Sensitization of the Adrenal Cortex to Angiotensin II
in Sodium-Deplete Man
By Wolfgang Oelkers, Jehoida J. Brown, Robert Fraser, Anthony F. Lever,
James J. Morton, and J. Ian S. Robertson
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ABSTRACT
The effect of sodium depletion on the dose-response relationships of angiotensin II to
aldosterone and blood pressure was studied. Arterial plasma angiotensin II and
aldosterone and arterial blood pressure were measured before and during the incremental infusion of angiotensin II into sodium-replete and sodium-deplete subjects. Sodium
depletion caused a distinct steepening of the angiotensin H-aldosterone dose-response
curves in four of five subjects and a concurrent diminution in the pressor effect of
angiotensin II. Administration of angiotensin II did not demonstrably alter the half-life of
aldosterone. Sodium depletion did not change the plasma concentrations of sodium or
potassium, but it was accompanied by a significant increase in plasma levels of 11hydroxycorticosteroids and magnesium. The contrasting effects of sodium depletion on
the aldosterone and the pressor dose-response curves favored sodium retention. These
results are consistent with an important role for the renin-angiotensin system in the control of aldosterone secretion in man.
KEY WORDS
magnesium
aldosterone
ACTH
• The hypothesis formulated by Gross (1, 2) and
Davis (3) that the renin-angiotensin system is a
regulator of aldosterone secretion has been supported by studies in man which show that the infusion of angiotensin II stimulates increases in
aldosterone secretion (4), excretion (5, 6), and
plasma concentration (7). Plasma renin assays have
provided further support for this hypothesis,
because parallel changes in renin and aldosterone
have been demonstrated (8, 9) in a wide variety of
physiological and pathological situations, albeit
with some noteworthy exceptions. It should be
emphasized, however, that such evidence is circumstantial; the possibility that the changes in
renin and its active product, the octapeptide
angiotensin II, are within a range capable of affecting aldosterone secretion remains to be demonstrated (8, 10).
Two recent reports (11, 12) have seriously questioned the role of the renin-angiotensin system in
the control of aldosterone secretion during sodium
From the Medical Research Council Blood Pressure Unit,
Western Infirmary, Glasgow G i l 6NT, Scotland.
Dr. Oelkers' present address is Klinikum Steglitz der Freien
Universitat, Berlin.
A preliminary report of this investigation has been presented
(International Workshop Conference on Mechanisms of Hypertension, Los Angeles, Excerpta Medica, in press).
Received July 27, 1973. Accepted for publication October
10, 1973.
Circulation Research, Vol. XXXIV, January 1974
blood pressure
sodium
dose-response curves
potassium
deprivation in man. Mendelsohn et al. (12) could
not find a consistent increase in plasma angiotensin
II concentration or an increase in sensitivity of the
adrenal cortex to angiotensin II in sodium depletion. Boyd et al. (ll) similarly claimed that
adrenocortical sensitivity to angiotensin was not
markedly enhanced in sodium depletion. However,
their results differed from those of Mendelsohn et
al. (12) in that they observed fairly consistent,
albeit small, elevations in basal plasma angiotensin
II levels. Both groups concluded that the reninangiotensin system was not the major factor causing
the increased aldosterone secretion in sodiumdeplete man.
These two studies (11,12) are, however, open to
objections. Each attempted to assess adrenocortical sensitivity by the administration of angiotensin
II at a single dose rate in sodium repletion and
sodium depletion. As explained elsewhere (13), it is
not possible to distinguish changes in the threshold
response from changes in the slope of the doseresponse curve by examining the action of single
doses of angiotensin II. Therefore, the effects of a
series of graded doses must be assessed as conceded by Boyd et al. (11). Furthermore, Boyd et al.
(11) used venous blood to measure angiotensin II
during the intravenous administration of angiotensin. It has been shown (14) that, during the intravenous infusion of angiotensin II, the arterial
plasma concentration of angiotensin II immu69
70
OELKERS, BROWN, FRASER, LEVER, MORTON, ROBERTSON
noreactive material differs considerably from the
venous plasma concentration. Consequently, under
these circumstances, venous plasma cannot validly
be used to assess the concentration of angiotensin II
reaching the adrenals in arterial blood.
In the study presented in this paper, the problem of renin-angiotensin involvement in
aldosterone secretion induced by sodium depletion
in man has been reinvestigated. Angiotensinaldosterone relationships in other species have
been reviewed recently by others (15-17).
Methods
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All experimental procedures were approved by the
Ethical Supervisory Committee of the Western Infirmary, Glasgow. Informed consent was obtained from the
participants: one male convalescing from duodenal
ulceration, one female with mild lymphedema localized
to one foot, and seven healthy laboratory workers were
used. Their ages ranged from 26 to 40 years. The highest
arterial blood pressure attained in any subject during
the administration of angiotensin was 135/95 mm Hg.
Infusions of l-Asp-NH2-5-Val-angiotensin II (Hypertensin, Ciba) and of l-Asp-5-Ile-angiotensin II (Division
of Biological Standards, National Institute for Medical
Research, London) were given; l-Asp-5-Ile-angiotensin
II was purified by passage through 0.22-fj.m Millipore
filters.
Plasma angiotensin II concentration was measured by
the method of Dusterdieck and McElwee (18). Plasma
aldosterone was estimated by a modification of the double-isotope derivative technique of Fraser and James
(19) or by the radioimmunoassay method of Fraser et al.
(20). A close correlation has been demonstrated (20) in
concurrent measurements made in the same plasma samples with these two techniques. Plasma 11-hydroxycorticosteroids were estimated by the fluorometric method
of Mattingly (21); sodium and potassium concentrations in plasma and urine were estimated by flame
photometry, and plasma magnesium was estimated by
atomic absorption spectrophotometry (22).
Hlood pressure was measured by a sphygmomanometer; data for control and infusion periods were the
means of four to six measurements. Mean blood pressure
was calculated as the diastolic pressure plus one-third of
the pulse pressure.
Intravenous infusions and arterial and venous sampling were performed via indwelling catheters as
described previously (14). All experiments were started
between 8 AM and 9 AM after 8-12 hours of overnight
recumbency and fasting. The subjects lay quietly
throughout the studies in an isolated room, but they
were not permitted to sleep.
PRELIMINARY EXPERIMENTS
Establishment of Steady Plasma Concentrations of
Angiotensin II and Aldosterone during Angiotensin II
Infusion.—Two males received dextrose (5%, iv) for 60
minutes followed by l-Asp-NH2-5-Val-angiotensin II (6
ng/kg min"1) for 150 minutes. Venous blood samples
were taken at 20 minutes and 5 minutes before the administration of angiotensin and at 30, 60, 90, 120, and
PLASMA
ALDOSTERONE
ng / 100 ml
PLASMA
o
ANGIOTENSIN II
pg/ml
200
60
120
150 min.
FIGURE 1
First preliminary experiment showing changes in plasma
aldosterone concentration (top) and venous angiotensin II immunoreactive material (bottom) before and during an infusion
of angiotensin II (6 ng/kg min~') in two normal subjects.
150 minutes after the administration of angiotensin had
been started (Fig. 1).
Comparison of 5-Val- and 5-He-Angiotensin II.—
Two males were studied on two different occasions separated by an interval of 3-4 weeks. For 4 days they were
fed a fixed diet containing 147 and 152 mEq of sodium
and 60 and 71 mEq of potassium daily, respectively. On
the morning of the fifth day they received an infusion of
5% dextrose for 1 hour followed by the administration of
angiotensin, l-Asp-NH2-5-Val-angiotensin II, on the first
occasion and l-Asp-5-Ile-angiotensin II on the second
occasion, at incremental dose rates of 2 ng/kg min"1 and
4 ng/kg min"1 for 60 minutes each and 8 ng/kg min"1 for
15 minutes (limitation of infusion duration at the highest
dose rate was necessary because of a shortage of the 5Ile-octapeptide). Arterial and venous blood samples
were drawn at 20 minutes and 5 minutes before the administration of angiotensin and at 2-5 minutes before the
end of each angiotensin infusion period. Because of the
brief infusion, aldosterone was not measured at the highest dose rate.
Effect of Administration of Angiotensin on the Metabolic Clearance of Aldosterone. —In one normal male
3
H-labeled aldosterone (10 fie, iv) (40 c/mM, New England Nuclear Corp.) was injected, and 10 ml of blood
was withdrawn into heparin 1, 7, 12, 30, 50, and 70
minutes later from a vein in the opposite arm. 1-AspNH2-5-Val-angiotensin II was then infused (6 ng/kg
min"1); a second dose of labeled aldosterone was given
60 minutes after the start of the infusion, and venous
blood samples were subsequently withdrawn as before.
14
C-Aldosterone (900 dpm) was added to each
plasma sample, which was then extracted with ten
volumes of dichloromethane. The extract was washed
with one volume each of sodium hydroxide (0.1N), acetic
Circulation Research, VoL XXXIV, January 1974
71
ANQIOTENSIN II AND ALDOSTERONE
acid (O.IN), and water and was evaporated to dryness.
The residue was acetylated by incubation with acetic
anhydride (0.1 ml) and pyridine (0.1 ml) at 35°C for 16
hours and, after the removal of excess reagents, 100 fig
of aldosterone diacetate was added. The residue was
then chromatographed according to the thin layer
system and paper system no. 2 described by Fraser and
James (19). The aldosterone diacetate regions of the
paper chromatogram were eluted and assayed for 3H
and 14C. From these data the 3H-aldosterone concentration of the plasma samples and the half-life of the hormone were calculated.
MAIN EXPERIMENT
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This experiment was performed in four males and one
female. Each subject received a constant diet with a
sodium content of 129-150 mEq and a potassium content
of 55-84 mEq daily for 3 full days; the first angiotensin
infusion study was performed on the morning of the
fourth day. Following the infusion of angiotensin,
furosemide (30-60 mg, iv) was given, and each subject
was then changed to a daily diet containing only 9-12
mEq of sodium; potassium intake was maintained at the
previous level. On the morning after the third full day of
low-sodium intake the angiotensin infusion was repeated.
Each infusion study included the administration of
5% dextrose for 60 minutes, followed by the administration of l-Asp-NH2-5-Val-angiotensin II at 2, 4, and 8 ng/
kg min"1 for 60 minutes each. Arterial and venous blood
samples were withdrawn at 20 minutes and 5 minutes
before the beginning of infusion of angiotensin and 55
minutes after the beginning of each infusion. As previously reported (14), during the infusion of angiotensin
[I, arterial plasma concentrations of immunoreactive
naterial consistently exceeded venous plasma concentrations; the discrepancy increased with increasing
ioses. Consequently, only the arterial values were considered in the present paper.
In each infusion study, blood pressure was measured
3very 10 minutes beginning 40 minutes before the inroduction of angiotensin.
Results
PRELIMINARY EXPERIMENTS
Establishment of Steady State of Angiotensin II
ind Aldosterone.—As shown in Figure 1, during
hf infusion of angiotensin II at 6 ng/kg mirr1, there
vas no tendency for venous angiotensin II immuloreactive material to increase further after 30
ninutes or for aldosterone to change systematically
ifter 60 minutes. This effect on aldosterone conirms earlier reports (7, 11). Therefore, 60 minutes
rom the start of a given dose of exogenous
.ngiotensin was chosen as a suitable sampling time
or the estimation of plasma aldosterone.
Comparison of 5-Val- and 5-Ile-Angiotensin
I. —In two subjects and with both forms of
ngiotensin II, comparable increments in arterial
ilasma angiotensin II produced comparable increIrcuUtton Remrch, Vol XXXIV. January 1974
AM BP
mm Hg
PLASMA
ALDOSTERONE
ng/ 100ml >i
3
100
10
PLASMA ANGIOTENSIN II
1000
pg/ml
FIGURE 2
Second preliminary experiment showing changes in mean blood
pressure (AMBP) (top) and plasma aldosterone concentration
(bottom) in relation to arterial plasma angiotensin U (abscissa)
before and during infusion of angiotensin II at 2, 4, and 8 ng/kg
min~i in two normal subjects (open and solid circles). The two
lowest points with each Infusion indicate basal samples taken
during dextrose infusion; incremental points were recorded
during infusion of angiotensin (2, 4, and 8 ng/kg min-i, respectively). Aldosterone was not estimated at the highest dose. Solid
lines indicate 5-Val-angiotensin U, and broken lines indicate 5lle-angiotensin II.
ments in mean blood pressure (Fig. 2). In both subjects, 5-Ile-angiotensin II was associated with
somewhat g r e a t e r increments in plasma
aldosterone for a given plasma angiotensin II concentration. This aspect seems worthy of further
study.
Effect of Angiotensin II Infusion on the Half-Life
of Aldosterone. — The half-life of injected
aldosterone was 29.7 minutes before infusion of
angiotensin II and 30.3 minutes during infusion of
angiotensin II. Ford et al. (23) have reported that
the metabolic clearance rate of aldosterone appears to be unaffected by sodium deprivation.
Therefore, it was assumed that changes in plasma
aldosterone in the present study reflected changes
in aldosterone secretion.
MAIN EXPERIMENT
Effect of Sodium Depletion on the Pressor and
Aldosterone Responses to Angiotensin II.—
Detailed^ results are given in Table 1. Cumulative
72
OELKERS, BROWN, FRASER, LEVER, MORTON, ROBERTSON
Plasma 11-hydroxycorticosteroids were also significantly higher in sodium depletion than they
were in sodium repletion (18.12 ± 5.9 /ug/100 ml in
sodium depletion and 14.76 ± 4.4 /Ag/100 ml in
sodium repletion; paired £=2.82, P<0.0l). This
difference was greatest under basal conditions. A
fall in plasma 11-hydroxycorticosteroids occurred
during administration of angiotensin; the sodiumdeplete values remained only slightly higher than
the corresponding sodium-replete values, and the
difference was of borderline significance (paired t
= 1.88,0.05 < P<0.l).
In all five subjects, the basal plasma concentrations of angiotensin II and aldosterone were distinctly elevated after sodium depletion.
The response of plasma aldosterone to infusion
of angiotensin II was very similar in subjects 1-4
TABLE 1
Details of Biochemical Data, Blood Pressure, and Heart Rate
Plasma
3
4
5
39
28
2
4
8
65
134
207
81
130
373
0
0
78
69
14.5
13.5
22
18
17.5 20
17
30
35.5 46
32.5 73
5
D
R
D
R
D
4.2
4.1
4.0
4.1
4.1
3.9
4.0
4.1
2.1
1.9
.9
i2.1
L.9
2.0
2.0
2.2
2.1
2.1
108/71
114/67
60
65
111/77
116/80
123/86
114/Y2
117/77
120/85
61
60
60
64
66
62
97/65
92/58
65
74
104/73
113/82
122/89
92/62
94/66
101/71
66
68
68
68
75
80
86/60
93/69
62
61
92/67
100/96
105/82
97/76
105/80
111/88
61
62
62
66
62
65
103/72
106/72
76
80
2.1
2.2
2.2
113/78
117/85
125/92
105/76
110/80
118/87
74
72
73
71
73
73
2.3
2.3
2.3
2.3
2.3
99/69
93/70
65
60
109/81
115/87
123/94
94/72
96/73
97/76
64
64
65
62
61
60
10
9
8
140
139
139
139
140
141
139
139
141
141
3.6
3.8
3.7
3.5
3.7
3.3
3.4
3.4
3.6
3.8
!2.0
2.0
I 2.0
i2.0
1.9
2.2
2.0
2.2
2.1
2.1
20
16
14
16
16
136
136
133
134
133
140
139
137
137
137
4.0
4.2
4.4
4.2
4.0
4.1
4.3
4.4
4.4
4.5
22.0
S2.0
i2.0
!2.0
52.0
1.9
1.8
2.0
2.0
2.0
141
141
140
140
136
136
135
138
136
3.7
3.8
3.8
3.7
3.4
3.5
3.6
3.5
3.5
1.8
L.9
L.8
L.8
141
137
139
138
138
139
137
137
140
137
3.8
3.8
3.8
3.7
3.7
28
74
0
0
16
18
81
85
11
11
50
46
2
4
8
70
144
216
120
196
323
25
25
31
63
76
82
17
12
12
13
14
0
0
6
7
60
66
6
6
32
34
2
4
8
62
108
166
131
211
320
7
14
15
34
44
57
16
13
14
23
21
17
17
16
0
0
8
7
41
32
31
25
2
4
8
88
124
290
103
111
387
16
14
19
19
15
36
28
18
12
15
17.5
R
24
21
14
17
16
14
34
34.5 15
29
29
30
D
140
142
142
12
9
10
184
242
17
18
R
139
139
142
139
139
2
4
8
8.5
7.5
D
3.9
3.8
3.7
L.9
.9
L.9
Hear t rate
(min-1)
BP
(mm Hg)
Mg
' mEq/liter)
24
20
14
10
8
6
92
190
359
27.5 38
23.5 75
CO CO
CD 00
17
13
R
1
(mEq/liter)
to to
2
0
0
Na
(mEq/liter)
00 O5
CO CO
1"
All infusion Arterial All Aldosterone 11-OHCS
rate
(pg/ml)
(ng/100 ml) ( M g/100ml)
(ng/kgmin"1) _
D
R
R
D
D
to to
O O)
Subject
CD CO
CO CO
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sodium losses (urinary output minus dietary intake)
induced by furosemide and 3 days of low-sodium
intake in the five subjects were 105, 247, 97, 146,
and 144 mEq, respectively. Cumulative potassium
balances similarly computed were - 9 , -103, -68,
25, and 53 mEq, respectively. There was no significant difference in the plasma concentration of
sodium or potassium before and after sodium
d e p l e t i o n : the sodium concentration was
138.54 ± 2.57 (SD) mEq/liter before depletion and
138.50 ± 1.82 mEq/liter after depletion, and the
potassium concentration was 3.89 ± 0.24 mEq/liter
before depletion and 3,83 ± 0.35 mEq/liter after
depletion. Plasma magnesium was distinctly elevated in sodium depletion (1.94 ± 0.08 mEq/liter
before depletion and 2.10 ± 0.13 mEq/liter after
depletion; paired t= 4.16, P<0.00l).
R = sodium replete, D — sodium deplete, All = angiotensin II, and 11-OHCS — 11-hydroxycortieosteroids. If no value is given the
sample was lost.
"For each subject the significance of the change in slope of the angiotensin II-aldosterone dose-response curve was assessed by the
F-test for equality of regression slopes. Subject 1: F - 19.46, df- 1,6, P< 0.01; subject 2: F = 2.86, df- 1,4, NS; subject 3: F - 30.71,
df= 1,6, P< 0.001; subject 4: F - 11.21,df- 1,6, P< 0.025; subject 5: F - 2 . 8 5 , d f - 1,6, NS.
Circulation Research, VoL XXXIV, January 1974
ANGIOTENSIN II AND ALDOSTERONE
PLASMA
ALDOSTERONE
ng/ioOmi
8070605040Downloaded from http://circres.ahajournals.org/ by guest on June 18, 2017
302010-
10
20 30 40 50
100
200 300400
ART. PLASMA ANGIOTENSIN D (pg/ml)
FIGURE 3
Concurrent arterial plasma angiotensin II and plasma
aldosterone concentrations before (solid circles) and after (open
circles) sodium depletion in subject 3. Abscissa is a log scale.
Basal samples correspond to the two lowest replete and the two
lowest deplete angiotensin 11 values (Table 1). The difference in
slope of the two curves is highly significant on F-test (P < 0.001).
This difference was also apparent in the zone of overlap
(Pi 0.05).
(Table 1); subject 5 differed and is discussed separately. In subjects 1-4, the administration of
angiotensin II caused a clear increase in plasma
aldosterone in both states of sodium balance, with a
highly significant correlation between concurrent
measurements of the two substances (replete
r = 0.725, P< 0.001, and deplete r - 0.795,
P< 0.001). The dose-response curves after sodium
depletion were distinctly steeper however (Fig. 3);
the individual changes in slope were statistically
significant in subjects 1, 3, and 4. The same
phenomenon was apparent in subject 2, but unfortunately the loss of two samples prevented it from
being demonstrated statistically.
In sodium repletion, the biggest increments in
aldosterone were observed at angiotensin infusion
rates of 2 or 4 ng/kg min~', with little or no addiCirculation Research, Vol. XXXIV, January 1974
73
tional rise in aldosterone at the highest dose (8 ng/
kg min1) in any subject. By contrast, following
sodium depletion, substantial increments in
aldosterone were seen at all angiotensin infusion
rates; two subjects showed the greatest increases at
the highest rates of angiotensin infusion. This observation suggests, but does not establish, that the
highest angiotensin and aldosterone values of
sodium repletion occurred at or near the upper end
of the sigmoid dose-response curves. By contrast,
after sodium depletion, the highest points seen
were still on the steep part of the respective
curves.
Subject 5 had a very flat dose-response curve
both before and after sodium depletion and
showed a slightly anomalous blood pressure
response.
In all five subjects, the basal plasma aldosterone
concentrations were higher for the concurrent
plasma angiotensin II levels after sodium depletion
than those that would have been predicted from
the dose-response curves of the sodium-replete
state.
The pressor dose-response relationship to
angiotensin II was altered differently by sodium
depletion. The average mean basal blood pressure
in the five subjects was 77.6 ± 5.7 (SD) mm Hg during sodium repletion and 78.0 ± 5.7 mm Hg after
sodium depletion. As in previous studies, the
pressor effect of infused angiotensin was
diminished by sodium depletion. The relationship
between the arterial plasma angiotensin II concentration and the change in mean arterial blood
pressure for individual subjects is shown in Figure
4. In sodium repletion this relationship appeared to
comprise the lower parts of the sigmoid doseresponse curves where near-maximal responses
had not been attained. The shape of these curves
indicated that in such circumstances fluctuations of
arterial plasma angiotensin II within the normal
range of 5 to 35 pg/ml were not likely to influence
the arterial blood pressure by more than 10 mm Hg
via a direct pressor effect. In sodium depletion, a
roughly parallel shift of the curves to the right was
seen in all cases, but in subject 5 (Table 1), who had
a shallow angiotensin II-aldosterone dose-response
curve in sodium depletion, the pressor curve was
distinctly flat.
Changes in the blood pressure and the
aldosterone response threshold were less easy to
interpret. The increments in arterial plasma
angiotensin II necessary to produce a 5-ng/100 ml
increase in plasma aldosterone ranged from 6 to 77
74
OELKERS, BROWN, FRASER, LEVER, MORTON, ROBERTSON
A MEAN BP
(mm Hg)
25-1
20-
• Na Replete
O No Deplete
15-
10-
5-
0J
200 300 400
ARTERIAL ANGIOTENSIN M (pg/ml)
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FIGURE 4
Individual response curves of mean blood pressure (BP) to arterial plasma angiotensin H before (solid circles) and after
(open circles) sodium depletion in the five subjects of the main
experiment. Abscissa is a log scale.
pg/ml (mean 36, N = 5) in sodium repletion and
from 14 to 107 pg/ml (mean 58, N = 4) in sodium
depletion. The remaining sodium-deplete subject
(no. 5) did not reach a threshold level. The corresponding increments in arterial angiotensin II required to increase mean arterial blood pressure by
5 mm Hg ranged from 15 to 43 pg/ml (mean 28) and
from 67 to 360 pg/ml (mean 150). The change in
threshold in sodium depletion was not statistically
significant for either the aldosterone or the blood
pressure response.
Discussion
The present experiments have shown that the
aldosterone and the pressor dose-response curves
to arterial plasma angiotensin II infusions are
modified in contrasting ways in sodium depletion in
man. The magnitude of the sodium deficit in these
experiments was slightly more than that observed
in normal subjects after 5 days of dietary sodium
deprivation (24, 25) and, thus, seemed physiologically relevant. More severe sodium deficiency
is difficult to achieve by dieting because of the
efficiency of renal sodium conservation.
In four of the five subjects examined, sodium
depletion was accompanied by a distinct steepening of the aldosterone dose-response curve to
angiotensin II. In these studies there was no evidence of a modification of aldosterone metabolic
clearance by the infusion of angiotensin II; consequently, the changes in plasma aldosterone con-
centration probably reflected corresponding
changes in the aldosterone secretion rate. No obvious systematic changes in plasma aldosterone or
angiotensin II concentrations were seen after 1
hour of infusing a given dose of angiotensin.
Therefore, 1 hour appeared to be an adequate time
for the establishment of a steady state.
The mechanism for the sensitization of the
adrenal cortex to angiotensin II remains to be
determined. No significant changes in plasma
potassium concentration occurred, and cumulative
potassium balance was negative in three of the five
subjects. The only person who did not show a clear
increase in sensitivity following sodium depletion
(no. 5) had a calculated positive potassium balance
of 53 mEq.
Similarly, plasma sodium concentration did not
change significantly in the 3 days of sodium
deprivation in contrast to the distinct fall seen in
normal subjects deprived of sodium for 5 days (24).
This finding does not exclude the possibility that
sodium deficiency acts more subtly on the adrenal
cortex in the absence of detectable changes in
plasma sodium or potassium concentration.
A highly significant increase in plasma magnesium concentration was observed in sodium
depletion in the present experiments, but the physiological importance of this finding remains uncertain. Studies in man (26), rat (27), and dog (28, 29)
have suggested that a rise in plasma magnesium
probably would not stimulate aldosterone secretion. However, this possibility deserves further examination. Many protein and polypeptide hormones appear to owe their effects to a stimulation
of adenyl cyclase activity (30). Adrenocorticotropin (ACTH) (31, 32) and angiotensin II (33)
are not exceptions. Magnesium ions are essential for
the functioning of this cyclase system (34) and for
other cyclases (35). Variations in the plasma concentrations of magnesium may therefore influence
the adrenal response to ACTH and angiotensin.
The increase observed in plasma 11-hydroxycorticosteroid concentration in sodium deficiency suggested the possibility of a rise in the circulating
ACTH level in this situation. The fluorometric
method (21) used to estimate 11-hydroxycorticosteroids detects cortisol, corticosterone and a
number of other compounds (36). Boyd et al. (11),
• using the same method, also found an increase in
plasma 11-hydroxycorticosteroid concentration in
sodium depletion; however, this increase was not
evaluated statistically. In the present paper, the
elevation in plasma 11-hydroxycorticosteroids in
Circulation Research. Vol. XXXIV. January 1974
75
ANGIOTENSIN II AND ALDOSTERONE
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sodium depletion relative to the level in sodium
repletion was most marked under basal circumstances but became less marked during infusion of
angiotensin II. In both situations a significant fall in
plasma 11-hydroxycorticosteroid concentration occurred during the administration of angiotensin.
However, this fall was not necessarily a consequence of the administration of angiotensin,
because the experiments were conducted between
8 AM and 1 PM when an endogenous fall in plasma
cortisol is usual. Rayyis and Horton (37) have reported that administration of angiotensin II in man
causes a rise in circulating ACTH, although this rise
is accompanied by a fall in plasma 11-hydroxycorticosteroids. This decrease in 11-hydroxycorticosteroids was estimated by a competitive protein-binding method. After suppression of ACTH
by dexarnethasone, angiotensin II caused only a
minimal rise in aldosterone. This study (37) clearly
indicates the importance of ACTH in the
adrenocortical response to angiotensin II. Previous
work (38) has shown that physiological increases in
ACTH levels may cause a marked rise in plasma
aldosterone concentration in sodium-deplete
human subjects. Therefore, it is possible that
ACTH released in response to angiotensin II infusion may contribute to the changes in plasma
aldosterone seen in the experiments reported in
this paper.
Another possibility, which has been considered
by Ganong et al. (39), is that angiotensin may have
a trophic effect on the adrenal cortex. According to
this theory, exposure to high circulating levels of
angiotensin II for several days, as occurs in sodium
depletion (9, 14, 18, 24), might enhance the biosynthetic potential possibly by inducing hypertrophy of the zona glomerulosa; therefore, further increments of angiotensin II would have an increased
effect on aldosterone secretion.
Finally, there remains the possibility that an unidentified hormone is responsible for the sensitization of the adrenal cortex to angiotensin II. Dale
and Melby (40) have recently isolated a 16-a-hydroxy derivative of 18-hydroxy-deoxycorticosterone from human adrenal glands and,
although this derivative seems unlikely to possess
marked mineralocorticoid activity, it indicates the
presence of unstudied pathways of steroid metabolism that may yield important hormonal compounds.
Whatever the precise mechanism for the sensitization of the adrenal cortex to angiotensin II in
sodium deficiency turns out to be, the present studCirculation Research. Vol. XXXIV, January 1974
ies indicate an important role for the reninangiotensin system in the control of aldosterone
secretion in man. As suggested previously (41, 42)
the divergent effects of angiotensin II on
aldosterone and blood pressure facilitate sodium
conservation under these circumstances. Not investigated in this paper, but possibly of equal importance in the regulation of sodium balance, are the
direct actions of angiotensin II on the kidney (43,
44).
Acknowledgment
We are indebted to the subjects who volunteered for these
studies, to Dr. D. A. Smith for performing the plasma magnesium
estimations, and to Dr. Gisela Diisterdieck and Dr. R. H. Chinn
for much practical assistance.
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Sensitization of the Adrenal Cortex to Angiotensin II in Sodium-Deplete Man
WOLFGANG OELKERS, JEHOIDA J. BROWN, ROBERT FRASER, ANTHONY F. LEVER,
JAMES J. MORTON and J. IAN S. ROBERTSON
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Circ Res. 1974;34:69-77
doi: 10.1161/01.RES.34.1.69
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