Ocular irritative response to YAG laser capsulotomy in rabbits: release of calcitonin gene-related peptide and effects of methysergide.

The Neodymium (Nd):YAG laser is commonly used in ophthalmology mainly for the posterior capsulotomy in patients with secondary cataract after extracapsular cataract extraction. A frequent side-effect following different kinds of YAG laser treatments is an acute increase in the intraocular pressure (IOP). The present study addresses the role of calcitonin gene-related peptide (CGRP) in the ocular irritative response following YAG laser anterior capsulotomy in rabbits. The YAG laser anterior capsulotomy caused an irritative response in the eye, which consisted of an increase in the IOP, miosis and breakdown of the blood-aqueous barrier. Following YAG laser capsulotomy, CGRP-immunoreactivity was found in the aqueous humour in different molecular weight forms as revealed by gel-permeation chromatography. One of the peaks coeluted with synthetic human CGRP. Methysergide attenuated the increase in the IOP and disruption of the blood-aqueous barrier, but not the miosis, following YAG laser anterior capsulotomy. The present study demonstrates the release of CGRP into the aqueous humour following YAG laser capsulotomy, and suggests that CGRP is partly causing the increase in IOP and disruption of the blood-aqueous barrier in this irritative response.     

The intraocular pressure response of conscious rabbits to clonidine.

A study has been made of the time courses of the pupillary and intraocular pressure responses of conscious rabbits to clonidine administered either topically or intravenously. Topical unilateral application of clonidine caused transient pupil dilatation and a biphasic intraocular pressure response; an initial hypertensive response preceded a hypotensive phase lasting several hours. Pupillary and hypertensive responses were absent in the untreated eye, but there was a rapid decrease of intraocular pressure. Intravenous administration of clonidine caused an immediate and large decrease of intraocular pressure in both eyes. Phenoxybenzamine given intravenously inhibited the pupillary dilatation and the hypertensive responses to clonidine. The role of efferent adrenergic neuronal activity in mediating the local biphasic pressure response was studied in rabbits with unilateral precervical and postcervical sympathotomy. The results showed the hypotensive response to be dependent on an intact adrenergic innervation of the ocular tissues.     

The biphasic intraocular pressure response of rabbits to epinephrine.

A study has been made of the pupillary and intraocular pressure responses of conscious rabbits to daily topical applications of submaximal doses of epinephrine. On the first day, epinephrine caused rapid pupil dilation which preceded a prolonged -ecrease of intraocular pressure. On the second and subsequent days, the application of the same dose of epinephrine increased the duration of the pupillary response and caused a biphasic pressure response in all treated eyes; an initial increase of intraocular pressure lasting two to four hours followed by decrease of intraocular pressure below the initial value which lasted for more than twenty-four hours. The beta-receptor antagonist, propranolol, and the alpha-receptor antagonist, phenoxybenzamine, caused small and large reductions, respectively, in the hypertensive response to epinephrine. Phenoxybenzamine, but not propranolol, also inhibited the pupil dilation and the hypotensive response to epinephrine. Topical administration of phenoxybenzamine strongly inhibited the hypertensive response to epinephrine but left unaffected the pupillary response.     

The reproducibility of the intraocular pressure response to dexamethasone.

The reproducibility of the intraocular pressure response to topical dexamethasone was investigated in 162 persons previously classified as low (NN), intermediate (NG), or high (GG) responders. The concordance of first and second test results was 71% for NN, 74% for NG, and 79% for GG responders, exceeding chance significantly for the NG and GG categories. Quantitative assessment revealed significant correlation of final pressure achieved on first and second tests (r equals .747, P LESS THAN .001). In the course of the study applications of dexamethasone to one eye were noted to have no effect on the intraocular pressure in the contralateral untreated eye, nor did testing of one eye influence the response of the contralateral eye in simultaneous bilateral testing. Using our data to estimate the reproducibility of topical testing in a general population, a value of 73% was obtained. That value was similar to the 65% concordance reported in an identical twin study, suggesting that the limited precision of topical testing accounts for the relatively low concordance found in that study.     

The anti-inflammatory regulation of calcitonin gene-related peptide in mouse Aspergillus fumigatus keratitis

AIM: To analyze the impact of calcitonin gene-related peptide (CGRP) in mouse keratitis after Aspergillus fumigatus (A. fumigatus) infection. METHODS: C57BL/6 mice were treated subconjunctivally with different concentrations of exogenous CGRP, and BALB/c mice were treated with CGRP8-37 (a CGRP antagonist) before corneas were infected with A. fumigatus. The cornea was assessed under the slit-lamp and the clinical score was recorded. The mRNA levels of IL-1β, TNF-α, IL-6, and MIP-2 were detected by quantitative real-time polymerase chain reaction (PCR), while the protein level of IL-1β was determined by Western blotting. In vitro, RAW264.7 cells were used to investigate NLRP3 and IL-1β expression induced by A. fumigatus after the pretreatment of exogenous CGRP or CGRP8-37. Cytokines expression in RAW264.7 cells was evaluated by real-time PCR and Western blotting. RESULTS: Using exogenous CGRP resulted in down-regulated synthesis of IL-1β and MIP-2 stimulated by A. fumigatus in C57BL/6 mice keratitis, and the synthesis of IL-1β, MIP-2 and IL-6 was up-regulated in BALB/c mice corneas after the pretreatment with CGRP8-37. Pretreatment with exogenous CGRP and CGRP8-37 did not influence TNF-α mRNA levels either in BALB/c or C57BL/6 mice keratitis. The levels of NLRP3 and IL-1β were both reduced in A. fumigatus stimulated-macrophages after treatment with exogenous CGRP. And CGRP8-37 pretreatment would increase NLRP3 and IL-1β levels. CONCLUSION: CGRP may alleviate the inflammatory reaction in mice keratitis after infection with A. fumigatus. The anti-inflammatory effect may be related to the inhibition of NLRP3 expression by CGRP.     

Expression and role of calcitonin gene-related peptide in mouse Aspergillus fumigatus keratitis

AIM: To investigate the expression and role of calcitonin gene-related peptide (CGRP) in the mouse models induced by Aspergillus fumigatus (A. fumigatus). METHODS: C57BL/6 mice were randomized into a control group and A. fumigatus keratitis group. The cornea photography was assessed under the slit lamp and the clinical score was recorded after infection. Western blot, real-time polymerase chain reaction (PCR) and immunohistofluorescence analysis were applied to detect CGRP expression in cornea of both groups. In vitro, tests were conducted with C57BL/6 mice macrophages to investigate CGRP expression after interaction with A. fumigatus. Cytokines expression induced by exogenous CGRP and the antagonist CGRP8-37 in A. fumigatus-exposed macrophages was evaluated by real-time PCR and ELISA. RESULTS: The cornea expression of CGRP was significantly elevated in C57BL/6 mice corneas and macrophages after A. fumigatus infection. After treatment with exogenous CGRP, the levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and IL-6 were reduced, and IL-10 level was increased in the A. fumigatus stimulated-macrophages. However, IL-1β, TNF-α and IL-6 levels were upregulated after pretreatment of CGRP8-37. But the mRNA levels of MIP-2, TGF-β and IL-10 were not changed. CONCLUSION: This study provides evidence that A. fumigatus increased CGRP expression. CGRP may play a protective role against inflammation in A. fumigatus keratitis.     

Effects of calcitonin gene-related peptide in the eye. A study in rabbits and cats

Calcitonin gene-related peptide (CGRP) has recently been demonstrated in sensory neurons of the eye. The purpose of the present study was to determine the effects of exogenous CGRP in the rabbit and cat eye. CGRP was injected intracamerally and the intraocular pressure was measured in cannulated eyes. The pupil diameter and the aqueous humor protein concentration were also measured. Indomethacin was used to prevent prostaglandin synthesis and tetrodotoxin (TTX) to block nerve conductance. In the rabbit eye, CGRP caused iridial hyperemia, a breakdown of the blood-aqueous barrier and increased intraocular pressure. These responses were dose-related. The increase in IOP as well as the breakdown of the blood-aqueous barrier could not be blocked with TTX or indomethacin. In cats CGRP caused a decrease in IOP and had only slight effect on the aqueous humor protein concentration. Neither in rabbits nor in cats had CGRP any detectable effect on the pupil size. Intracameral injection of 0.1 microgram (7.4 x 10(-11) moles) substance P together with 0.1 microgram (2.6 x 10(-11) moles) CGRP in rabbits caused maximal miosis but did not potentiate the intraocular effects of CGRP only. These results indicate that CGRP has marked vascular effects in the rabbit eye, causing a breakdown of the blood-aqueous barrier and increased IOP. The mechanism of this phenomenon does not involve prostaglandins neither nerve conduction, implying most likely a direct effect on the vascular smooth muscle. The mechanism of the decrease of IOP in cats remains unknown.     

125I]calcitonin gene-related peptide binding in membranes of the ciliary body-iris block.

Calcitonin gene-related peptide (CGRP) is a mediator of intraocular inflammatory responses, but it may also affect aqueous humour dynamics. The aim of the present work was to characterize CGRP binding sites in the eyes of various mammals. The binding of radiolabelled human CGRP to membranes from the ciliary body-iris (c+i) block of porcine eye showed characteristics expected of an interaction with a receptor site: it was reversible, saturable and displaced by rat CGRP and calcitonin. Studies with CGRP fragments demonstrated the importance of rather long carboxy-terminal sequences of the CGRP molecule for high-affinity binding to the receptor. Rat islet amyloid polypeptide (IAPP), which has about 50% structural similarity to CGRP, displaced radioligand binding nearly as efficiently as CGRP, while human IAPP was about twenty-fold less potent. No displaceable CGRP binding could be reliably demonstrated by the present method in c+i membranes from cat, rabbit and bovine eyes, thus indicating differences in the number or localization of CGRP receptors between different mammalian species.     

Acute intraocular pressure response to argon laser iridotomy

Argon laser iridotomy (ALI) was performed in 50 eyes for prophylactic treatment of anatomically narrow iridocorneal angles and in 50 eyes for therapy of chronic angle-closure glaucoma. Intraocular pressure was increased 6 mmHg or more 1 to 2 hours after ALI in 19 of 50 eyes with anatomical narrow iridocorneal angles and in 23 of 50 eyes with chronic angle-closure glaucoma. Increases greater than 20 mmHg over baseline value occurred in 5 of 50 eyes with narrow iridocorneal angles and in 7 of 50 eyes with chronic angle-closure glaucoma. A clinically significant increase in intraocular pressure (defined as a pressure 30 mmHg or greater and 40% or more increased over the pre-laser value) occurred 1 to 2 hours after ALI in 11 of 50 eyes with narrow iridocorneal angles and in 17 of 50 eyes with chronic angle-closure glaucoma. There was no statistical difference (chi square P greater than 0.3) in the incidence of this complication in the two groups. Additional medical therapy was effective in lowering the acute laser-induced elevation in intraocular pressure. Patient diagnosis, patient demographics, preoperative glaucoma medication and laser treatment parameters did not predict which eyes would develop this complication. Eyes which did not have a clinically significant elevation in intraocular pressure 1 to 2 hours after ALI did not show a later increase at 24 hours.     

Early intraocular pressure response following laser trabeculoplasty.

The early response in the intraocular pressure following laser trabeculoplasty was investigated in 38 patients. An increase in pressure was found in 16 patients (42%), of whom eight had a moderate (less than 9 mmHg) and eight a severe (greater than 10 mmHg) increase. The maximum increase was recorded during the first post-laser hour in 13 patients (34.2%) and at 4 h in three patients postoperatively. A routine follow-up observation at 4 h after laser treatment is recommended to prevent 'silent' hypertensive risk.     

Ocular pigmentation and intraocular pressure response to forskolin

We studied the effects of a forskolin suspension on intraocular pressure (IOP) in normal albino and pigmented rabbits and in alpha-chymotrypsin induced ocular hypertensive rabbits. Experimental-induced ocular hypertensive rabbits were produced by injecting of alpha-chymotrypsin (167 units) into the posterior chamber of the eye of albino rabbits. Ocular hypertensive rabbits were classified into 3 groups according to the IOP (Group A; 15-19 mmHg, B; 20-24 mmHg, C; 25-29 mmHg). Topical application of 1% forskolin caused a significant decrease in IOP in Groups B and C, as well as in normal albino and pigmented rabbits. The hypotensive effects were lower in pigmented rabbits than in albino rabbits, although the duration was longer. Subconjunctival injection of 1% forskolin reduced IOP 1 to 5 hrs after treatment in albino rabbits. However, in pigmented rabbits, a slight increase in IOP was observed at 30 min, followed by a significant decrease 5 to 10 hrs after injection. Furthermore, the binding ability of forskolin to melanin granules was determined in vitro. Forskolin exhibited specific affinity towards melanin granules obtained from bovine eyes, with the binding reaching a plateau after 5 min of incubation.     

Immediate intraocular pressure response to selective laser trabeculoplasty

BACKGROUND/AIMS: Selective laser trabeculoplasty targets the pigmented trabecular meshwork cells without damage to the trabecular meshwork architecture in vitro. A study was conducted in vivo of eight eyes with uncontrolled open angle glaucoma to ascertain the immediate intraocular response to selective laser trabeculoplasty. METHODS: The trabecular meshwork of each eye was treated 360 degrees with a frequency doubled Q-switched Nd:YAG laser. Intraocular pressure was measured 1, 2, 24 hours and 1, 4, 6 weeks after treatment. RESULTS: The average preoperative intraocular pressure was 26.6 (SD 7) mm Hg (range 18-37). Two hours and 6 weeks respectively after selective trabeculoplasty intraocular pressure was reduced in all the eyes treated with an average fall of 10.6 (5.2) mm Hg or 39.9%. A pressure spike of 10 mm Hg verified in one eye 1 hour after treatment. CONCLUSIONS: Selective laser trabeculoplasty decreased intraocular pressure by an amount similar to that achieved with standard trabeculoplasty. Additional study is needed to determine whether the beneficial effect is sustained over a longer period of follow up.     

Biphasic intraocular pressure response to Q-switched Nd:YAG laser irradiation of the iris and the apparent mediatory role of prostaglandins

In rabbits, laser irradiation of the iris causes an immediate rise in intraocular pressure (IOP), with a concomitant increase of prostaglandins (PGs) in the aqueous humor. We studied IOP responses to Q-switched Nd:YAG laser application to the iris in unanesthetized rabbits, and found that a prolonged IOP reduction lasting for 6-24 hr invariably followed the transient IOP rise of 0.5-2 hr duration. The magnitude of both the IOP rise and reduction was dependent on the level of laser energy. A masked, randomized study revealed that the intraperitoneal administration of indomethacin (50 mg kg-1) prior to laser application significantly reduced the ocular hypertensive and hypotensive responses to laser irradiation (energy: 24 mJ). The maximum IOP rise from baseline was 5.4 +/- 3.0 mmHg (n = 10) with the intraperitoneal vehicle and 1.5 +/- 4.2 mmHg (n = 10) with intraperitoneal indomethacin administration. Thus, the difference was statistically significant (P less than 0.025, Student's t-test). The maximum IOP reduction from baseline was -8.5 +/- 2.6 mmHg (n = 10) with the intraperitoneal vehicle and -4.0 +/- 2.4 mmHg (n = 10) with intraperitoneal indomethacin (P less than 0.001, Student's t-test). The concentration of PGE2 in the aqueous humor, as determined by radioimmunoassay on samples obtained at 2 and 4 hr after laser application, was found to be significantly increased in rabbits that received the vehicle solution but not in animals that were pretreated with intraperitoneal injection of indomethacin. This suggests that this PG or other cyclooxygenase products are involved with mediation of the initial IOP increase and the prolonged decrease in IOP that follows laser irradiation of the iris.     

Postural response of intraocular pressure following traumatic hyphaema.

Twenty patients with previous unilateral traumatic hyphaema and 25 age-matched controls were studied. There was a progressive rise in intraocular pressure when the patient changed from the standing to the sitting position and then to the lying position in both groups. No control eye showed a rise greater than 2 mmHg when the subject changed from sitting to lying. However, 14 (70%) of the injured eyes and 12 (60%) of the fellow eyes showed an exaggerated response. We suggest that the presence of an abnormal postural response may indicate a predisposition to post-traumatic glaucoma. Our findings are compatible with a linked control of postural intraocular pressure response between the two eyes.     

Distinct substance P and calcitonin gene-related peptide immunoreactive nerves in the guinea pig eye

Using a double labeling indirect immunofluorescent technique, we studied the guinea pig trigeminal ganglion and eye for co-localization of substance P and calcitonin gene-related peptide. In the trigeminal ganglion, the number of neurons immunoreactive for calcitonin gene-related peptide significantly outnumber those immunoreactive for substance P, but virtually all substance P positive neurons are immunoreactive for calcitonin gene-related peptide. In the eye, a complex pattern of co-localization is present; both peptides co-localize in most immunoreactive nerve fibers. Nerve fibers immunoreactive only for calcitonin gene-related peptide tend to be concentrated in the cornea and posterior ciliary body. Nerve fibers immunoreactive only for substance P are present in relation to both iris muscles. Sensory denervation by intracranial transection of the ophthalmic and maxillary nerves fails to eliminate these substance P positive but CGRP negative iris nerve fibers. These findings indicate an alternative origin for substance P immunoreactive nerves supplying the iris muscles in this species.     

Elevated levels of calcitonin gene-related peptide in aqueous humor of patients with proliferative vitreoretinopathy

Purpose: To detect the levels of the sensory peptide calcitonin gene-related peptide in aqueous humor of patients with proliferative vitreoretinopathy and to compare them with those of uninflamed eyes (cataract and uncomplicated rhegmatogenous retinal detachment). Materials and methods: Using a highly specific and sensitive radioimmunoassay the concentration of calcitonin gene-related peptide was detected in fresh samples of aqueous humor obtained via paracentesis. Furthermore, calcitonin gene-related peptide-like immunoreactivities were characterized by high-pressure liquid chromatography. Results: The mean level of calcitonin gene-related peptide was 6.11 fmol/ml in cataract controls and 14.77 fmol/ml in uncomplicated rhegmatogenous retinal detachment. In the cataract group, 9 of 18 cases were below the detection limit and in the retinal detachment group, 5 of 16. In proliferative vitreoretinopathy, the peptide averaged 76.92 fmol/ml and none of the samples was below the detection limit. High-pressure liquid chromatography revealed one major peak corresponding to synthetic calcitonin gene-related peptide. Conclusion: In recent studies, we found elevated levels of the sensory peptide substance P in aqueous humor of patients with proliferative vitreoretinopathy. This fact and the present result, the elevation of calcitonin gene-related peptide in aqueous humor of eyes with proliferative vitreoretinopathy, clearly point to an involvement of sensory peptides in the pathobiology of the disease. The source of the elevation is not clear, but we hypothesize that it originates from a neurogenic mechanism, i.e. an acceleration of the peptides by their enhanced release from the iris/ciliary body complex subsequent to sensitization of sensory neurons, thus representing a very interesting epiphenomenon of proliferative vitreoretinopathy. Our results constitute novel aspects in the pathophysiological concept of proliferative vitreoretinopathy and extend the knowledge about the pathobiology of the disease process. Received: 14 June 1999 Revised version received: 9 August 1999 Accepted: 30 August 1999     

Intraocular and cardiovascular effects of calcitonin gene-related peptide (CGRP)-I and -II in the rabbit.

Calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide localized in the eye in the sensory nerves. In this study, the physiological effects of the two naturally occurring forms of human CGRP, CGRP-I, and -II, which differ only in three amino acids, have been demonstrated in the rabbit eye and cardiovascular system. Intravenously administered CGRP-I caused a biphasic increase in the intraocular pressure (IOP), disruption of the blood-aqueous barrier, and increase in the cyclic adenosine 3',5'-monophosphate (cAMP) content in the aqueous humor. CGRP-II caused a monophasic increase in the IOP and disruption of the blood-aqueous barrier, but no increase in the cAMP content occurred. CGRP-I and -II decreased the blood pressure in a similar dose-dependent manner. The effects of intracamerally administered CGRP-I and -II were very similar in the eye. An increase in the IOP, breakdown of the blood-aqueous barrier, and an increase in the cAMP content in the aqueous humor occurred. The differences in the biological responses between CGRP-I and -II in the rabbit eye might be a result of the different affinities of the CGRP forms to a single receptor. Alternatively, different subtypes of receptors for CGRP-I and -II may exist in the rabbit.