the Beckman flame photometer. Total
osmolar concentrations were obtained from the freezing-points which were determined by Hervey's (1955) procedure.
1
Authors' address: Department of Experimental Medicine, Cambridge, U.K.
[J. Embryol. exp. Morph. Vol. 5, Part 1, pp. 40-42, March 1957]
ALLANTOIC FLUID IN THE RABBIT
41
RESULTS
There was no difficulty in confirming the essential findings of Davies & Routh.
The opalescent appearance of the allantoic fluid was highly characteristic and
distinctive. The table sets out the quantitative results which have been obtained.
The concentrations of urea and potassium in the serum were lower than those
Composition of the foetal fluids and of the maternal serum of the rabbit
at 20 days' gestation
Utter
1
Fluid
Amniotic
Allantoic
Maternal serum
Average
volume per
foetus ml.
0-96
0-38
—
2
Amniotic
Allantoic
Exocoelomic
Uterine
Maternal serum
1-58
0-67
3-29
—
—
Total osmolar
Urea
Na
K
Cl
concentration
mg./lOO ml. m. eq.ll. m. eq.ll. m. eq.ll.
m. moll I.
307
144
4-98
115
430
59-8
430
304
108
80
41-3
—
333
—
112
366
39-5
37-2
—
32-5
144
90-5
152
121-5
138-6
6-7
33-2
6-2
220
—
110
72-1
105-2
—
107-6
312
306
312
310
328
in the allantoic fluid but the concentrations of sodium and chloride higher.
Mainly owing to the latter the osmolar concentrations of the allantoic fluid were
lower than that of the serum, but by no means so much lower as they have been
found to be in the pig (McCance & Dickerson, 1956). The difference, as in the
pig, was largely due to the relative concentrations of sodium and chloride in the
serum and in the fluids.
DISCUSSION
If the conclusions of Davies & Routh (1957) are correct, and there seems no
reason to doubt them, the allantoic fluid of the rabbit may be regarded as being
mainly, if not entirely, the product of the mesonephros. This gives a chance of
studying the function of this organ, and it would appear to separate a fluid which
is hypotonic, due mainly to the concentrations of sodium and chloride in it being
so much lower than they are in the serum. Present knowledge suggests that the
foetal kidneys of all mammals do something similar, but naturally to very
variable degrees. If this be so, some source for the 'free' water excreted by these
foetal kidneys must be found. Aspects of this problem and its implications were
discussed by McCance & Widdowson (1954), and in the light of their work on
the pig it was suggested that the 'free' water was derived from the activities of
the allantoic membranes and, later, the placenta itself. Further work is being
carried out to prove or disprove this hypothesis.
42
J. W. T. D I C K E R S O N A N D R. A. M c C A N C E
SUMMARY
1. The allantoic fluid of the rabbit at the 20th day of gestation has been found:
(a) to be opalescent; (b) to be hypotonic relative to the maternal serum; (c) to
contain higher concentrations of urea and potassium than the maternal serum;
and id) to contain lower concentrations of sodium and chloride.
2. The facts known about this fluid indicate that it may be very largely a
product of the foetal mesonephros.
REFERENCES
DAVIES, J., & ROUTH, J. I. (1957). Composition of the foetal fluids of the rabbit. /. Embryol. exp.
Morph. 5, 32-39.
HERVEY, G. R. (1955). A method for determining the freezing points of biological fluids. Analyst,
80, 949, 284-9.
LEE, M. H., & WIDDOWSON, E. M. (1937). The micro-determination of urea in blood and other
fluids. Biochem. J. 31, 2035-45.
MCCANCE, R. A., & DICKERSON, J. W. T. ((1957). The composition and origin of the foetal fluids
of the pig. / . Embryol. exp. Morph. 5, 43-50.
& WIDDOWSON, E. M. (1954). Water metabolism. Cold Spr. Harb. Symp. quant. Biol. 19,
155-60.
J. (1937). Microdetermination of chloride in biological fluids, with solid silver iodate.
II. Titrimetric analysis. J. biol. Chem. 120,405-17.
SENDROY,
(Manuscript received 11: iv: 56)