Uveal tissue respiration and glycolysis in
living experimental animals
Raymond Pilkerton, Peter H. Bulle, and J. O'Rourke
By application of data obtained for uveal blood flow by the nitrous oxide method in individual
experimental animals, reported in a previous paper, to oxygen and glucose determinations, the
oxygen consumption of uveal tissue was found to average 4.0 nl per gram per •minute and the
glucose averaged 0.047 mg. per gram per minute. These figures are compared with known
cerebral metabolic values. Data on COt obtained in this study support the concept that little
oxygen is utilized in the metabolism of the uveal tract.
A
respiration rate of 25 per minute. The expiratory
arm of the dog respirator was made as short as
possible to avoid CO2 accumulation. The infraorbital artery, anterior ciliary vein, and inferior
vena cava via the femoral vein were catheterized
with polyethylene tubing by the technique previously described.
Subsequent to the determination of uveal blood
flow in each animal, the animal was removed
from the 15 per cent N2O, 85 per cent O2 mixture
and ventilated on room air for 30 minutes. Blood
samples for pO2, pCO2, and pH studies were then
obtained from the infraorbital artery, anterior
ciliary vein, and lower inferior vena cava via the
femoral vein. Samples were collected into siliconized 25 c.c. Erlenmeyer flasks maintained in a
constant ice bath under mineral oil. After one
hour collection, the blood was anaerobically transferred to oiled, 10 c.c. glass syringes, and capped
with mercury. The pO2, pCO2, and pH were
determined by polarographic analysis with a modified Clark electrode for pO2 measurement and a
glass electrode for pCO2 and pH measurements.5
Blood for glucose determinations was obtained
from nonfasting animals prior to gas administration
for blood flow determination, and the glucose
determinations were made with the SomogyiNelson method for true blood sugar.9
In dogs, the average hemoglobin concentration
per 100 ml. blood was found to be 14.3 Gm.,30
which was used to calculate the average oxygen
capacity (14.3 x 1.34 = 19.16 volume per cent).
.lthough considerable work has been
done on the respiration of retinal tissue,1'8
until recently little information has become
available concerning the tissues of the
uveal tract.2'3 With data for uveal blood
flow as determined by the nitrous oxide
method reported from this laboratory,4 this
article concerns the measurement of oxygen
consumption, glucose metabolism, and carbon dioxide production of uveal tissue in
vivo.
Methods
In a previous report,4 male and female dogs of
approximately the same age, weighing between
16 to 22 kilograms, were anesthetized with pentobarbital sodium (35 mg. per kilogram), intravenously. The trachea was intubated with a cuffed
cannula, which was attached to an automatic
respirator with a tidal volume of 200 c.c. and a
From the Division of Ophthalmology, Department
of Surgery, Georgetown University Medical
Center, Washington, D. C.
This investigation was supported by Public Health
Grant No. NB 0233 from the National Institute
of Neurologic Diseases and Blindness, United
States Public Health Service, Bethesda, Md.
237
Downloaded From: http://iovs.arvojournals.org/ on 06/18/2017
238
Investigative Ophthalmology
April 1964
Pilkerton, Bulle, and O'Rourke
Table I. Oxygen values calculated as described for normal dogs breathing room
air for 30 minutes subsequent to discontinuation of nitrous oxide mixture
Average
Dog
Arterial
O2 tension ( p O : )
O 2 saturation ( % )
O2 content (vol. % )
86.7
97.5
18.68
108.9
100.0
19.16
72.0
95.0
18.20
110.0
100.0
19.16
104.0
100.0
19.16
106.5
100.0
19.16
97.9
98.7
18.92
Venous systemic
O2 tension
O2 saturation
O2 content
39.5
72.0
13.8
46.0
82.0
15.7
49.0
84.5
16.19
50.5
85.5
16.38
41.4
75.0
14.37
74.0
95.0
18.20
50.21
82.3
15.77
Venous anterior ciliary
O2 tension
O2 saturation
O2 content
69.9
94.0
18.01
65.9
93.5
17.91
67.0
94.5
18.10
80.1
96.0
18.39
86.0
97.5
18.69
82.0
97.0
18.59
75.01
95.42
18.28
A-V content difference (c.c. Ot/ml. blood)
0.013
0.007
Ocular blood flow
(c.c./Gm./min.)
0.55
0.56
Os consumption (microliters Ot/Gm./min.)
4.0
7.0
Blood oxygen dissociation curves for the dog were
used to determine oxygen saturation for the pO2
(mm. Hg). The product of the oxygen saturation
and the oxygen capacity is the oxygen content in
volume per cent. CO2 content in volume per cent
was obtained from a knowledge of pCO2 and pH
according to tables based on the HendersonHassalbach formula for the buffer systems in the
bicarbonate-carbonic acid system.11 Although
these formulas are for man, there is little practical
difference from those calculated for the dog.12
Results
Oxygen consumption. In Table I are the
data for calculation of oxygen consumption
as described for normal dogs breathing
room air for 30 minutes. The average O2
content of the arterial blood is 18.92 volume
per cent, that of the systemic venous blood
15.77 volume per cent, and that of the anterior ciliary vein draining the uvea 18.28
volume per cent. This gives an average A-V
content difference of 0.07 c.c. O2 per milliliter of blood. The average uveal blood flow
being 0.56 c.c. per gram per minute, the
average 02 consumption is 4.0 /d per gram
per minute.
Glucose utilization. The true blood glu-
Downloaded From: http://iovs.arvojournals.org/ on 06/18/2017
0.001
0.008
0.005
0.006
0.007
0.59
0.55
0.55
0.56
0.57
0.6
4.0
3.0
3.0
4.0
cose values obtained on nonfasting dogs
are presented in Table II. The average
arterial glucose concentration is 85 mg.
per cent, that of the anterior ciliary vein
77 mg. per cent, and that of the systemic
venous blood 74 mg. per cent. This produced an ocular A-V glucose difference of
0.08 mg. per cubic centimeter blood, and,
based on the uveal blood flow, gives an
average glucose utilization of 0.047 mg.
per gram per minute.
Carbon dioxide determinations. CO2
determinations calculated as previously described for normal dogs breathing room
air for 30 minutes are given in Table III.
The average CO2 content is 57.74 volume
per cent for the arterial blood, 58.50 volume
per cent for the systemic venous blood, and
55.76 volume per cent for the anterior
ciliary venous blood.
Discussion
The normal brain consumes O2 at an
average rate of 0.035 c.c. per gram per
minute,6 while the corresponding value
calculated for the uveal tissue is approxi-
Volume 3
Number 2
Uveal tissue respiration and glycolijsis 239
fasting, there is a range of arterial and
venous glucose values; however, this does
not affect the A-V differences with which
this article is concerned.
The possibility which was advanced0 to
explain the discrepancy of glucose and
oxygen uptake in cerebral tissues was that
the nonoxidized glucose represents a kind
of overflow of the initial anaerobic processes, producing an excess of lactate and
pyruvate, which would escape in the cerebral venous blood. This is of interest as it
is known that in addition to the high
glycolytic activity of the retina, it has a
unique capacity for splitting glucose into
lactic acid in the absence of oxygen.s The
values for oxygen consumption obtained in
our work are not greatly at variance with
values recently reported by Cohan and
Cohan.3 In a completely independent study,
mately 0.004 c.c. per gram per minute. It
is well known that aerobic metabolism of
the brain must continue at its normal rate
in order to preserve mental functions, and
that this O2 uptake seems to be very close
to, if not identical to, the minimal value
compatible with normal cerebral function.
With glucose utilization, the uveal tissue
(0.047 mg. per gram per minute) and brain
(0.055 mg. per gram per minute) are closer.
This is more than could be accounted for
even if the entire ocular oxygen supply were
utilized in aerobic metabolism, and it is
well known that the respiratory quotient
of the retina is close to 1.0.8
The possibility cannot be excluded that
analytical errors of glucose determinations
could be of sufficient magnitude to explain
this discrepancy of glucose and oxygen
uptake. Because the animals were non-
Table II. True blood glucose values of nonfasting dogs collected for 30 minutes
prior to administration of nitrous oxide for determination of blood flow
Dog
Arterial (mg. %)
Venous systemic
Venous anterior ciliary
A-Vi difference
(mg./c.c. blood)
Glucose utilization
(mg./Gm./min.)
1
1
90
80
80
0.10
0.055
3
2
85
75
75
0.10
1
4
70
60
60
0.10
90
80
80
0.10
0.059
0.056
5
90
80
0.05
85
0.05
0.055
0.028
Average
85
74
77
6
85
0.08
0.047
0.028
A-V difference quantitated to glucose utilization by multiplying by individual animal blood flow determinations.
Table III. Carbon dioxide values calculated as described for normal dogs
breathing room air for 30 minutes subsequent to discontinuation of the nitrous
oxide mixture
Dog
Arterial
CO2 tension
PH
CO2 content
I
2
3
4
5
38.0
7.41
65.1
45.4
7.31
62.6
37.5
7.39
61.7
24.0
7.49
48.9
31.5
7.38
50.7
35.28
7.39
57.7
Venous systemic
CO2 tension
pH
CO : content
40.2
7.39
66.1
49.4
7.28
64.0
45.9
7.33
63.0
26.3
7.44
48.3
33.9
7.35
51.0
39.2
7.36
58.5
Venous anterior ciliary
CO2 tension
pH
CO2 content
33.9
7.42
59.4
46.5
7.30
62.8
39.2
7.38
63.0
22.7
7.46
43.4
33.4
7.35
50.3
35.2
7.38
55.8
Downloaded From: http://iovs.arvojournals.org/ on 06/18/2017
1 Average
240 Pilkerton, Bulle, and O'Rourke
they determined an ocular A-V oxygen
diflFerence of 0.09 c.c. per milliliter of
blood in experimental dogs, and, basing
their calculations on an average ocular
blood flow of 0.67 c.c. per gram per minute, with a different method, obtained an
average oxygen consumption of 5.0 JU.1 per
gram per minute. Some of the physiologic
implications have been discussed. The essential diflFerences between the techniques
of blood flow used in their article and the
nitrous oxide method are discussed in another article.4
Projected values obtained by Bedell and
associates,2 using the Warburg apparatus
on excised iris tissue, also indicate a low
oxygen consumption, but the absolute figures are somewhat higher. This indicates
that iris respiration exceeds the values for
mean uveal respiration studied in vivo.
This is of importance since throughout the
studies of tissue respiration as measured in
vivo, the possibility of A-V shunts altering
the true respiratory picture remains. Although anatomic shunts have not been seen,
functional shunts cannot be ruled out.3'7
Attention is directed to the values obtained for CO2. Several of the individual
studies indicate that venous drainage of
the uveal tissues under normal conditions
contains less CO2 than does its arterial
supply. Although this discrepancy is supported by the average values for the series
of experiments, it is not consistent in individual experiments. The statistical significance of the series depends upon more
experimental data. However, the very closeness of the ocular venous and arterial
blood CO2 values tends to support the
concept that uveal metabolism may be
largely anaerobic, or at least that very
little oxygen is utilized in its metabolism.
Recognizing the CO2 A-V diflFerence to
be very close, we attempted to stress the
system by preliminary administration of
acetazolamide in a few animals. This procedure resulted in a widened A-V diflFerence
Downloaded From: http://iovs.arvojournals.org/ on 06/18/2017
Investigative Ophthalmology
April 1964
caused by a consistent elevation of the
CO2 of the anterior ciliary venous blood.
The implications of this are the subject of
a separate study.
Grateful acknowledgment is made to Drs.
Martin Rubin, Lawrence Lilienfield, and Kenneth
Moser of Georgetown University Medical Center,
for their assistance in blood gas determinations,
and to Mr. James Robbins for technical assistance.
REFERENCES
1. Hickam, J. B., Frayser, R., and Ross, J. C :
A study of retinal venous blood oxygen
saturation in human subjects by photographic
means, Circulation, 27: 375, 1963.
2. Bedell, R. H. S., Bulle, P. H., and O'Rourke,
J.:
Triiodothyronine, hyperthermia, and
corticosteroid influences on the respiration
of isolated iris tissue, A. M. A. Arch. Ophth.
70: 391, 1963.
3. Cohan, B. E., and Cohan, S. B.: Flow and
oxygen saturation of blood in the anterior
ciliary vein of the dog eye, Am. J. Physiol.
205: 60, 1963.
4. Pilkerton, R., Bulle, P. H., and O'Rourke,
J.: Uveal blood flow determined by the
nitrous oxide method, INVEST. OPHTH. 3: 227,
1964.
5. Severinghaus, J. W., and Bradley, A. F.:
Electrodes for pO2 determinations, J. Appl.
Physiol. 13: 515, 1958.
6. Lassen, N. A.: Cerebral blood flow and oxygen consumption in man, Physiol. Rev. 39:
183, 1959.
7. Sullica, L.: Observations of uveal blood flow
pattern in excised arterially perfused rabbit
eyes, Am. J. Ophth. 54: 1057, 1962.
8. Adler, F. H.: Physiology of the eye, ed. 3,
St. Louis, 1959, The C. V. Mosby Company.
9. Hawk, P. B., Oser, B. L., and Summerson, W.
H.: Practical physiological chemistry, ed. 13,
New York, 1954, Blakiston Company.
10. Altaian, P. L., editor: Blood and other body
fluids, Fed. Proc. 253, 1961.
11. Rossier, P. H., Buhlman, A. A., and Weissinger, K.: Respiration: Physiologic principles
and their clinical application, edited and
translated by Luchsinger, P. C , and Moser,
K. M., St. Louis, 1960, The C. V. Mosby
Company.
12. Rohn, H., and Fenn, W. O.: A graphical
analysis of the respiratory gas exchange,
Washington, D. C , 1955, American Physiological Society, Chart VIII.