(Hypertension. 2000;36:862.)
© 2000 American Heart Association, Inc.
Scientific Contributions |
From the Third Department of Internal Medicine, Fukui Medical University, Fukui, Japan.
Correspondence to Haruhiko Hatakeyama, MD, Third Department of Internal Medicine Fukui Medical University, 23-1 Matsuoka-cho, Fukui 910-1193, Japan. E-mail haru{at}fmsrsa.fukui-med.ac.jp
| Abstract |
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Key Words: adrenocorticotropic hormone gene expression gene regulation hormones hypertension, essential
| Introduction |
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Previous studies showed that the administration of ACTH (1-24) caused
an increase in blood pressure in normotensive and hypertensive
subjects, whereas no change was observed in patients with adrenal
insufficiency,4 and the effect of ACTH (1-24) was mimicked
by cortisol.5 Thus, the rise in pressure has been believed
to be due to ACTH-induced increases in cortisol secretion in the
adrenal gland.6 It has been shown that the direct effect
of cortisol on vascular tone plays a significant role in the rise in
pressure, because the steroid may raise pressure in the absence of any
classic glucocorticoid effects (increases in plasma volume or urinary
sodium retention).7 Cortisol increases vascular tone by
potentiating the vasoconstrictor action of a number of pressor
hormones, including
-adrenergic agonists and angiotensin
II.8 9 In addition to the hormonal effect, ACTH has been
suggested to have direct effects on vascular tone. In hypovolemic and
hemorrhagic shock in humans, acute intravenous
administration of ACTH (1-24) promptly restores blood pressure without
any effect on heart rate.10 However, little is known
concerning the existence of ACTH-R in the vasculature.
11ß-Hydroxysteroid dehydrogenases (11ß-HSDs) interconvert cortisol and its inactive metabolite, cortisone, in humans. We have demonstrated that the local glucocorticoid metabolism displayed by 11ß-HSD within the vascular wall may be important in the control of vascular tone and the pathogenesis of hypertension.11 In humans, two 11ß-HSD isozymes have been described and cloned. The first enzyme (11ß-HSD1) mainly catalyzes oxygen reduction (cortisone to cortisol) and is a low-affinity NADP(H) enzyme.12 A second isozyme (11ß-HSD2) is a high-affinity NAD-dependent enzyme and catalyzes only 11ß-dehydrogenation (cortisol to cortisone).13 The diminished dehydrogenase activity was reported in patients with essential hypertension14 and in resistance vessels of genetically hypertensive rats.15 We have demonstrated that impaired 11ß-HSD2 activity in the vascular wall could result in increased vascular tone by enhancing the effect of cortisol.11
The purpose of the present study was to clarify the physiological and pathophysiological significance of ACTH-R in human vessels. We investigated the gene expression in human aortic endothelial cells (HAECs). Furthermore, to assess its potential role in the control of blood pressure, the effect of ACTH (1-24) on vascular 11ß-HSD activity was also examined.
| Methods |
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RT-PCR Method
Oligonucleotide primers
(Table) for reverse transcriptase
(RT)polymerase chain reaction (PCR) were synthesized with an Applied
Biosystems model 392 DNA synthesizer and purified with
oligonucleotide purification columns. RT-PCR was
performed as described previously.16 A 10-µL aliquot of
each RT-PCR reaction mixture was electrophoresed on a 2% agarose gel.
The gel was stained with ethidium bromide and photographed. Each
experiment was repeated 3 times, and the data shown are
representative of those obtained in 3 experiments.
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Northern Blot Analysis
Total RNAs (30 µg) isolated from confluent culture of HAECs
were electrophoresed on 1.5% agarose gel containing 1.1 mol/L
formaldehyde, blotted onto Hybond N+ nylon
membrane, and hybridized at 42°C for 20 hours in 50% formamide, 5x
saline/sodium/phosphate/EDTA, 5x Denhardts solution, 0.5% SDS, and
0.4 mg/mL salmon sperm DNA containing 5 ng/mL human ACTH-R cDNA, which
had been labeled with [
-32P]dCTP to a
specific activity of
1x109 cpm/µg. The cDNA
probe (631 bp) was originally obtained by RT-PCR with adrenal gland
total RNA as described above. The sequence was verified by the dideoxy
chain termination method. After hybridization, the membrane was washed
twice with 2x standard saline citrate and 0.1% SDS at room
temperature and then twice with 0.1x standard saline citrate and 0.1%
SDS at 42°C and autoradiographed. The hybridized signals were
analyzed with a BAS 1500 Bioimaging Analyzer.
Assay of 11ß-HSD Activity
11ß-HSD activity was measured by a radiometric conversion
assay as previously described.17 In brief, confluent HAECs
were incubated in a hydrocortisone-free and serum-free medium
containing 10 nmol/L [1,2,6,7-3H]cortisol for 8
hours, after which steroids were extracted with chloroform and were
resolved by thin-layer chromatography. Radioactivities
corresponding to cortisol and cortisone were determined. Dehydrogenase
activity was calculated as follows: counts per minute for
cortisone/(counts per minute for cortisol+counts per minute for
cortisone)100.
Competitive PCR Method
Single-stranded cDNA was prepared with total RNA (1 µg) from
HAECs as described previously.16 The single-stranded cDNA
was used in competitive PCR. The sequences of sense and antisense
primers for 11ß-HSD2 were the same as in the Table. The
competitive templates were made with a PCR MIMIC Construction Kit
(Clontech Laboratories, Inc). After quantification, a series dilution
was used as an internal standard for competitive PCR. Competitive PCR
was performed with 20 µL of the reverse-transcribed DNA, 2 µL of
different concentrations of the competitive template, 0.5 µmol/L
each of sense and antisense primers, and 0.5 U of Taq DNA
polymerase (TaKaRa) in 50 µL of 10 mmol/L Tris-HCl (pH
8.3), 50 mmol/L KCl, 2 mmol/L MgCl2,
and 0.2 mmol/L of each deoxy-NTP. The reactions were performed for
30 seconds at 94°C, 30 seconds at 69°C, and 1 minute at 72°C for
35 cycles. Aliquots of 10-µL amplification products were
electrophoresed on a 2% agarose gel. The gel was stained with ethidium
bromide and photographed. The signal intensity was quantified by
computerized densitometry with the use of the BIO-PROFIL BIO-1D system
(Compak). The intensities of the products from cDNA and from
competitive templates were plotted as a function of the known amounts
of the competitive templates. The intra-assay and interassay
variabilities of the competitive PCR method were 13.5% and 17.3%,
respectively.
Statistical Analysis
Data are expressed as mean±SEM. The significance of differences
was assessed by 1-way ANOVA followed by the Student-Newman-Keuls
multiple comparison test. Values of P<0.05 were accepted as
statistically significant.
| Results |
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11ß-HSD Expression in HAECs
Next, we examined the expression of 11ß-HSD1 and 11ß-HSD2
genes in HAECs. With the use of the RT-PCR method, amplified
products corresponding to transcripts of the 11ß-HSD2 gene were
detected (Figure 3B). However, the HAECs
showed no detectable 11ß-HSD1 mRNA with the conditions used (Figure 3A). Cloning and sequence analysis of the PCR
products demonstrated that these bands had the known sequences of
human 11ß-HSD mRNAs (data not shown).
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Effect of ACTH (1-24) on 11ß-HSD2 Gene Expression
To investigate the effect of ACTH (1-24) on 11ß-HSD2 gene
expression, we conducted a competitive PCR analysis.
Representative results for the 11ß-HSD2 expression
are shown in Figure 4. The signals of
endogenous 11ß-HSD2 cDNA increased with the serial
dilution of the competitive template. For ACTH (10 nmol/L)treated
HAECs, the point of equivalence of signals was at the 10-fold diluted
mimic. The result indicates that ACTH (10 nmol/L) caused an
10-fold
decrease in the amount of 11ß-HSD2 mRNA level. More exact
quantification in the presence of 2-fold serial diluted mimics revealed
that ACTH (1 nmol/L) reduced
4-fold the level of 11ß-HSD2 mRNA
(data not shown). Because the amount of 11ß-HSD1 mRNA in HAECs was
below the detectable level, we did not attempt to examine the effect on
11ß-HSD1 expression.
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Effect of ACTH (1-24) on 11ß-HSD Activity
Incubation with cortisol resulted in moderate (30±3%) conversion
to cortisone in HAECs (Figure 5). Next,
we investigated the effect of ACTH (1-24) on 11ß-HSD activity. The
tested ACTH concentrations included the
physiologically and
pathophysiologically relevant ranges. As shown
in Figure 5, ACTH (1-24) induced dose-dependent decreases in the
dehydrogenase activity of HAECs, with a maximal decrease (78±6%) at
10 nmol/L. The inhibitory effect of ACTH (1-24) on the
dehydrogenase activity was dose-dependently reduced in the presence of
ACTH (7-38), a selective ACTH-R antagonist. This result
indicates that ACTH (1-24) reduces the dehydrogenase activity of HAECs
through an interaction with its own receptor.
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| Discussion |
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ACTH regulates cortisol synthesis in the adrenal cortex. The cortisol is important in the control of vascular tone. The cortisol action may be modified by vascular 11ß-HSD activities. We have demonstrated that the dehydrogenase activity (cortisol to cortisone) in human vascular cells is mediated by 11ß-HSD2 and that the reduced activity may be relevant to the pathogenesis of hypertension.11 The present study clarified that ACTH downregulates the expression of 11ß-HSD2, suggesting that this peptide plays a significant role in the control of vascular tone through an interaction with the vascular receptor. This may be compatible with the fact that peripheral conversion of cortisol to cortisone in the kidney is inhibited by ACTH and that the marked increase of cortisol/cortisone ratio is observed in urine and plasma during ACTH infusion but not after hydrocortisone infusion in humans.18 19 Diederich et al20 reported that 11ß-HSD activity in human kidney slices was not influenced by incubation with increasing doses of physiological ACTH (1-39) for 1 hour. Because ACTH-R is not expressed in the kidney1 and because the authors examined a fast effect of ACTH on renal 11ß-HSD activity, their study may not be contradictory to our results.
Brem et al21 reported that two 11ß-HSD isozymes were expressed in rat aortic endothelial cells and that these cells possessed a predominant oxygen reductase activity. Our results demonstrated that HAECs expressed no detectable 11ß-HSD1 mRNA. The difference of species might account for the observed differences. Because dehydrogenase activity has been demonstrated to play a significant role in conferring the mineralocorticoid specificity on the type 1 mineralocorticoid receptor, the predominant dehydrogenase activity in the present study may be related to the presence of much higher levels of the receptor in human blood vessels. Comparative levels of the receptor in various vessels are to be examined in further investigations.
The blood pressureraising effect of ACTH has been known since its
introduction into clinical practice. Indeed, hypertension is a crucial
feature of patients with Cushings disease and ectopic ACTH syndrome.
Exogenous ACTH (1 mg/d) administered to normotensive subjects can also
raise their blood pressures by
20 mm Hg over the treatment
period.4 When ACTH is given by constant
intravenous infusion, rates as low as 50 µg/d raise
pressure. ACTH concentrations rose with the infusion but remained
within the normal range, suggesting that concentrations achieved under
physiological conditions could be sufficient to
raise blood pressure in humans.22 The effect of ACTH has
been postulated to be caused by ACTH-induced increases in cortisol
production in the adrenal cortex. Our results indicate that
ACTH could enhance blood pressure not only by regulating the
production of cortisol in the adrenal cortex but also by
enhancing the effect of cortisol on vascular tone through the adrenally
independent mechanism. The present study may provide the starting
point for a novel understanding of the molecular basis of
hypertension.
| Acknowledgments |
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Received February 17, 2000; first decision March 14, 2000; accepted May 19, 2000.
| References |
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