Quantitative autoradiography of beta-adrenergic receptors in rabbit eyes

The Multifarious Effects of Various Glaucoma Pharmacotherapy on Corneal Endothelium: A Narrative Review

Corneal endothelium is a single cell layer that is mainly responsible for maintaining corneal clarity. Endothelial damage secondary to toxicity, stress, or genetic predisposition are common and in conjunction with the low regenerative ability of the cells, making their preservation critical for maintaining visual acuity. Patients with glaucoma, who are estimated to be close to 80 million worldwide, have a plethora of reasons for developing endothelial damage, being exposed to a spectrum that extends from various medical and surgical interventions to the disease itself. The wide spectrum of glaucoma pharmacotherapy that has been recently extended by addition of newer classes of medications has been the focus of extensive research on its effects on corneal endothelium. Both basic and clinical research have attempted to shine a light on the complex mechanisms associated with the effects of glaucoma medication on corneal endothelium and to answer the important question as to whether these findings are clinically significant. The aim of this review is to summarize and present current literature of the various findings, both from in vivo and in vitro studies that have focused on the complex relationship between different classes of glaucoma medication and their effect on corneal endothelium.

Dysregulation of the autonomous nervous system in patients with temporomandibular disorder: a pupillometric study

The role of the autonomic nervous system (ANS) was recently investigated in Temporomandibular disorders (TMD). Several authors argue that in subjects with TMD there is a dysregulation of ANS. Recent literature support that Pupillometry is a simple non-invasive tool to study ANS. The aim of this study was to investigate the relationship between TMD and ANS activity using pupillometry recording in Infrared light at rest Mandible Position (RP); Infrared light at Forced Habitual Occlusion (FHO); Yellow-green light at RP; Yellow-green light at FHO. Forty female subjects were enrolled: 20 case patients showed TMD based on the Research Diagnostic Criteria for TMD, and 20 control patients, aged matched, had no signs or symptoms of TMD. Statistical analysis was performed on average pupil size. Ratio between pupil size in FHO and RP (FHO/RP ratio) and yellow-green and infrared (light/darkness ratio) lighting were carried out. Within group differences of pupil size and of “ratio” were analyzed using a paired t test, while differences of pupil size between groups were tested using an unpaired t test. Statistical comparisons between groups showed no significant differences of absolute values of pupil dimension in RP and FHO, both in yellow-green and in infrared lighting. In addition, there were no significant differences within groups comparing RP and FHO in yellow-green light. In within group comparison of pupil size, differences between RP and FHO were significant in infrared conditions. Control subjects increased, whereas TMD patients decreased pupil size at FHO in infrared lightening. FHO/RP ratio in darkness and light/darkness ratio in RP were significantly different between groups. Taken together, these data suggest that TMD subjects have an impairment of the sympathetic-adrenergic component of the ANS to be activated under stress. The present study provides preliminary pupillometric data confirming that adrenergic function is dysregulated in patients with TMD.

Effects of bisoprolol and cilazapril on the central retinal artery blood flow in patients with essential hypertension--preliminary results

BACKGROUND

A growing body of evidence suggests that effective blood pressure reduction may inhibit the progression of microvascular damage in patients with essential arterial hypertension. However, the potential influence of anti-hypertensive drugs on ocular circulation has not been studied sufficiently.

PURPOSE

The aim of our study was to evaluate the effects of anti-hypertensive therapy on blood flow in the central retinal artery in patients with systemic arterial hypertension.

MATERIAL AND METHODS

Twenty patients with essential arterial hypertension, aged 32-46 years, were examined with Doppler ultrasonography (10 MHz ultrasound probe). Blood flow velocities, pulsatility, and vascular resistance were determined before and 3 hours after systemic application of either bisoprolol 5 mg or cilazapril 2.5 mg.

RESULTS

Administered bisoprolol significantly decreased maximum (9.8 ± 0.5 cm/s versus 8.5 ± 0.6 cm/s; P < 0.05) and minimum (2.75 ± 0.19 cm/s versus 1.75 ± 0.27 cm/s; P < 0.02) velocity, increased the Pourcellot's index (0.71 to 0.79; P < 0.05) in central retinal artery. There were no statistically significant changes in central retinal artery blood flow after administration of cilazapril.

CONCLUSION

Systemic application of beta-blockers may unfavourably disturb the ocular blood flow.

Beta2-adrenergic receptor signaling mediates corneal epithelial wound repair

PURPOSE

Beta-adrenergic receptor (AR) antagonists are frequently prescribed ophthalmic drugs, yet previous investigations into how catecholamines affect corneal wound healing have yielded conflicting

RESULTS

With the use of an integrated pharmacologic and genetic approach, the authors investigated how the beta-AR impacts corneal epithelial healing.

METHODS

Migratory rates of cultured adult murine corneal epithelial (AMCE) cells and in vivo corneal wound healing were examined in beta2-AR(+/+) and beta2-AR(-/-) mice. Signaling pathways were evaluated by immunoblotting. results. The beta-AR agonist isoproterenol decreased AMCE cell migratory speed to 70% of untreated controls, and this was correlated with a 0.60-fold decrease in levels of activated phospho-ERK (P-ERK). Treatment with the beta-AR antagonist (timolol) increased speed 33% and increased P-ERK 2.4-fold (P < 0.05). The same treatment protocols had no effect on AMCE cells derived from beta2-AR(-/-) mice; all treatment groups showed statistically equivalent migratory speeds and ERK phosphorylation. In beta2-AR(+/+) animals, the beta-AR agonist (isoproterenol) delayed the rate of in vivo corneal wound healing by 79%, whereas beta-AR antagonist (timolol) treatment increased the rate of healing by 16% (P < 0.05) compared with saline-treated controls. In contrast, in the beta2-AR(-/-) mice, all treatment groups demonstrated equivalent rates of wound healing. Additionally, murine corneal epithelial cell expressed the catecholamine-synthesizing enzyme tyrosine hydroxylase and detectable levels of epinephrine (184.5 pg/mg protein).

CONCLUSIONS

The authors provide evidence of an endogenous autocrine catecholamine signaling pathway dependent on an intact beta2-AR for the modulation of corneal epithelial wound repair.

Beta-adrenergic receptor agonists delay while antagonists accelerate epithelial wound healing: evidence of an endogenous adrenergic network within the corneal epithelium

Wound healing is a complex and well-orchestrated biological process. Corneal epithelial cells (CECs) must respond quickly to trauma to rapidly restore barrier function and protect the eye from noxious agents. They express a high level of beta2-adrenergic receptors but their function is unknown. Here, we report the novel finding that they form part of a regulatory network in the corneal epithelium, capable of modulating corneal epithelial wound repair. Beta-adrenergic receptor agonists delay CEC migration via a protein phosphatase 2A-mediated mechanism and decrease both electric field-directed migration and corneal wound healing. Conversely, beta-adrenergic receptor antagonists accelerate CEC migration, enhance electric field-mediated directional migration, and promote corneal wound repair. We demonstrate that CECs express key enzymes required for epinephrine (beta-adrenergic receptor agonist) synthesis in the cytoplasm and can detect epinephrine in cell extracts. We propose that the mechanism for the pro-motogenic effect of the beta-adrenergic antagonist is blockade of the beta2-adrenergic receptor preventing autocrine catecholamine binding. Further investigation of this network will improve our understanding of one of the most frequently prescribed class of drugs.

Change of calcium and cAMP concentration by adrenoceptor agents in cultured porcine corneal endothelial cells

It has been reported that beta-adrenergic receptors are localized in the corneal endothelial cells. In this study, the change of cellular signal transduction, such as intracellular calcium and cAMP, was determined with pure adrenergic agonists and commercial antiglaucoma adrenergic agents. The intracellular calcium of cultured porcine corneal endothelial cells was inhibited by 10 microM isoproterenol and norepinephrine, but enhanced by propranolol and 50 mM KCl. In the case of phenylephrine, calcium mobility did not alter significantly. Verapamil, at 10 microM, decreased intracellular calcium concentration. In the presence of isoproterenol, cellular cAMP concentration increased from 28.8 pmole/mg protein (1 microM) to 42.2 pmole/mg protein (100 microM) compared with control of 6.07 pmole/mg protein. Incubation with commercial adrenergic eye drops, such as betaxolol, caused the cAMP concentration to increase from 21.6 pmole/mg protein (0.0005%) to 39.1 pmole/mg protein (0.05%). Adding commercial levobunolol and timolol into cells caused cellular cAMP to increase from 14.3 pmole/mg protein (0.0005%) to 840.5 pmole/mg protein (0.05%) and from 115.2 pmole/mg protein (0.00025%) to 931.0 pmole/mg protein (0.025%), respectively. However, the preservative, benzalkonium chloride, increased cellular cAMP from 15.4 pmole/mg protein (0.00001 mg/ml) to 1087.4 pmole/mg protein (0.01 mg/ml). It is concluded that the intracellular calcium of corneal endothelium decreases when the cellular adrenergic receptor is activated by agonists. Benzalkonium chloride, due to its preservative in commercial antiglaucoma agents which increases cellular cAMP, may alter corneal endothelial physiology through long-term use.

Beta-adrenergic receptors regulating vascular smooth muscle tone are only localized to the intraocular segment of the long posterior ciliary artery in bovine eye

Beta-adrenergic drugs are important drugs in glaucoma treatment. Their exact mechanism of action is not yet fully understood but a decreased perfusion pressure in the ciliary body due to blockade of vasodilatory beta-adrenoceptors is thought to participate in the reduction of intraocular pressure. This study investigates the vasodilator action of beta adrenergic-agents in intra- and extraocular arteries from bovine and human eyes. Ring segments of retinal, choroidal, intraocular segment of long posterior ciliary artery, and segments of extraocular posterior ciliary arteries from bovine eyes and short posterior ciliary arteries from freshly enucleated human eyes were mounted on an isometric myograph and their reactivity to beta-adrenergic drugs were studied. Of all vessel types examined only the intraocular segment of long posterior ciliary artery precontracted with prostaglandin F2 alpha responded to 1-isoprenaline (1 nM-1 microM) with a graded concentration-dependent relaxation (32 +/- 7%, n = 10) and a pD2 of 7.5 +/- 0.2 concentrations of 1-isoprenaline greater than 1 microM induced contractions which were antagonized by a combined blockade of alpha1- and alpha2-adrenoceptors. Salbutamol (selective beta2-agonist) induced relaxations of similar magnitude as that of 1-isoprenaline but the sensitivity of the intraocular segment of long posterior ciliary arteries to salbutamol was 312 times less than that to 1-isoprenaline, pD2 7.2 +/- 0.2 and 4.4 +/- 0.1 (n = 6), respectively, whereas dobutamine (selective beta 1-agonist) had no effect between 1 nM and 10 microM. Betaxolol (selective beta 1-antagonist) and 1CI 115811 (selective beta 2-antagonist) competitively antagonized isoprenaline-induced relaxations giving pKB-values of 5.9 +/- 0.1 (n = 11) and 8.5 +/- 0.1 (n = 6), respectively. The slope of the Schild-plots were equal to unity. Human posterior ciliary arteries with spontaneous tone or tone induced by 10 microM PGF2 alpha did not react to isoprenaline (1 nM-10 microM). The bovine intraocular segment of long posterior ciliary arteries contracted to 1-noradrenaline without alpha-adrenoceptor blockade and addition of propranolol or cocaine did not change the concentration-response curve. 1-Phenylephrine and B-HT933 induced both potent and strong contractions indicating the presence of both alpha 1- and alpha 2-adrenoceptors in these arteries. Although beta-adrenoceptors have been identified in various parts of the ocular circulation by radio-ligand binding techniques our data show that beta-adrenoceptors linked to regulation of vascular tone are only found in intraocular branches of the intraocular segment of long posterior ciliary artery in bovine eyes.(ABSTRACT TRUNCATED AT 400 WORDS)