Vol.
177,
May
31, 1991
No.
1, 1991
BIOCHEMICAL
BIOPHYSICAL
RESEARCH
COMMUNICATIONS Pages
ENDOTHELIN-1
tNDUCES AORTIC Janos
Departments University Received
AND
March
PROSTACYCLIN ENDOTHELIAL
RELEASE CELLS
FROM
G. Filep l*, Bruno Battistini I, Yvan P. C&e Adrien R. Beaudoin * and Pierre Sirois 1
of 1 Pharmacology and * Biology, of Sherbrooke, Sherbrooke, P.Q., 27,
Faculty Canada
171-176
BOVINE
*,
of Medicine, JlH 5N4
1991
SUMMARY: The effects of endothelin-1 (ET-l) on the release of prostacyclin from cultured bovine aortic endothelial cells were studied. ET-l induced a timeand dose-dependent release of 6-keto PGF,,, the stable metabolite of prostacyclin, with an apparent EC,, value of 3.0 kO.9 nM (n=6). ET-l up to a concentration of 500 nM did not affect cellular integrity. Preincubation of the cells for 30 min with 10 FM indomethacin inhibited ET-l (100 nM) - induced prostacyclin release by 90 % . These findings indicate that ET-l can directly stimulate prostacyclin release from endothelial cells probably through a receptor mediated mechanism. 0 1991Academic Press.Inc.
Endothelin-1 vascular
(ET-l)
endothelial
first isolated from conditioned
cells (1) is now well characterized
medium of cultured
as a potent constrictor
of vascular
and non-vascular
smooth muscles both in vivo and in vitro (c.f. 2).
In addition
to its contractile
action,
aggregation
ET-l
has been shown to inhibit ex vivo
of rabbit platelets (3) as well as in vivo platelet aggregation
in the
dog (4) and rabbit (5), whereas it has no effect on in vitro platelet aggregation (3,4). ET-l,
Since indomethacin the
involvement
presumably
prostacyclin,
supported
of
an
antiaggregatory
cyclooxygenase
has been suggested
(3,4).
This
by the findings that the in vivo anti aggregatory
dog was accompanied hydrolytic
and aspirin can block the antiaggregatory
metabolite
by enhanced
plasma
of prostacyclin
levels
(4). The
* To whom correspondence
product, is further
action of ET-l in the of 6-keto
present
designed to study the effects of ET-l on prostacyclin
view
action of
PGF,,,
experiments
the were
release from monolayer
should be addressed. 0006-291X/91 171
$1.50
Copyight 0 1991 by Academic Press, Inc. AlI rights of reproduction in any form reserved.
Vol.
177,.
No.
of cultured thrombin,
1, 1991
BIOCHEMICAL
endothelial a potent
cells
stimulus
AND
BIOPHYSICAL
and to compare of prostacyclin
MATERIALS
RESEARCH
the effects synthesis
COMMUNICATIONS
of ET-l
to those
of
(6).
AND METHODS
-and
chemicals. Synthetic endothelin-1 (ET-i, Peninsula Labs, Belmont, CA) was dissolved in distilled water and further diluted in 0.15 M NaCl. Thrombin (Thrombostat) was purchased from Parke Davis, Scarborough, Cnt. lndomethacin (Merck Frosst, Montreal, Canada) was dissolved in ethanol and diluted with 0.15 M NaCI. The final concentration of ethanol in the culture medium was 0.5 %. Medium 199 and lactate dehydrogenase kit were purchased from Sigma Chemical Co., St. Louis, MO; fetal calf serum from Gibco, Grand Island, N.Y. and 6-keto PGF,, antiserum from Cayman Labs, Ann Arbor, MI.
Endothelial cell culture. Bovine aortic endothelial cells were obtained from collagenase-treated (300 U/ml for 15 min at 37°C) bovine aortae (9), seeded in T 75 culture flasks (Falcon) and grown in Medium 199 supplemented with 15 % fetal calf serum (heat inactivated at 56°C for 30 min), L-glutamine 2 mM, penicillin 100 U/ml, streptomycin 0.1 mg/ml and fungizone 2.5 pg/ml. After achieving confluence, the cells were detached by using EDTA/trypsin treatment (0.4 mnn / 0.04 % in HBSS without Ca*+ and Mg*+) for 3 min at 37”C, and were subcultured for up to four times. The cells were finally seeded in 6-well plates (Falcon) with the same medium. The identity of endothelial cells grown in this fashion was verified by morphology and by demonstration of angiotensin-converting enzyme activity. The viability of cells was greater than 95 % as assessed by trypan blue exclusion. Experimental protocols. When the cells reached confluence, the culture medium was replaced 8 h before the experiments. Cells were incubated for the indicated time period with ET-l (0.1-500 nM), thrombin (0.01-0.1 U/ml) or their vehicle.. ET-l concentrations higher than 500 nM were not studied because of the limi,ted availability of the peptide. In the experiments with indomethacin, the endothelial cells were preincubated for 30 min with 10 FM indomethacin before challenge with 100 nM ET-l. Only one concentration of agonists was added to each well. At the end of the incubation period, aliquots of the medium were removed to determine concentrations of 6-keto PGF,,, the stable metabolite of prostacyclin and lactate dehydrogenase activity, respectively. The samples for 6-keto PGF,, were stored at - 20°C until assayed. Lactate dehydrogenase activity was measured on the day of the experiments using a commercial kit. Concentrations of 6-keto PGF,, were Measurement of 6- keto PGF,,. measured by a direct enzyme immunoassay according to the method of Pradelles et al.(8) . The detection limit of the assay was 0.3 pg/tube. lntrassay and interassay coefficients of variation were 5.6 % (n=5) and 9.4 % (n=4), antiserum cross-reacted with PGF, 12 %, respectively. The 6-keto PGF,, 6,15-diketo PGF,, 8 % and TXB, 0.2 %. Prostacyclin production was calculated as the difference between the amount of 6-keto PGF,, released by cells challenged with the agonist minus the amount released by identically treated but unchallenged cells. 172
Vol.
177,
No.
BIOCHEMICAL
1, 1991
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
Statistical analvsis. Values are reported as means +SEM. Statistical analysis of the data was performed by Dunn multiple contrast hypothesis test (9) or by Mann-Whitney U test. A p < 0.05 level was considered significant for all tests. RESULTS EndothelinInitial prostacyclin (Fig.1).
l-induced studies from
cultured
with
thrombin
be equivalent
effect
was
in prostacyclin (Fig.1).
that
bovine
prostacyclin
and the maximal
release
demonstrated
Enhanced
of changes
prostacyclin
endothelial
production reached release
to that of 0.03-0.04
was observed
was
U/ml
is capable
of releasing
cells in a time-dependent
within
The stimulatory
Thrombin,
100 nM ET-1
at 1 min of incubation,
15 min (Fig.?). observed
effect
when
manner
Similar cells
of 100 nM ET-l
time course
were was
stimulated
calculated
to
of thrombin.
0.1 U/ml
I
1 ET-l,
1 Thrombin, I
100
nM
P
E 3
0.01 U /ml
4
i
cmi;p 5o 6o 01 O ‘O 2oT?e
0
2
0 ”
10
9
ET-1 [
Log M ]
8
7
Fia. 1. Time course of 6-keto PGF,, release from cultured bovine aortic endothelial cells by endothelin-I (ET-l) and thrombin. Cells were seeded in 6-well plates, incubated in 1.9 ml of incubation medium and were stimulated with ET-1 (100 nM) or thrombin (0.01 and 0.1 U/ml). At the indicated times an aliquot was removed for determination of 6-keto PGF,, concentration.
Values
were calculated as the difference between 6-keto PGF,, levels in the medium of stimulated cells minus that of identically treated but unstimulated cells. Values are means r SEM of 3-6 separate experiments in triplicate. Fig. 2. Effect of endothelin-7 (ET-j) on 6-keto PGF,, production and lactate dehydrogenase (LDH) release by cultured bovine aortic endothelial cells. The culture and experimental conditions were identical to those described in the legend to Fig.1. Cells were stimulated with various concentrations of ET-1 for 15 min, then aliquots of the medium were removed for determination of 6-keto PGF,, concentration and LDH activity. The 6-keto PGF Icr production was calculated as the difference between the amount released by stimulated cells minus that of identically treated but unstimulated cells. Values are means + SEM of 6 separate experiments in triplicate. x, p < 0.05; xx, p < 0.01 (compared to control by Dunn multiple contrast hypothesis test). 173
6
Vol.
177,
No.
1, 1991
When
BIOCHEMICAL
cells were
a dose-dependent
exposed
increase
concentration
as low
levels
ET-l
up to a concentration
release
(Fig.2).
from
Inhibition release
was
induced
induced
EC,,
prostacyclin
set of experiments,
prostacyclin
in
released
release
absence
observed
of ET-l, (Fig.2).
increase
was
At a
in 6keto
3.0 20.9 nM (n=6).
lactate
dehydrogenase
by indomethacin
of 100 nM ET-l
and
presence
on prostacyclin
of
indomethacin.
10 PM indomethacin
on average
inhibited
lactate
n=4,
p < 0.05).
dehydrogenase
ET-l
-
by 90 % (520 ? 82 and 49 + 20 pg
by 250 000 cells per 15 min in the absence
respectively,
affected
was
significant
the effect
the
formation
of indomethacin,
concentrations
value for ET-l
of the cells for 30 min with
PGF,,
vehicle
ET-l
release
COMMUNICATIONS
(Fig.2).
compared
Preincubation
RESEARCH
of 500 nM did not affect
of ET- l- induced
In another
6-keto
in prostacyclin
The apparent
the cells
BIOPHYSICAL
for 15 min to increasing
as 1 nM,
PGF,,
AND
Neither
release
(data
and presence
indomethacin
nor its
not shown).
DISCUSSION The
present
study
dose-dependent
release
metabolite,
6-keto
Significant
prostacyclin
l-10
nM.
These
vivo platelet course
PGF,,,
must not
dehydrogenase
cellular
release,
completely
blocked
enhanced
prostacyclin of ET-l
interaction specific
on the specific further
support
ET-l
that
receptor binding
as
and
antagonists of ET-l
cells,
its putative presently to brain
to this view. 174
to inhibit (4).
Similarly
without for
addition
lactate nearly that
to a non-specific
it was
a consequence
membrane
receptors.
capillary
that ET-
indicate
are not available, endothelial
of
prostacyclin
unchanged
release
in
The time
that indomethacin
be attributed rather
cells.
acid. The findings
prostacyclin
cannot
release
by
stable
as low as
reported
the substrate
evidenced
and
endothelial
production
with the observation
- induced
ET-l
major
to that of thrombin.
arachidonic
viability,
formation
aortic
to those
was similar
indicating
coupled
time-,
by its
prostacyclin
prostacyclin
on endothelial
between ET-l
by ET-l
acid,
induce
detected at ET-l concentrations
have been endogenous
affect
bovine
or to induce
stimulated
arachidonic
synthesis 1 did
release
can
as measured
are comparable
(3-5)
ET-l
ET-l
cultured
was
concentrations
(6),
exogenous
from
release
of prostacyclin
that
of prostacyclin,
aggregation
to thrombin
action
demonstrates
the lytic
of the Although
recent cells
reports (10)
lend
Vol.
177,
No.
1, 1991
The which
BIOCHEMICAL
present
experiments
ET-l
can stimulate
can activate
phospholipase
prostacyclin
release
(4).
Stimulation
glomerular ET-l whether
ET-l
might
independent
synthesis.
A, came
with
ET-l
from
Indirect
administration
phospholipase Ca*+
concentration
phospholipase
mechanisms
reported
(11,12)
and in vivo
muscle
(13,14)
Presently
and
by adding
it is not known
via a G protein It is also
A, and C in endothelial
as it was
a sustained
demonstrated
(16).
by
that ET-l
reporting
smooth
acid.
A, directly
evidence
in vitro
A, in cultured
COMMUNICATIONS
on the mechanisms
experiments
[3H]-arachidonic
intracellular activate
RESEARCH
cells (15) has been subsequently
activates
by increasing
BIOPHYSICAL
little information
prostacyclin
of phospholipase
labeled
ET-l
give
following
mesangial
to cells
AND
or indirectly possible
that
cells by parallel
for vascular
smooth
muscle
but cells
(14). In summary, capable
of releasing
that ET-l
released
on the same mediate
the present
either
cells
and/or
prostacyclin
findings
provide
direct
from endothelial
cells.
by endothelial
and can induce
modulate
or other prostacyclin
its biological
actions,
evidence Thus,
blood-borne release, including
that
ET-l
is
one may assume cells (17) may act
which
in turn,
may
inhibition
of platelet
Research
Council
aggregation. ACKNOWLEDGMENTS: Canada
for financial
assistance. and Scientist
The authors support
and Ms.
JGF and PS are in receipt Award,
thank
the Medical
Solange
of a Medical
Cloutier Research
for expert Council
of
technical Fellowship
respectively. REFERENCES
1. 2. 3. 4. 5. 6. 7.
Yanagisawa, M., Kurihara, M., Kimura, S., Tomobe, Y., Kobayashi, M., Mitsui, Y., Yazaki, Y., Goto, K. and Masaki, T. (1988) Nature 332, 411-415. Yanagisawa, M. and Masaki, T. (1989) Biochem. Pharmacol. 38, 1877-1883. Thiemermann, C., Lidbury, P., Thomas, R. and Vane, J. (1988) Eur. J. Pharmacol. 158, 181-182. Herman, F., Magyar, K., Chabrier, P.E., Braquet, P. and Filep, J. (1989) Br. J. Pharmacol. 98, 38-40. Thiemermann, C., May, G.R., Page, C.P. and Vane, J.R. (1990) Br. J. Pharmacol. 99, 303-308. Weksler, B.B., Ley, C.W. and Jaffe, E.A. (1978) J. Clin. Invest. 62, 923-930. Booyse, F.M., Sedlok, B.J. and Rafelson, M.F. (1975) Thromb. Diath. Haemorrh. 34, 825-839. 175
Vol.
8. 9. 10. 11.
12. 13. 14. 15. 16. 17.
177,
No.
1, 1991
BIOCHEMICAL
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
Pradelles, P., Grassi, J. and Maclouf, J. (1986) Anal. Chem. 57, 1170-l 173. Dunn, O.J. (1964) Technometrics 6, 241-252. Frelin, C., Ladoux, A., Marsault, R. and Vigne, P. (1990) J. Vast. Med. Biol. 2, 191. DeNucci, G, Thomas, R., D’Orleans-Juste, P., Antunes, E., Walder, C., Warner, T.D. and Vane, J.R. (1988) Proc. Natl. Acad. Sci. USA 85, 9797-9800. Filep, J.G., Battistini, B. and Sirois, P. (1990) Life Sci. 47, 1845-1850. Resink, T.J., Scott-Burden, T. and Buhler, F.R. (1989) Biochem. Biophys. Res. Commun. 158, 279-286. Reynolds, E.E., Mok, L.L. and Kurokawa, S. (1989) Biochem. Biophys. Res. Commun. 160, 868-873. Simonson, M.S. and Dunn. M.J. (1990) J. Clin. Invest. 85, 790-797. Axelrod, J., Burch, R.M. and Jelsema, C.L. (1988) Trends Neurol. Sci. 11, 117-123. Ehrenreich, H., Anderson, R.W., Fox, C.H., Rieckmann, P., Hoffman, G.S., Travis, W.D., Coligan, J.E., Kehrl, J.H. and Fauci, A.S. (1990) J. Exp. Med. 172, 1741-1748.
176
177,
May
31, 1991
No.
1, 1991
BIOCHEMICAL
BIOPHYSICAL
RESEARCH
COMMUNICATIONS Pages
ENDOTHELIN-1
tNDUCES AORTIC Janos
Departments University Received
AND
March
PROSTACYCLIN ENDOTHELIAL
RELEASE CELLS
FROM
G. Filep l*, Bruno Battistini I, Yvan P. C&e Adrien R. Beaudoin * and Pierre Sirois 1
of 1 Pharmacology and * Biology, of Sherbrooke, Sherbrooke, P.Q., 27,
Faculty Canada
171-176
BOVINE
*,
of Medicine, JlH 5N4
1991
SUMMARY: The effects of endothelin-1 (ET-l) on the release of prostacyclin from cultured bovine aortic endothelial cells were studied. ET-l induced a timeand dose-dependent release of 6-keto PGF,,, the stable metabolite of prostacyclin, with an apparent EC,, value of 3.0 kO.9 nM (n=6). ET-l up to a concentration of 500 nM did not affect cellular integrity. Preincubation of the cells for 30 min with 10 FM indomethacin inhibited ET-l (100 nM) - induced prostacyclin release by 90 % . These findings indicate that ET-l can directly stimulate prostacyclin release from endothelial cells probably through a receptor mediated mechanism. 0 1991Academic Press.Inc.
Endothelin-1 vascular
(ET-l)
endothelial
first isolated from conditioned
cells (1) is now well characterized
medium of cultured
as a potent constrictor
of vascular
and non-vascular
smooth muscles both in vivo and in vitro (c.f. 2).
In addition
to its contractile
action,
aggregation
ET-l
has been shown to inhibit ex vivo
of rabbit platelets (3) as well as in vivo platelet aggregation
in the
dog (4) and rabbit (5), whereas it has no effect on in vitro platelet aggregation (3,4). ET-l,
Since indomethacin the
involvement
presumably
prostacyclin,
supported
of
an
antiaggregatory
cyclooxygenase
has been suggested
(3,4).
This
by the findings that the in vivo anti aggregatory
dog was accompanied hydrolytic
and aspirin can block the antiaggregatory
metabolite
by enhanced
plasma
of prostacyclin
levels
(4). The
* To whom correspondence
product, is further
action of ET-l in the of 6-keto
present
designed to study the effects of ET-l on prostacyclin
view
action of
PGF,,,
experiments
the were
release from monolayer
should be addressed. 0006-291X/91 171
$1.50
Copyight 0 1991 by Academic Press, Inc. AlI rights of reproduction in any form reserved.
Vol.
177,.
No.
of cultured thrombin,
1, 1991
BIOCHEMICAL
endothelial a potent
cells
stimulus
AND
BIOPHYSICAL
and to compare of prostacyclin
MATERIALS
RESEARCH
the effects synthesis
COMMUNICATIONS
of ET-l
to those
of
(6).
AND METHODS
-and
chemicals. Synthetic endothelin-1 (ET-i, Peninsula Labs, Belmont, CA) was dissolved in distilled water and further diluted in 0.15 M NaCl. Thrombin (Thrombostat) was purchased from Parke Davis, Scarborough, Cnt. lndomethacin (Merck Frosst, Montreal, Canada) was dissolved in ethanol and diluted with 0.15 M NaCI. The final concentration of ethanol in the culture medium was 0.5 %. Medium 199 and lactate dehydrogenase kit were purchased from Sigma Chemical Co., St. Louis, MO; fetal calf serum from Gibco, Grand Island, N.Y. and 6-keto PGF,, antiserum from Cayman Labs, Ann Arbor, MI.
Endothelial cell culture. Bovine aortic endothelial cells were obtained from collagenase-treated (300 U/ml for 15 min at 37°C) bovine aortae (9), seeded in T 75 culture flasks (Falcon) and grown in Medium 199 supplemented with 15 % fetal calf serum (heat inactivated at 56°C for 30 min), L-glutamine 2 mM, penicillin 100 U/ml, streptomycin 0.1 mg/ml and fungizone 2.5 pg/ml. After achieving confluence, the cells were detached by using EDTA/trypsin treatment (0.4 mnn / 0.04 % in HBSS without Ca*+ and Mg*+) for 3 min at 37”C, and were subcultured for up to four times. The cells were finally seeded in 6-well plates (Falcon) with the same medium. The identity of endothelial cells grown in this fashion was verified by morphology and by demonstration of angiotensin-converting enzyme activity. The viability of cells was greater than 95 % as assessed by trypan blue exclusion. Experimental protocols. When the cells reached confluence, the culture medium was replaced 8 h before the experiments. Cells were incubated for the indicated time period with ET-l (0.1-500 nM), thrombin (0.01-0.1 U/ml) or their vehicle.. ET-l concentrations higher than 500 nM were not studied because of the limi,ted availability of the peptide. In the experiments with indomethacin, the endothelial cells were preincubated for 30 min with 10 FM indomethacin before challenge with 100 nM ET-l. Only one concentration of agonists was added to each well. At the end of the incubation period, aliquots of the medium were removed to determine concentrations of 6-keto PGF,,, the stable metabolite of prostacyclin and lactate dehydrogenase activity, respectively. The samples for 6-keto PGF,, were stored at - 20°C until assayed. Lactate dehydrogenase activity was measured on the day of the experiments using a commercial kit. Concentrations of 6-keto PGF,, were Measurement of 6- keto PGF,,. measured by a direct enzyme immunoassay according to the method of Pradelles et al.(8) . The detection limit of the assay was 0.3 pg/tube. lntrassay and interassay coefficients of variation were 5.6 % (n=5) and 9.4 % (n=4), antiserum cross-reacted with PGF, 12 %, respectively. The 6-keto PGF,, 6,15-diketo PGF,, 8 % and TXB, 0.2 %. Prostacyclin production was calculated as the difference between the amount of 6-keto PGF,, released by cells challenged with the agonist minus the amount released by identically treated but unchallenged cells. 172
Vol.
177,
No.
BIOCHEMICAL
1, 1991
AND
BIOPHYSICAL
RESEARCH
COMMUNICATIONS
Statistical analvsis. Values are reported as means +SEM. Statistical analysis of the data was performed by Dunn multiple contrast hypothesis test (9) or by Mann-Whitney U test. A p < 0.05 level was considered significant for all tests. RESULTS EndothelinInitial prostacyclin (Fig.1).
l-induced studies from
cultured
with
thrombin
be equivalent
effect
was
in prostacyclin (Fig.1).
that
bovine
prostacyclin
and the maximal
release
demonstrated
Enhanced
of changes
prostacyclin
endothelial
production reached release
to that of 0.03-0.04
was observed
was
U/ml
is capable
of releasing
cells in a time-dependent
within
The stimulatory
Thrombin,
100 nM ET-1
at 1 min of incubation,
15 min (Fig.?). observed
effect
when
manner
Similar cells
of 100 nM ET-l
time course
were was
stimulated
calculated
to
of thrombin.
0.1 U/ml
I
1 ET-l,
1 Thrombin, I
100
nM
P
E 3
0.01 U /ml
4
i
cmi;p 5o 6o 01 O ‘O 2oT?e
0
2
0 ”
10
9
ET-1 [
Log M ]
8
7
Fia. 1. Time course of 6-keto PGF,, release from cultured bovine aortic endothelial cells by endothelin-I (ET-l) and thrombin. Cells were seeded in 6-well plates, incubated in 1.9 ml of incubation medium and were stimulated with ET-1 (100 nM) or thrombin (0.01 and 0.1 U/ml). At the indicated times an aliquot was removed for determination of 6-keto PGF,, concentration.
Values
were calculated as the difference between 6-keto PGF,, levels in the medium of stimulated cells minus that of identically treated but unstimulated cells. Values are means r SEM of 3-6 separate experiments in triplicate. Fig. 2. Effect of endothelin-7 (ET-j) on 6-keto PGF,, production and lactate dehydrogenase (LDH) release by cultured bovine aortic endothelial cells. The culture and experimental conditions were identical to those described in the legend to Fig.1. Cells were stimulated with various concentrations of ET-1 for 15 min, then aliquots of the medium were removed for determination of 6-keto PGF,, concentration and LDH activity. The 6-keto PGF Icr production was calculated as the difference between the amount released by stimulated cells minus that of identically treated but unstimulated cells. Values are means + SEM of 6 separate experiments in triplicate. x, p < 0.05; xx, p < 0.01 (compared to control by Dunn multiple contrast hypothesis test). 173
6
Vol.
177,
No.
1, 1991
When
BIOCHEMICAL
cells were
a dose-dependent
exposed
increase
concentration
as low
levels
ET-l
up to a concentration
release
(Fig.2).
from
Inhibition release
was
induced
induced
EC,,
prostacyclin
set of experiments,
prostacyclin
in
released
release
absence
observed
of ET-l, (Fig.2).
increase
was
At a
in 6keto
3.0 20.9 nM (n=6).
lactate
dehydrogenase
by indomethacin
of 100 nM ET-l
and
presence
on prostacyclin
of
indomethacin.
10 PM indomethacin
on average
inhibited
lactate
n=4,
p < 0.05).
dehydrogenase
ET-l
-
by 90 % (520 ? 82 and 49 + 20 pg
by 250 000 cells per 15 min in the absence
respectively,
affected
was
significant
the effect
the
formation
of indomethacin,
concentrations
value for ET-l
of the cells for 30 min with
PGF,,
vehicle
ET-l
release
COMMUNICATIONS
(Fig.2).
compared
Preincubation
RESEARCH
of 500 nM did not affect
of ET- l- induced
In another
6-keto
in prostacyclin
The apparent
the cells
BIOPHYSICAL
for 15 min to increasing
as 1 nM,
PGF,,
AND
Neither
release
(data
and presence
indomethacin
nor its
not shown).
DISCUSSION The
present
study
dose-dependent
release
metabolite,
6-keto
Significant
prostacyclin
l-10
nM.
These
vivo platelet course
PGF,,,
must not
dehydrogenase
cellular
release,
completely
blocked
enhanced
prostacyclin of ET-l
interaction specific
on the specific further
support
ET-l
that
receptor binding
as
and
antagonists of ET-l
cells,
its putative presently to brain
to this view. 174
to inhibit (4).
Similarly
without for
addition
lactate nearly that
to a non-specific
it was
a consequence
membrane
receptors.
capillary
that ET-
indicate
are not available, endothelial
of
prostacyclin
unchanged
release
in
The time
that indomethacin
be attributed rather
cells.
acid. The findings
prostacyclin
cannot
release
by
stable
as low as
reported
the substrate
evidenced
and
endothelial
production
with the observation
- induced
ET-l
major
to that of thrombin.
arachidonic
viability,
formation
aortic
to those
was similar
indicating
coupled
time-,
by its
prostacyclin
prostacyclin
on endothelial
between ET-l
by ET-l
acid,
induce
detected at ET-l concentrations
have been endogenous
affect
bovine
or to induce
stimulated
arachidonic
synthesis 1 did
release
can
as measured
are comparable
(3-5)
ET-l
ET-l
cultured
was
concentrations
(6),
exogenous
from
release
of prostacyclin
that
of prostacyclin,
aggregation
to thrombin
action
demonstrates
the lytic
of the Although
recent cells
reports (10)
lend
Vol.
177,
No.
1, 1991
The which
BIOCHEMICAL
present
experiments
ET-l
can stimulate
can activate
phospholipase
prostacyclin
release
(4).
Stimulation
glomerular ET-l whether
ET-l
might
independent
synthesis.
A, came
with
ET-l
from
Indirect
administration
phospholipase Ca*+
concentration
phospholipase
mechanisms
reported
(11,12)
and in vivo
muscle
(13,14)
Presently
and
by adding
it is not known
via a G protein It is also
A, and C in endothelial
as it was
a sustained
demonstrated
(16).
by
that ET-l
reporting
smooth
acid.
A, directly
evidence
in vitro
A, in cultured
COMMUNICATIONS
on the mechanisms
experiments
[3H]-arachidonic
intracellular activate
RESEARCH
cells (15) has been subsequently
activates
by increasing
BIOPHYSICAL
little information
prostacyclin
of phospholipase
labeled
ET-l
give
following
mesangial
to cells
AND
or indirectly possible
that
cells by parallel
for vascular
smooth
muscle
but cells
(14). In summary, capable
of releasing
that ET-l
released
on the same mediate
the present
either
cells
and/or
prostacyclin
findings
provide
direct
from endothelial
cells.
by endothelial
and can induce
modulate
or other prostacyclin
its biological
actions,
evidence Thus,
blood-borne release, including
that
ET-l
is
one may assume cells (17) may act
which
in turn,
may
inhibition
of platelet
Research
Council
aggregation. ACKNOWLEDGMENTS: Canada
for financial
assistance. and Scientist
The authors support
and Ms.
JGF and PS are in receipt Award,
thank
the Medical
Solange
of a Medical
Cloutier Research
for expert Council
of
technical Fellowship
respectively. REFERENCES
1. 2. 3. 4. 5. 6. 7.
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