IOVS, April 1999, Vol. 40, No. 5
fined within active muscles to changes measured at the corneal
surface.
References
1. Kiuchi Y, Mishima HK, Hotehama Y, Furumoto A, Hirota A, Onari
K. Exercise intensity determines the magnitude of IOP decrease
after running. Jpn J Ophthalmol. 1994;38:191-195.
2. Harris A, Malinovsky V, Martin B. Correlates of acute exerciseinduced ocular hypotension. Invest Ophthalmol Vis Sci. 1994;35:
3852-3857.
3. Feitl ME, Krupin T. Hyperosmotic agents. In: Ritch R, Shields MB,
Krupin T, eds. The Glaucomas. St. Louis: Mosby-Year Book; 1996:
1483-1488.
4. Thomas LA, Brown SA. Relationship between colloid osmotic pressure and plasma protein concentration in cattle, horses, dogs, and
cats. AmJ Vet Res. 1992;53:224l-2244.
Effect of Ox-LDL on
Endothelium-Dependent
Response in Pig Ciliary Artery:
Prevention by an ETA Antagonist
Petit Zhu,1 Eike S. Dettmann,1
Th&rese J. Resink,2 Thomas F. Liiscber,3
Josef Flammer,1 and Ivan O. Haefliger1
investigate whether oxidized low-density lipoprotein (Ox-LDL) affects endothelium-dependent responses in isolated porcine ciliary arteries.
PURPOSE. TO
In a myograph system for isometric force measurements, quiescent vessels were incubated with 50 \i%l
ml, 100 jag/ml, or 200 jug/ml Ox-LDL; 100 jug/ml native
LDL (n-LDL); 1 jaM of the ETA- endothelin receptor antagonist BQ 123; 100 /zg/ml Ox-LDL coadministered with 1
[iM BQ 123; or 100 /xg/ml Ox-LDL coadministered with 50
\JM of the protein synthesis inhibitor cycloheximide. Vessels with nonfunctional endothelium (intentionally and
mechanically damaged) were also exposed to 100 /xg/ml
Ox-LDL. Two hours later, vessels were washed, precontracted with the thromboxane A2 analog U 46619 0*0.1
/xM), and exposed to bradykinin (0.1 nM to 3 JLIM), an
endothelium-dependent relaxing agent.
METHODS.
From the 'Laboratory of Ocular Pharmacology and Physiology,
University Eye Clinic; the department of Research, University Hospital
Basel; and the 3Laboratory of Cardiovascular Research, University Hospital Zurich, Switzerland.
Supported by Grants 32-42564.94 and 32-52783.97 from the Swiss
National Science Foundation, Bern, Switzerland; the Velux Foundation,
Zurich; and the Schwickert Foundation, Basel, Switzerland.
Submitted for publication July 7, 1998; revised November 30,
1998; accepted December 21, 1998.
Proprietary interest category: N.
Reprint requests: Ivan O. Haefliger, Laboratory of Ocular Pharmacology and Physiology, University Eye Clinic Basel, Mittlere Strasse 91,
PO Box, CH-4012 Basel, Switzerland.
Reports
1015
5. Snedecor GW, Cochran WG. Statistical Methods. 7th ed. Ames, IA:
Iowa State Univ Press; 1980:63.
6. Harris A, Malinovsky V, Cantor LB, Henderson PA, Martin BJ.
Isocapnia blocks exercise-induced reductions in ocular tension.
Invest Ophthalmol Vis Sci. 1992;33:2229-2232.
7. Mohsenin V, Gonzalez RR. Tissue pressure and plasma oncotic
pressure during exercise. / Appl Physiol. 1984;56:102-108.
8. Krupin T, Civan MM. Physiologic basis of aqueous humor formation. In: Ritch R, Shields MB, Krupin T, eds. The Glaucomas. St.
Louis: Mosby-Year Book; 1996:251-280.
9. Podos SM, Krupin T, Becker B. Effect of small dose hyperosmotic
injections on intraocular pressure of small animals and man when
optic nerves are transected and intact. Am J Ophthalmol. 1971;
71:898-905.
10. Bill A. A method to determine osmotically effective albumin and
gammaglobulin concentration in tissue fluids, its application to the
uvea and a note on the effects of capillary "leaks" on tissue fluid
dynamics. Acta Physiol Scand. 1968;73:511-522.
In quiescent vessels, Ox-LDL evoked delayed contractions. In contrast, no contractions were observed after
exposure to n-LDL, BQ 123, Ox-LDL with BQ 123, or
Ox-LDL with cycloheximide. In vessels with nonfunctional endothelium, Ox-LDL did not evoke contraction.
Bradykinin-induced relaxations were inhibited in a dosedependent manner by Ox-LDL, but not by n-LDL, BQ 123
alone, Ox-LDL with BQ 123, or Ox-LDL with cycloheximide.
RESULTS.
CONCLUSIONS. In porcine ciliary arteries, Ox-LDL affects
endothelium-dependent responses through the activation
of ETA-endothelin receptors. As Ox-LDL can accumulate
in atherosclerotic plaques, such a mechanism might be
involved in the occlusion of the ophthalmic circulation
observed in patients with hypercholesterolemia and
atherosclerosis. (Invest Ophthalmol Vis Sci. 1999;40:
1015-1020)
y virtue of its anatomic location between vascular smooth
B
muscle cells and circulating blood, the vascular endothelium is a primary target for cardiovascular risk factors, such as
low-density lipoproteins (LDLs).' During atherogenesis, plasma
LDLs undergo oxidative modification, and the oxidized-LDL
(Ox-LDL) thus generated can accumulate in constituent vessel
cells, including endothelial cells and smooth muscle cells. The
excessive uptake of cholesterol promotes subsequent formation of "foam cells," which is accompanied by loss of normal
cell function.2"4
A major function of the endothelium is to regulate vascular tone by releasing different relaxing or contracting factors,
such as nitric oxide or endothelin, respectively.5'6 Although
the endothelium appears to remain intact in early stages of
atherogenesis, pronounced endothelial dysfunction is recognized to occur.7"10 There have been some reports stating that
Ox-LDL, by interfering with the L-arginine pathway, decreases
the endothelial release of nitric oxide" and that in patients
with hypercholesterolemia, endothelium-dependent relaxations are improved by lipid-lowering therapy.12'13 It has also
been reported that in endothelial cells Ox-LDL can stimulate
the production of endothelin-114 and that patients with hyper-
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1016
Reports
lipidemia and atherosclerosis tend to have increased plasma
levels of endothelin-1.15
Although hypercholesterolemia and atherosclerosis are
known to play a major role in many ocular vascular diseases,
their respective influence on the endothelium-dependent regulation of the ophthalmic circulation has never been assessed.
Therefore, in the present study we investigated the effect of
Ox-LDL on endothelium-dependent responses of isolated porcine ciliary artery.
IOVS, April 1999, Vol. 40, No. 5
for 48 hours at 37°C. Samples were then exhaustively dialyzed
against PBS, concentrated up to 2 mg/ml to 4 mg/ml, and
stored in sterile aliquots. Complete lipid peroxidation was
confirmed by enhanced mobility of Ox-LDL (versus n-LDL)
after native gel electrophoresis in agarose.
Experimental Protocols
In accordance with the ARVO Statement for the Use of Animals
in Ophthalmic and Vision Research, eyes from farm pigs (100 125 kg; 5-6 months of age) were obtained from an abattoir
immediately after death and were maintained in cold (4°C)
modified Krebs-Ringer bicarbonate solution containing 118.6
mM NaCl, 4.7 mM KC1, 2.5 mM CaCl2, 1.2 mM MgSO4) 1.2 mM
KH2PO4, 257 mM NaHCO3, 0.026 mM EDTA, and 11.1 mM
glucose. Under a microscope (model M38; Wild, Heerbrugg,
Switzerland) the two main branches arising from the common
ophthalmic artery, the ciliary arteries, were dissected free
(diameter, 200-400 jam) and were cut into segments (~2
mm).16'17 Two tungsten wires (30 jam and 80 jam) were passed
through the lumen and attached to a force transducer (Showa
Sokki LB-5; Rikadenki, Freiburg, Germany) for measurement of
isometric forces.18
Quiescent vessels with functional endothelium were first incubated for 2 hours with Krebs-Ringer solution (control); 50
jag/ml Ox-LDL; 100 /xg/ml Ox-LDL; 200 jag/ml Ox-LDL; 100
)ag/ml n-LDL; 10~6 M of the ETA-endothelin receptor antagonist BQ 123; 100 jag/ml Ox-LDL coadministered with 10~6 M
BQ 123; or 100 jag/ml Ox-LDL coadministered with 5 X 10~5
M cycloheximide, a protein synthesis inhibitor. After 2 hours of
incubation, vessels were washed several times with KrebsRinger solution and precontracted with 10~7 M of the thromboxane A2 analog U 46619. Because contractions evoked by U
46619 tended to be slightly increased in the presence of OxLDL, the concentration of U 46619 was adapted (3 X 10~8 M
to 10~7 M) in such a way that an equivalent level of precontraction (~70% of 100 mM KC1 contractions) was reached in all
vessels. Thereafter, in a cumulative manner, the relaxing effect
of 10~10 M to 3 X 10~6 M bradykinin was assessed. A similar
experimental protocol was also conducted with 100 /xg/ml
Ox-LDL in vessels in which the endothelium had been intentionally damaged (designated as vessels with nonfunctional
endothelium). When the protein synthesis inhibitor cycloheximide was used, vessels were preincubated for 1 hour with this
drug before Ox-LDL was added.
Assessment of Endothelial Function
Drugs and Statistical Analysis
Mounted vessels were immersed in organ chambers filled with
Krebs-Ringer bicarbonate solution (37°C; 95% O2; 5% CO2;
and 10~5 M indomethacin, a cyclooxygenase inhibitor). Vessels were stretched in a 100-mg stepwise manner until their
optimal passive tension was reached. The optimal passive tension was defined as the level of vascular wall tension for which
contractions to 100 mM potassium chloride became maximal
(1025 ± 48 mg).l7 Endothelial functional integrity was assessed by adding bradykinin (10~7 M) subsequent to a contraction elicited by the thromboxane A2 analog U 46619 (10~7 M).
Endothelial function was considered to be preserved if bradykinin evoked more than 80% relaxation.'9 In a few vessels the
integrity of the endothelium was intentionally compromised by
rubbing the luminal surface with a human scalp hair. In these
vessels, bradykinin (10~7 M) evoked no response.20
Bradykinin, indomethacin, cycloheximide, and U 46619 were
purchased from Sigma (Buchs, Switzerland), BQ 123 from
MATERIALS AND METHODS
Preparation of Vessels
B
o
o
30 minutes
Functional
Endothelium
Preparation of LDLs
LDLs were isolated from blood of volunteers using sequential
buoyant-density centrifugation techniques, with potassium
bromide solutions used for density adjustments. The isolated
LDLs were exhaustively dialyzed against 0.15 M NaCl in the
presence of EDTA and butylated hydroxy toluene and were
then sterilized byfiltration(pore size: 0.45 mm; Gelman, Ann
Arbor, MI).21 Protein concentration was determined by the
Lowry method with bovine serum albumin as a standard. The
LDL samples were stored at 4°C and used within 4 weeks.
Samples prepared under these conditions are referred to as
native LDL (n-LDL).22 For oxidation, LDLs were first exhaustively dialyzed against phosphate-buffered saline (PBS) to remove EDTA and butylated hydroxy toluene, then incubated (at
a concentration of 200 mg/ml) in the presence of 5 mM CuSO4
Non-Functional
Endothelium
t
Ox-LDL 100 jig/ml
FIGURE 1. Original tracings of the effect of Ox-LDL on the tone of
quiescent porcine ciliary arteries. After approximately 1 hour of incubation with Ox-LDL (100 /xg/ml), contractions were observed in the
vessel with a functional endothelium but not in the one in which the
endothelium had been intentionally and mechanically removed (nonfunctional)-
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IOVS, April 1999, Vol. 40, No. 5
Reports
1017
30 n
eo
20©
o
I 10
a
o
n=7
""8
a
a
o -10
U
Control
J
Ox-LDL
(100 ug/ml)
Ox-LDL
(100 ug/ml)
BQ 123
(1 uM)
Ox-LDL
(100 ug/ml)
Non-Functional
Endothelium
n-LDL
(100 ug/ml)
BQ123
Ox-LDL
(100 ug/ml)
Cycloheximide
(50 uM)
FIGURE 2. Endothelium-dependent contractions elicited by Ox-LDL in isolated quiescent porcine ciliary
arteries. Incubation with Ox-LDL evoked changes in vascular tone that were significantly different from
those observed in vessels incubated with Krebs-Ringer solution (control), n-LDL, the ETA- endothelin
receptor antagonist BQ 123, Ox-LDL coadministered with BQ 123, Ox-LDL coadministered with the
protein synthesis inhibitor cycloheximide, or Ox-LDL incubated in vessels with a nonfunctional endothelium (intentionally and mechanically damaged). One-way Kruskal-Wallis test (P = 0.0003), followed by
Mann-Whitney test with Bonferroni correction: *P < 0.05; **P < 0.01.
Alexis (Laufelfingen, Switzerland), and endothelin-1 from
Bachem Feinchemikalien (Bubendorf, Switzerland). Endothelin-1 was dissolved in 0.1% bovine serum albumin, indomethacin in 10~5 M Na2CO3, and all other drugs in distilled water.
Concentrations are expressed as final molar organ-chamber
concentrations. Relaxations are shown as a percentage of the
contractions elicited by 10~7 M U 46619 and contractions as a
percentage of contractions elicited by 100 raM KC1. For each
concentration-response curve, the maximal response and the
area under the concentration-response curve were calculated.
The concentration causing 50% of the maximal response
(EC50) was expressed as a negative log M concentration (pD2).
Results are expressed as means ± SEM, and n equals the
number of animals studied (one eye per animal). One-way
analysis of variance (ANOVA), Kruskal-Wallis (nonparametric)
followed by the Mann-Whitney test with Bonferroni correction or one-way ANOVA with Scheffe's F test was used for
statistical comparison. A two-tailed P < 0.05 was considered to
be statistically significant.
RESULTS
Endothelium-Dependent Ox-LDL—Induced
Contractions
Subsequent to approximately 1 hour of incubation with 100
/Ltg/ml Ox-LDL, contractions were observed only in arteries (10
of 14 vessels studied) in which the endothelium was functional, but not in those in which the endothelium had been
intentionally damaged (Fig. 1). Thus, these results strongly
TABLE 1. Effect of Ox-LDL and n-LDL on Bradykinin-Induced Relaxations
Maximal Relaxation (%)
Control (n = 7)
50 /ag/ml Ox-LDL (n = 7)
100 /xg/ml Ox-LDL (n = 14)
200 /ug/ml Ox-LDL (n = 6)
100 jag/ml n-LDL (n = 7)
ANOVA (P value)
91 ± 5
62 ± 3*
42 ± 3***ttt
33 ± 5***ttt*
84 ± 9
< 0.0001
pD2 (-log M)
7.83
7.77
7.68
7.19
7.58
± 0.08
± 0.05
± 0.13
±0.33
± 0.26
Area under the Curve
(Relative Units)
256 ± 19
318 ± 11
361 ± 10**tt
396 ± ll***ftt
261 ± 32
< 0.0001
Mean ± SEM. ANOVA followed by Scheffe's F test. Results versus control, * P < 0.05, " P < 0.01, *** P < 0.001; versus 100 jug/ml n-LDL, t t
< 0.01, f t t P < 0.001; versus 50 /xg/ml Ox-LDL, % P < 0.05.
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1018
IOVS, April 1999, Vol. 40, No. 5
Reports
indicate that in quiescent vessels, delayed contractions evoked
by Ox-LDL were endothelium dependent.
o•
Effect of BQ 123 and Cyclohexamide on Ox-LDLInduced Contractions
20 "
In contrast to the effect observed with Ox-LDL (100 jag/ml), no
contractions occurred in vessels incubated with n-LDL (100
jag/ml), BQ 123 (10~6 M), or Krebs-Ringer solution alone
(control). Furthermore, the endothelium-dependent contractions induced by Ox-LDL (100 /xg/nil) were not observed in the
presence of the ETA-receptor antagonist BQ 123 (10~6 M), or
in the presence of the protein synthesis inhibitor cycloheximide (5 X 10~5 M). These observations indicate that the
endothelium-dependent contractions evoked by Ox-LDL were
mediated by a process involving protein synthesis and activation of an ETA-endothelin receptor (Fig. 2).
40 "
•
80 • •
Effect of BQ 123 and Cyclohexamide on the
Inhibition of Bradykinin-Evoked Relaxation by
Ox-LDL
The presence of the ETA endothelin receptor antagonist BQ
123 (10~6 M), or the protein synthesis inhibitor cycloheximide
(5 X10~5 M), prevented the inhibitory effect of Ox-LDL (100
jag/ml) on bradykinin-induced ( 1 0 ~ ' ° M t o 3 X 10~6M) endothelium-dependent relaxations (Table 2; Fig. 3, bottom).
Thus, these results indicate that Ox-LDL blunts the relaxing
effect of bradykinin by a process involving protein synthesis
and activation of an ETA- endothelin receptor.
DISCUSSION
The present study shows that in the porcine ciliary artery, by
a mechanism linked to the activation of ETA- endothelin receptors, exposure to Ox-LDL evoked endothelium-dependent contractions and inhibition of endothelium-dependent relaxations
induced by bradykinin.
The spontaneous contractions observed after approximately 1 hour of exposure to Ox-LDL (but not to n-LDL) were
elicited only in vessels with a functional endothelium (Fig. 1).
In addition, Ox-LDL-induced contractions were prevented by
the presence of the ETA-endothelin receptor antagonist BQ
123 or the protein synthesis inhibitor cycloheximide (Fig. 2).
Endothelin-1 is a potent vasoconstrictive peptide that can
be synthesized by the vascular endothelium.6 Endothelin-1 acts
through specific receptors, and activation by endothelin-1 of
ETA-endothelin receptors on vascular smooth muscle cells
evokes contractions.25 The drug BQ 123 is a potent and selec-
Ox-LDL 50 ng/ml (n = 7)
Ox-LDL 100 ng/ml (n = 14)
A Ox-LDL 200 ng/ml (n = 6)
100
10
Effect of Ox-LDL on Endothelium-Dependent
Bradykinin-Induced Relaxations
In porcine ciliary arteries, bradykinin is known to induce endothelium-dependent relaxations.23'24 In vessels precontracted
with the thromboxane A2 analog U 46619 O^IO"7 M), the
relaxation evoked by bradykinin (10~ l0 M to 3 X 10~6 M) was
significantly inhibited by Ox-LDL (50 jug/ml, 100 jug/ml, and
200 /Ltg/ml) in a concentration-dependent manner. In contrast,
n-LDL (100 /xg/ml) had no significant effect on relaxations
induced by bradykinin (Table 1; Fig. 3, top). Thus, these results
show that endothelium-dependent relaxations evoked by bradykinin were blunted by Ox-LDL.
• Control (n = 7)
O n-LDL100ng/ml(n =
60
7
6
Bradykinin (-log M)
01
if
I1
ci **
o
o
•x
c
a
x o
'S
°
o
U
20
40 •
60 "
80
•
Control (n = 7)
•
Ox-LDL 100 |ig/ml (n = 14)
O BQ 123 1 nM (n = 7)
100
J
A Ox-LDL 100 |ig/ml + BQ 123 1 (iM (n = 9)
•
Ox-LDL 100 ng/ml + Cycloheximide 50 \iM (n = 6)
10
7
6
Bradykinin (-log M)
FIGURE 3. Top: effect of Ox-LDL and n-LDL on endothelium-dependent relaxations evoked by bradykinin in porcine ciliary arteries. The
relaxations evoked by bradykinin were significantly inhibited by OxLDL (P < 0.001) in a dose-dependent manner, but not by n-LDL.
Bottom: influence of the ETA-endothelin receptor antagonist BQ 123
on the effect of Ox-LDL on bradykinin-induced relaxations. The relaxations evoked by bradykinin were significantly inhibited by Ox-LDL.
This effect was prevented by the ETA-endothelin receptor antagonist
BQ 123 or by the protein-synthesis inhibitor cycloheximide.
tive ETA- endothelin receptor antagonist known to antagonize
endothelin-1-induced contractions in human and porcine coronary arteries.25"27
It has been reported that Ox-LDL increases endothelin
transcription in porcine and human aortic endothelial cells
(within 2 hours and in a sustained manner).14 It has also been
shown that in the porcine coronary artery Ox-LDL has vasoconstrictive properties dependent on the presence of an intact
endothelium.28'29 Our results are consistent with these reports
and, in addition, establish a further link between them. That
the ETA-receptor antagonist BQ 123 and the protein synthesis
inhibitor cycloheximide could prevent endothelium-dependent contractions evoked by Ox-LDL is indicative of the in-
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IOVS, April 1999, Vol. 40, No. 5
Reports
1019
TABLE 2. Effect of BQ 123 and Cycloheximide on the Inhibition of Ox-LDL on Bradykinin-Induced Relaxations
pD 2 (-log M)
Area under the Curve
(Relative Units)
91 ± 5
42 ± 3**'
7.83 ± 0.08
7.68 ± 0.13
256 ± 19
361 ± 10***tt***§S§
78 ± 6
93 ± 4
7.85 ± 0.23
7.99 ± 0 . 1 1
283 ± 16
228 ± 25
92 ± 6
< 0.0001
7.93 ± 0.05
233 ± 14
< 0.0001
Maximal Relaxation (%)
Control in = 7)
100 /xg/ml Ox-LDL (n = 14)
100 jag/ml Ox-LDL + 1 JU-M
BQ 123 in = 9)
1 jaM BQ 123 in = 7)
100 jag/ml Ox-LDL + 50 /uM
cycloheximide (n = 6)
ANOVA (P value)
Values are means ± SEM. ANOVA followed by Scheffe's F test. Results versus control, * P < 0.05, *** P < 0.001; versus 100 /xg/ml Ox-LDL +
1 jwM BQ 123, t P < 0.05, t t P < 0.01, t t t P < 0.001; versus 1 juM BQ 123, * P < 0.05, tt$ P < 0.001; versus 100 /Lig/ml Ox-LDL + 50 /LLM
cycloheximide, §§ P < 0.01, §§§ P < 0.001.
volvement of ETA- endothelin receptors in the vasoconstrictive
effect of Ox-LDL.
Endothelium-dependent relaxations have also been shown
to be impaired by Ox-LDL in the rabbit aorta30 and in the pig
coronary artery.28 Furthermore, it has been reported that in
patients with hypercholesterolemia endothelium-dependent
vasodilation is reduced, an effect that can be reversed by the
pharmacologic lowering of cholesterol levels in the serum.13 In
accordance with these observations, we showed that Ox-LDL
inhibited endothelium-dependent relaxations induced by bradykinin in the porcine ciliary artery (Table 1; Fig. 3, top).
The mechanism of action by which Ox-LDL affects endothelium-dependent relaxations still remains unclear. Some investigators have presented evidence that Ox-LDL acts by decreasing nitric oxide synthase activity3' or by inactivating nitric
oxide,32 suggesting that Ox-LDL may interfere with the
L-arginine-nitric oxide pathway.7 Our present observation,
made in the porcine ciliary artery, suggests the existence of an
additional mechanism.
That either an inhibitor of protein synthesis or a specific
ETA-receptor antagonist could prevent the impairment of endothelium-dependent relaxations by Ox-LDL suggests the activation of ETA-endothelin receptors (Table 2; Fig. 3, bottom).
The existence of such a mechanism has recently been supported by a poster communication, providing evidence that
selective blockage of ETA- endothelin receptors restores endothelial function in the aorta of high-fat diet-treated ApoE
knockout (AKO) mice.33
Altogether, thesefindingshave potential clinical relevance
in ophthalmology. LDLs, which are the major carrier of cholesterol in the blood, can be oxidatively modified by the constituent blood vessel cells,2'3 and the Ox-LDL thus generated
can accumulate in early plaques and atherosclerotic lesions.4'34'35 Therefore, Ox-LDL may easily exert its vasoactive
effect within the vascular wall. Because the present report
shows that in porcine ciliary arteries Ox-LDL (through ETAendothelin-receptor activation) promoted endothelium-dependent contractions and inhibited endothelium-dependent relaxations, an accumulation of Ox-LDL within the vessel wall could
lead to local vascular hyperactivity and subsequent vaso9,10,26,36
In the ophthalmic circulation such a mechaspasm
nism may underlie the vascular occlusion observed, for example, in nonarteritic anterior ischemic optic neuropathy, a
condition for which hypercholesterolemia is known to be a
risk factor.3738 If it could be confirmed that such a mechanism
occurs, this could open the way to more specific therapies
using ETA-endothelin receptor antagonists for these vascular
afflictions.
In conclusion, we present evidence that in isolated porcine ciliary arteries, most likely through a mechanism linked to
the activation of ETA-endothelin receptors, Ox-LDL elicited
delayed endothelium-dependent contractions and inhibition of
bradykinin-induced endothelium-dependent relaxations. These
findings may bring new insights into the pathophysiology as
well, as they may open new therapeutic perspectives for acute
vascular occlusions frequently observed in the ophthalmic circulation of patients with hypercholesterolemia and atherosclerosis.
Acknowledgments
The authors thank Philip Hendrickson for his incomparable help and
support during the preparation of the manuscript, and Andreas
Schotzau for his valuable advice in the statistical interpretation of the
results.
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Increased Susceptibility to
Constant Light in nr andped
Mice with Inherited Retinal
Degenerations
Matthew M. LaVail,*3'4 Gregg M. Gorrin,13
Douglas Yasumura?3 and Michael T. Matthes13
determine whether the degenerating photoreceptors in nervous (nr/nr) and Purkinje cell degeneration (ped/ped) mutant mice are more susceptible to the
damaging effects of constant light than those in agematched normal mice.
PURPOSE. TO
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Beginning at two ages for each mutant, albino
nr/nr and ped/ped mice were placed into constant fluorescent light at an illuminance of 115 foot-candles to 130
foot-candles for a period of 1 week. Age-matched (usually
littermate) normal (+/—) mice were exposed at the same
time. The degree of photoreceptor cell loss was quantified
histologically by obtaining a mean outer nuclear layer
thickness for each animal. The light-exposed mice were
compared with age-matched mutant and normal mice that
were maintained in cyclic light.
METHODS.
RESULTS. The
homozygous mutants at each age showed a
significantly greater loss of photoreceptor cells caused by
constant light exposure than did the normal +/— mice in
the same period of light exposure. The nr/nr andped/ped
mutants lost two to three times the number of photore-
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