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Ocular hypertensive response to alkali burns in the monkey
Exp
Eye Res. (1973)
17, 449-453
Ocular Hypertensive Response to Alkali Burns in the Monkey CHRISTOPHER
8. PATERSOK
Divisiov~ of Ophthalmology, Denver,
AND ROSWELL
University
Col. 80220,
of Colorado
R. PFISTER Medical
Center,
U.S. A.
(Received 18 June 1973, Boston) Application of 20~1 2 iv-NaOH to the cornea of anesthetized monkeys caused a biphasic rise in intraocular pressure: an initial rapid increase, which quickly subsided, followed by a slower and sustained rise. The first rise is principally due to alkali-induced shrinkage of the outer coat of the eye. The second response was significantly reduced by pretreatment with the prostaglandin-inhibitor polyphloretin phosphate. This would suggest that the second response is mediated in part by prostaglandins.
1. Introduction Changesin intraocular pressure (IOP) following alkali burns of the rabbit eye have been investigated recently by Chiang, Moorman and Thomas (1971), Stein, Naidoff and Dawson (1973) and Paterson and Pfister (1973). It has been demonstrated that after app1yin.gsmall amounts of alkali. there is an initial rapid IOP peak which then subsides?followed by a second and sustained rise in IOP. Stein et al. (1973) and Paterson and Pfister (1973) presented evidence to suggestthat the initial IOP response was due to a sudden transient shrinkage of the outer coat of the eye. Paterson and Pfister (1973) further suggestedthat the secondrise was similar to that following all forms of ocular trauma and possibly mediated by prostaglandin releasewithin the eye. The second pressurerise following the alkali burn was significantly reduced by pretreatment with polyphloretin phosphate (PPP), a competitive inhibitor of prosbaglandins (Eakms, Miller and Karim, 1971). In the rabbit eye, trauma and local administration of prostaglandins induced a large, consistent and sustained rise in IOP (Eakinx. 1973). Relative insensitivity of the monkey eye to prostaglandins has been indicated by the results of two authors. Waitzman
(1968)
was unable
to demonstrate
any
IOP
response
to intracameral
prostaglandins, and Kelly and Starr (1971) found a variable response.Furthermore, Kelly and Starr (1971) were unable to inhibit the ocular hypertensive effects of prostaglandins by pretreatment with PPP injected irrtracamerally. The presen.t study was designed to investigate the responseof IOP in the primate to alkali, and examine the effects of PPP on that, response. 2. Methods and Materials Monkeys (two Pigtail, six Rhesus) were tranquilized with Sernylan (1 “g/kg, intramuscularly) and anesthetized with pentobarbitol. To avoid extraneous pressure recordings caused by intact orbicularis oculi muscles, the eyelids were excised prior to performing the manometric procedures. A similar approach was used previously in the rabbit (Paterson and Pfister, 1973). The femoral vein and artery were exposed and cannulated. Further anesthesia was administered via the vein and blood pressure was monitored from the artery using the system described below for IOP determination. &print requests to: Dr C. A. Paterson, BOX 2404. 4200 Enst Ninth Avenue, Denver, Cal. 80220, U.S.A.
151)
(‘. A. PA4’I‘EKSC)K
ANI)
le. 1:. l’FlSTEJ1
The animal was placed in H supitle position wit11 the heat1 supported. The :lnteriol chamber of each eye was cammlated with a ‘L.i-guage ueedle connectetl to a three-w;l> t’ap system by polyethylene tubing. The tap system permitted the eye to be connected to a heparinized saline reservoir and/or a pressure transdurrr (Bell and Howell no. 1-317-6109). The IOP was recorded on an Electronics for Medicine (lR4) recorder. The cannulatic~ll procedure was always done with the needle open to the reservoir. After closing the tap to the reservoir, t,he IOP established it steady-state level within 10 nlin. In three monkeys. 2( 1~1 of :! N-KaOH \vas applied to the cornea of one eye using all Eppendorf microp;pet. The contralateral eye served ‘tL J it control. IOP and blood pressure were monitored continually during alkali illstallxtion into the eye ant1 for the subsequent 4 hr. In another group of five monkeys. one eye of each monkey received a 0.1 ml subconjunctival injection of 10 94, PPP (A. B. Leo Laboratories. Mixed polymer, pH ‘7.0) while the control eye received 0.1 ml of saline. Both anterior chambers of each animal were oannulated 25 min after the subconjunctival injection. Shout 10 min after cannulation and 30 min after the subconjunctival injection of PPP, both eyes were burned simultaneously with 20 ~1 of 2 N-SaOH while blood pressure and IOP were monitored as described above.
3. Results The mean steady-state IOP in the eyes of the eight monkeys used was 15.44% 2.97 (S.D.). Prior to alkali burning the difference between left and right eyes was never more than 2 mmHg. Application of 20 yl of 2 N-NaOH to one eye of three monkeys resulted in a biphasic responsein IOP (Fig. 1). Th e mean initial rise in IOP was 19.6 mmHg, occurring at 0%2*0 min. The mean maximum of the second rise was 7.8 mmHg occurring at 80 min. In each of the three monkeys a marked consensualresponsewas observed in the control eye. When both eyes of a monkey were burned, the initial responsewas identical to that observed when only one eye was burned (Fig. 2). There was no difference between the
Time
FIG.
(mln)
1. Intraocular pressure and blood pressure changes 20 pl 2 N-NaOH to one eye, the other serving as a control. experiments. The bars represent the standard deviation.
in the monkey following application of The curve represents the mean of three
ALKALI
BCRNS
AED
IOP
451
initial response in PPP pretreated eyes. The mean initial rise in 10 eyes (from five monkeys) was 20.4 mmHg. The secondary hypertensive response following an alkali burn in both eyes (Fig. 2) was more variable than the response when only one eye was burned. In PPP treated eyes the mean maximum secondary response was 4.6 mmHg while that in the contralateral control eyes was 27.8 mmHg. When the individual pressure changes occurring in each of the five monkeys at 30 min or later were compared using the paired t test, the difference between the second response in PPP pretreated and control eyes was shown to be significant at the 95% confidence level.
PPP
Saline
pretreated
control
i C Time
(mln)
Fro. 2. Intraocular pressure and blood pressure changes in the monkey following application of 20 ~12 N-NaOH to both eyes. The experimental eye was pretreated with subconjunctival PPP and the control eye received a subconjunctival injection of saline. The CUTW represents the mean of five experiments. The bars represent the standard deviation.
During and immediately following the alkali burn procedure the blood pressure was unstable but subsequently remained relatively constant t’hroughout the remainder of the experiment (Figs 1 and 2). 4. Discussion The mean steady-state IOP (15.4 mm.Hg) in the monkeys observed in this study falls within the range of 8-22 mm.Hg reported in the literature. The biphasic response of IOP in the monkey eye following an alkali burn, and the consensual response are qualitatively similar to that observed in the rabbit (Paterson and Pfister, 1973). There is no reason to doubt that, as in the rabbit and human eye (Paterson and Pfister, 1973) the initial peak IOP response in the monkey eye is due to alkaliinduced shrinkage of the outer coat of the eye. The mean initial rise in IOP (20.2 mmHg) following application of 20 ~1 2 N-NaOH to 13 monkey eyes is less than that of 35.9 mmHg previously observed in the rabbit eye. This might be due to the
45”
t'. A. PATEKSOK
AND K. R. J'PISTER
thicker cornea and sclera in thck monkey eye and to the smaller amount, of scleral exposure to alkali. When one eye of the monkey was Innned and the ot’her eye used as a control, t tw mean maximum of the second rise in TOP in the experimentnl eye was 7.8 nunHg. about one-third of the responseobserved in the rabbit eye under similar conditions (Paterson and Pfister, 1973). If. a s we have suggested(Paterson and Pfister. 19X3). the secondary rise in IOP is mediated by prostaglandin release,the observation of a smaller responsein the monkey eye is consistem with a lesser sensitivity of the monkey IOP to prostaglandins. When both eyes of a monkey were burned with 20 $2 N-NaOH the secondary IOP responsewas reduced only in the eye receiving a subconjunctival injection of PPP. As in the rabbit eye, this would suggest an inhibition of the action of the prostaglandins released within t’he eye. Eakins, Whitelocke, Perkins, Bennett and Unger (1972) demonstrated that prostaglandms are released into the rabbit eye following experimentally-induced uveitis and we have demonstrated prostaglandin activity in t,he rabbit aqueous humor following an alkali burn (Paterson, Pfister and Eakins. unpublished). The ability of PPP to inhihit the ocular hypertensive responseto prostaglandins in the rabbit is adequately documented (Eakins and Sanner, 1972). Although the mixed polymer of PPP was used in this study, it has been demonstrated that the low molecular weight fraction of PPP, separated by gel fraction, was two to five times more potent as a prostaglandin antagonist (Bethel and Eakins, 1971). In the monkey, Kelly and Starr (1971), using a similar preparation of a mixed polymer of PPP, were unable to inhibit the ocular hypertensive effect of prostaglandins. These authors administered only a 1 mg do,seint,racamerally. In the present study, 10 mg of PPP were injected subconjunctivally. Possibly the lack of inhibition of prostaglandins noted by Kelly and Starr (1971) was due to an inadequate concentration of PPP at the appropriate receptor sites durin.g the releaseof prostaglandins within the eye. When both the eyes of a monkey were burned, the mean maximum secondresponse in the control eyes (278 mmHg rise) was considerably greater t.han the second responsewhen only one eye was burned (7.8 mmHg). Also, the responsewas more variable. Similar observations were made when hoth eyes of a rabbit were burned (Paterson and Pfister, 1973); although the secondresponsein the left and right nonpretreated eyes of the same animal were statistically similar, t.he magnitude of the responsewasgreater than that when only one eyeof a pair wasburned. The mechanism of this phenomenon is not understood. ACKNOWLEDGMEXTS
This study was supportedin part by a grant from the h’ational Society for the Prevention of Blindness,New York, N.Y. We would like to thank Elizabeth Brown and Elizabeth Paterson for technical assistance. PPP wasgenerouslysuppliedby Dr B. Hogberg of A. B. Leo, Halsingborg, Sweden. REFERENCES Bethel, R. A. and Eakins, K. E. (1971). Exp. Eye Res. 13, 83. Chiang, T. S., Moorman, L. R. and Thomas, R. P. (1971). Invest. Ophthalmol. 10, 270. Eakins, K. E. (1973). In The Prostaglandins (Ed. Ramwell, P. W.). P. 223. Plenum Press, York.
New
ALKALI
BURPU’S
AND
IOP
453
Eakins, K. E., Miller, J. D. and Karim, S. $1. AI. (1971). J. Pharmacol. Exp. Therup. 176,441. Eakins, K. E. and Sanner, J. E. (1972). In The Prostugkandins: Pr0gre.s in Research (Ed. Karim. S. M. M.). P. 263. Medical Technical Publishing Co. Oxford. Eakins, K. E., Whitelocke, R. A. F., Perkins, E. S., Bennett, A. and Unger, W. G. (1972). Wnture New Biol. 239, 248. Kelly, R. G. M. and Starr, M. S. (1971). Cnnnd. J. Ophthnlmol. 6, 205. Paterson, C. A. and Pfister, R. R. (1973). Arch. Ophthalmol. (In press). Stein, M. R., Xaidoff, 11. A. and Dawson, c1. R,. (1973). Amer. .I. Ophthalmol. 75, 99. Waitzman, M. B. (1968). In Prostaglandin SympoSi~um of the Worcester Foundation for Experimentnl Biology (Eds Ramwell, P. W. and Shaw. J. E.). P. 65. Interscience, New York.
Eye Res. (1973)
17, 449-453
Ocular Hypertensive Response to Alkali Burns in the Monkey CHRISTOPHER
8. PATERSOK
Divisiov~ of Ophthalmology, Denver,
AND ROSWELL
University
Col. 80220,
of Colorado
R. PFISTER Medical
Center,
U.S. A.
(Received 18 June 1973, Boston) Application of 20~1 2 iv-NaOH to the cornea of anesthetized monkeys caused a biphasic rise in intraocular pressure: an initial rapid increase, which quickly subsided, followed by a slower and sustained rise. The first rise is principally due to alkali-induced shrinkage of the outer coat of the eye. The second response was significantly reduced by pretreatment with the prostaglandin-inhibitor polyphloretin phosphate. This would suggest that the second response is mediated in part by prostaglandins.
1. Introduction Changesin intraocular pressure (IOP) following alkali burns of the rabbit eye have been investigated recently by Chiang, Moorman and Thomas (1971), Stein, Naidoff and Dawson (1973) and Paterson and Pfister (1973). It has been demonstrated that after app1yin.gsmall amounts of alkali. there is an initial rapid IOP peak which then subsides?followed by a second and sustained rise in IOP. Stein et al. (1973) and Paterson and Pfister (1973) presented evidence to suggestthat the initial IOP response was due to a sudden transient shrinkage of the outer coat of the eye. Paterson and Pfister (1973) further suggestedthat the secondrise was similar to that following all forms of ocular trauma and possibly mediated by prostaglandin releasewithin the eye. The second pressurerise following the alkali burn was significantly reduced by pretreatment with polyphloretin phosphate (PPP), a competitive inhibitor of prosbaglandins (Eakms, Miller and Karim, 1971). In the rabbit eye, trauma and local administration of prostaglandins induced a large, consistent and sustained rise in IOP (Eakinx. 1973). Relative insensitivity of the monkey eye to prostaglandins has been indicated by the results of two authors. Waitzman
(1968)
was unable
to demonstrate
any
IOP
response
to intracameral
prostaglandins, and Kelly and Starr (1971) found a variable response.Furthermore, Kelly and Starr (1971) were unable to inhibit the ocular hypertensive effects of prostaglandins by pretreatment with PPP injected irrtracamerally. The presen.t study was designed to investigate the responseof IOP in the primate to alkali, and examine the effects of PPP on that, response. 2. Methods and Materials Monkeys (two Pigtail, six Rhesus) were tranquilized with Sernylan (1 “g/kg, intramuscularly) and anesthetized with pentobarbitol. To avoid extraneous pressure recordings caused by intact orbicularis oculi muscles, the eyelids were excised prior to performing the manometric procedures. A similar approach was used previously in the rabbit (Paterson and Pfister, 1973). The femoral vein and artery were exposed and cannulated. Further anesthesia was administered via the vein and blood pressure was monitored from the artery using the system described below for IOP determination. &print requests to: Dr C. A. Paterson, BOX 2404. 4200 Enst Ninth Avenue, Denver, Cal. 80220, U.S.A.
151)
(‘. A. PA4’I‘EKSC)K
ANI)
le. 1:. l’FlSTEJ1
The animal was placed in H supitle position wit11 the heat1 supported. The :lnteriol chamber of each eye was cammlated with a ‘L.i-guage ueedle connectetl to a three-w;l> t’ap system by polyethylene tubing. The tap system permitted the eye to be connected to a heparinized saline reservoir and/or a pressure transdurrr (Bell and Howell no. 1-317-6109). The IOP was recorded on an Electronics for Medicine (lR4) recorder. The cannulatic~ll procedure was always done with the needle open to the reservoir. After closing the tap to the reservoir, t,he IOP established it steady-state level within 10 nlin. In three monkeys. 2( 1~1 of :! N-KaOH \vas applied to the cornea of one eye using all Eppendorf microp;pet. The contralateral eye served ‘tL J it control. IOP and blood pressure were monitored continually during alkali illstallxtion into the eye ant1 for the subsequent 4 hr. In another group of five monkeys. one eye of each monkey received a 0.1 ml subconjunctival injection of 10 94, PPP (A. B. Leo Laboratories. Mixed polymer, pH ‘7.0) while the control eye received 0.1 ml of saline. Both anterior chambers of each animal were oannulated 25 min after the subconjunctival injection. Shout 10 min after cannulation and 30 min after the subconjunctival injection of PPP, both eyes were burned simultaneously with 20 ~1 of 2 N-SaOH while blood pressure and IOP were monitored as described above.
3. Results The mean steady-state IOP in the eyes of the eight monkeys used was 15.44% 2.97 (S.D.). Prior to alkali burning the difference between left and right eyes was never more than 2 mmHg. Application of 20 yl of 2 N-NaOH to one eye of three monkeys resulted in a biphasic responsein IOP (Fig. 1). Th e mean initial rise in IOP was 19.6 mmHg, occurring at 0%2*0 min. The mean maximum of the second rise was 7.8 mmHg occurring at 80 min. In each of the three monkeys a marked consensualresponsewas observed in the control eye. When both eyes of a monkey were burned, the initial responsewas identical to that observed when only one eye was burned (Fig. 2). There was no difference between the
Time
FIG.
(mln)
1. Intraocular pressure and blood pressure changes 20 pl 2 N-NaOH to one eye, the other serving as a control. experiments. The bars represent the standard deviation.
in the monkey following application of The curve represents the mean of three
ALKALI
BCRNS
AED
IOP
451
initial response in PPP pretreated eyes. The mean initial rise in 10 eyes (from five monkeys) was 20.4 mmHg. The secondary hypertensive response following an alkali burn in both eyes (Fig. 2) was more variable than the response when only one eye was burned. In PPP treated eyes the mean maximum secondary response was 4.6 mmHg while that in the contralateral control eyes was 27.8 mmHg. When the individual pressure changes occurring in each of the five monkeys at 30 min or later were compared using the paired t test, the difference between the second response in PPP pretreated and control eyes was shown to be significant at the 95% confidence level.
PPP
Saline
pretreated
control
i C Time
(mln)
Fro. 2. Intraocular pressure and blood pressure changes in the monkey following application of 20 ~12 N-NaOH to both eyes. The experimental eye was pretreated with subconjunctival PPP and the control eye received a subconjunctival injection of saline. The CUTW represents the mean of five experiments. The bars represent the standard deviation.
During and immediately following the alkali burn procedure the blood pressure was unstable but subsequently remained relatively constant t’hroughout the remainder of the experiment (Figs 1 and 2). 4. Discussion The mean steady-state IOP (15.4 mm.Hg) in the monkeys observed in this study falls within the range of 8-22 mm.Hg reported in the literature. The biphasic response of IOP in the monkey eye following an alkali burn, and the consensual response are qualitatively similar to that observed in the rabbit (Paterson and Pfister, 1973). There is no reason to doubt that, as in the rabbit and human eye (Paterson and Pfister, 1973) the initial peak IOP response in the monkey eye is due to alkaliinduced shrinkage of the outer coat of the eye. The mean initial rise in IOP (20.2 mmHg) following application of 20 ~1 2 N-NaOH to 13 monkey eyes is less than that of 35.9 mmHg previously observed in the rabbit eye. This might be due to the
45”
t'. A. PATEKSOK
AND K. R. J'PISTER
thicker cornea and sclera in thck monkey eye and to the smaller amount, of scleral exposure to alkali. When one eye of the monkey was Innned and the ot’her eye used as a control, t tw mean maximum of the second rise in TOP in the experimentnl eye was 7.8 nunHg. about one-third of the responseobserved in the rabbit eye under similar conditions (Paterson and Pfister, 1973). If. a s we have suggested(Paterson and Pfister. 19X3). the secondary rise in IOP is mediated by prostaglandin release,the observation of a smaller responsein the monkey eye is consistem with a lesser sensitivity of the monkey IOP to prostaglandins. When both eyes of a monkey were burned with 20 $2 N-NaOH the secondary IOP responsewas reduced only in the eye receiving a subconjunctival injection of PPP. As in the rabbit eye, this would suggest an inhibition of the action of the prostaglandins released within t’he eye. Eakins, Whitelocke, Perkins, Bennett and Unger (1972) demonstrated that prostaglandms are released into the rabbit eye following experimentally-induced uveitis and we have demonstrated prostaglandin activity in t,he rabbit aqueous humor following an alkali burn (Paterson, Pfister and Eakins. unpublished). The ability of PPP to inhihit the ocular hypertensive responseto prostaglandins in the rabbit is adequately documented (Eakins and Sanner, 1972). Although the mixed polymer of PPP was used in this study, it has been demonstrated that the low molecular weight fraction of PPP, separated by gel fraction, was two to five times more potent as a prostaglandin antagonist (Bethel and Eakins, 1971). In the monkey, Kelly and Starr (1971), using a similar preparation of a mixed polymer of PPP, were unable to inhibit the ocular hypertensive effect of prostaglandins. These authors administered only a 1 mg do,seint,racamerally. In the present study, 10 mg of PPP were injected subconjunctivally. Possibly the lack of inhibition of prostaglandins noted by Kelly and Starr (1971) was due to an inadequate concentration of PPP at the appropriate receptor sites durin.g the releaseof prostaglandins within the eye. When both the eyes of a monkey were burned, the mean maximum secondresponse in the control eyes (278 mmHg rise) was considerably greater t.han the second responsewhen only one eye was burned (7.8 mmHg). Also, the responsewas more variable. Similar observations were made when hoth eyes of a rabbit were burned (Paterson and Pfister, 1973); although the secondresponsein the left and right nonpretreated eyes of the same animal were statistically similar, t.he magnitude of the responsewasgreater than that when only one eyeof a pair wasburned. The mechanism of this phenomenon is not understood. ACKNOWLEDGMEXTS
This study was supportedin part by a grant from the h’ational Society for the Prevention of Blindness,New York, N.Y. We would like to thank Elizabeth Brown and Elizabeth Paterson for technical assistance. PPP wasgenerouslysuppliedby Dr B. Hogberg of A. B. Leo, Halsingborg, Sweden. REFERENCES Bethel, R. A. and Eakins, K. E. (1971). Exp. Eye Res. 13, 83. Chiang, T. S., Moorman, L. R. and Thomas, R. P. (1971). Invest. Ophthalmol. 10, 270. Eakins, K. E. (1973). In The Prostaglandins (Ed. Ramwell, P. W.). P. 223. Plenum Press, York.
New
ALKALI
BURPU’S
AND
IOP
453
Eakins, K. E., Miller, J. D. and Karim, S. $1. AI. (1971). J. Pharmacol. Exp. Therup. 176,441. Eakins, K. E. and Sanner, J. E. (1972). In The Prostugkandins: Pr0gre.s in Research (Ed. Karim. S. M. M.). P. 263. Medical Technical Publishing Co. Oxford. Eakins, K. E., Whitelocke, R. A. F., Perkins, E. S., Bennett, A. and Unger, W. G. (1972). Wnture New Biol. 239, 248. Kelly, R. G. M. and Starr, M. S. (1971). Cnnnd. J. Ophthnlmol. 6, 205. Paterson, C. A. and Pfister, R. R. (1973). Arch. Ophthalmol. (In press). Stein, M. R., Xaidoff, 11. A. and Dawson, c1. R,. (1973). Amer. .I. Ophthalmol. 75, 99. Waitzman, M. B. (1968). In Prostaglandin SympoSi~um of the Worcester Foundation for Experimentnl Biology (Eds Ramwell, P. W. and Shaw. J. E.). P. 65. Interscience, New York.