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Physiology and pharmacology of alpha and beta receptors in the eye (summary)
SURVEY OF OPHTHALMOLOGY
VOLUME 33 - SUPPLEMENT - APRIL 1989
Physiology and Pharmacology of Alpha and Beta Receptors in the Eye (Summary) MARVIN L. SEARS,M.D.
Department
Key words. glaucoma
of Ophthalmology
l
alpha receptors timolol
and Visual Science,
l
aqueous flow
Yale University, New Haven,
l
beta receptors
l
Connecticut
ciliary epithelium
l
interaction between beta-adrenergic ligands and the beta-adrenergic receptor of the ciliary processes of the eye. New data imply that stimulation of alpha-adrenergic receptors inhibits the beta,-adrenergic receptor-mediated stimulation of cyclic AMP production. These data suggest that the alpha,-adrenergic and beta,-adrenergic receptors of ciliary processes are linked to the same pool of adenylate cyclase catalytic subunits. These studies give information that can help the interpretation of the paradoxical effects exerted on aqueous flow and intraocular pressure by adrenergic drugs.
The effect of drugs can be used to increase our understanding of the endogenous mechanisms for the development of a net aqueous flow in the eye and how these might be disturbed in diseases or how they could be influenced by drug therapy. Well controlled in vitro laboratory experiments or even acute in vivo studies in animals are certainly different from the complex clinical context of chronic drug administration. Nonetheless, in vitro analysis is essential because relatively small effects of drugs upon a tissue with a mixed population of receptors (that may even neutralize each other) press clinical and physiologic techniques beyond the error of the method utilized. Furthermore, the existing tone of the tissue as defined by receptor interaction, or, as modulated through transmitters, in turn influenced by circadian rhythms, may affect the results of pharmacologic investigations. Adrenergic drug-receptor relationship can be quantified in a well-controlled, in vitro, cell-free system. Beta-adrenergic receptors were studied in crude particulate preparations of the ciliary processes of the eyes of several species by a direct ligandbinding assay using I-hydroxybenzylpindolol and by examining the kinetic and regulatory properties of adenylate cyclase linked to the beta-adrenergic receptors. The K, is comparable to that for betaadrenergic receptors of other tissues. K,,, for stimulation of enzyme activity was of the order expected for a beta-adrenergic-receptor-linked adenylate cyclase, and Kis for inhibition of L-epinephrine stimulation were similar to binding constants for antagonists in other systems. The potency order of agonist activation indicates that ciliary processes contain a predominance of beta,-adrenergic receptors. Binding constants determined by the direct ligand-binding technique and by the assay for adenylate cyclase agree, suggesting that the techniques measure the
References 1. Bill A: Blood circulation and fluid dynamics in the eye. Phyiol Res 55:383, 1975 2. Bill A: The role of ciliary blood flow and ultrafiltration in aqueous humor formation. Exp Eye Res 16:287-298, 1973 3. Jumblatt JE, Liu JGH, North CT: Alphas-adrenergic modulation of norepinephrine secretion in the perfused rabbit iris-ciliary body. Cwr Eye Res 6:767-777, 1987 4. Mittag TW, Tormay A: Adrenergic receptor subtypes in rabbit iris-ciliary body membranes: Classification by radioligand studies. Exp Eye Res 40:239-249, 1985 5. Mittag TW, Tormay A, Severin C, et al: Alpha-adrenergic antagonists: Correlation of the effect on intraocular pressure and on alpha*-adrenergic receptor binding specificity in the rabbit eye. Exp Eye Res 40:591-600, 1985 6. Nathanson JA: Adrenergic regulation of intraocular pressure: Identification of betas-adrenergic-stimulated adenylate cyclase in ciliary process epithelium. Proc Nat1 Acad Sci USA 77:7420-7424, 1980 7. Nathanson JA: Human ciliary process adrenergic receptor: Pharmacological characterization. Invest Ophthalmol Vzc Srt 21:798-804, 1981 studies on the mechanism of 8. Neufeld AH: Experimental action of timolol. Sun, Ophthalmol 23:363-370, 1979 9 Neufeld AH, Page ED: In vitro determination of the ability of drugs to bind to adrenergic receptors. Inves;2Ophthalmol Vis Sci lhtll18-1124, 1977 10 Sears ML: Perspectives in the medical treatment of glaucoma, in Krieglstein GK, Leydhecker W (eds): Medihamentosp Glauckomtherapie. Munich, Bergman JF, 1982, pp 49-58 451
452
Surv Ophthalmol 33 (Supplement) April 1989
1 1. Sears ML: Autonomic nervous system: Adrenergic agonists, in Sears ML (ed): Phurmacology ofthe Eye, 69, Ch. 5a, Berlin, Heidelberg, Springer-Verlag, 1984, pp. 193-248 12. Sears ML: Regulation of aqueous flow by the adenylate cyclase receptor complex in the ciliary epithelium. Am J Ophthalmol1OO:194-198, 1985 13. Sears ML, Gregory DS, Bausher LP, et al: The beta adrenergic receptor and adenyl cyclase of rabbit ciliary processes, in Sears ML (ed): New Directions in Ophthulmti Research. New Haven, Yale University Press, 1981, pp 127-148 14. Sears ML, Gregory DS, Bausher LP: Interaction between alphas- and betas-adrenergic receptors in rabbit cihary processes. Curr Eye Res 6:497-505, 1987 15. Sears ML, Gregory DS, Bromberg BB: Beta adrenergic receptors in ciliary processes ofthe rabbit. Invest Ophthalmol Vis Sci 19:203-207, 1980 16. Sears ML, Neufeld AH, Jampol LM, et al: Cyclic AMP in the aqueous humor: the effects ofadrenergic agents. Exp Eye Res 14:242-250, 1972 17. Sears ML, Vareilles P, Silverstone D, et al: Comparison of
the effects of timolol and other adrenergic agents on intraocular pressure in the rabbit. Invest Ophthalmol Vis S,ci 16:96&987, 1977 18. U’prichard DC, Mitrius JD, Kahn DJ, et al: The alphaaadrenergic receptor: multiple affmity states and regulation of a receptor inversely coupled to adenylate cyclase, in Segawa T, Yamamura HI, and Kyriyama K (eds): Molecular Pharmacology of Neurotransmitter Receptors, Vol 36, 19. Waitzman MB, Woods WD: Some characteristics of an adenyl cyclase preparation from rabbit cihary process tissue. Exp Eye Res 12:99-111, 1971 20. Woodcock KA, Johnston CI: Alpha-adrenergic receptors modulate beta-receptor affinity in rat kidney membranes. Nature 286:59, 1980
Author’s address: Department of Ophthalmology and Visual Science, Yale University School of Medicine, P.O. Box 3333, New Haven, CT 06510.
VOLUME 33 - SUPPLEMENT - APRIL 1989
Physiology and Pharmacology of Alpha and Beta Receptors in the Eye (Summary) MARVIN L. SEARS,M.D.
Department
Key words. glaucoma
of Ophthalmology
l
alpha receptors timolol
and Visual Science,
l
aqueous flow
Yale University, New Haven,
l
beta receptors
l
Connecticut
ciliary epithelium
l
interaction between beta-adrenergic ligands and the beta-adrenergic receptor of the ciliary processes of the eye. New data imply that stimulation of alpha-adrenergic receptors inhibits the beta,-adrenergic receptor-mediated stimulation of cyclic AMP production. These data suggest that the alpha,-adrenergic and beta,-adrenergic receptors of ciliary processes are linked to the same pool of adenylate cyclase catalytic subunits. These studies give information that can help the interpretation of the paradoxical effects exerted on aqueous flow and intraocular pressure by adrenergic drugs.
The effect of drugs can be used to increase our understanding of the endogenous mechanisms for the development of a net aqueous flow in the eye and how these might be disturbed in diseases or how they could be influenced by drug therapy. Well controlled in vitro laboratory experiments or even acute in vivo studies in animals are certainly different from the complex clinical context of chronic drug administration. Nonetheless, in vitro analysis is essential because relatively small effects of drugs upon a tissue with a mixed population of receptors (that may even neutralize each other) press clinical and physiologic techniques beyond the error of the method utilized. Furthermore, the existing tone of the tissue as defined by receptor interaction, or, as modulated through transmitters, in turn influenced by circadian rhythms, may affect the results of pharmacologic investigations. Adrenergic drug-receptor relationship can be quantified in a well-controlled, in vitro, cell-free system. Beta-adrenergic receptors were studied in crude particulate preparations of the ciliary processes of the eyes of several species by a direct ligandbinding assay using I-hydroxybenzylpindolol and by examining the kinetic and regulatory properties of adenylate cyclase linked to the beta-adrenergic receptors. The K, is comparable to that for betaadrenergic receptors of other tissues. K,,, for stimulation of enzyme activity was of the order expected for a beta-adrenergic-receptor-linked adenylate cyclase, and Kis for inhibition of L-epinephrine stimulation were similar to binding constants for antagonists in other systems. The potency order of agonist activation indicates that ciliary processes contain a predominance of beta,-adrenergic receptors. Binding constants determined by the direct ligand-binding technique and by the assay for adenylate cyclase agree, suggesting that the techniques measure the
References 1. Bill A: Blood circulation and fluid dynamics in the eye. Phyiol Res 55:383, 1975 2. Bill A: The role of ciliary blood flow and ultrafiltration in aqueous humor formation. Exp Eye Res 16:287-298, 1973 3. Jumblatt JE, Liu JGH, North CT: Alphas-adrenergic modulation of norepinephrine secretion in the perfused rabbit iris-ciliary body. Cwr Eye Res 6:767-777, 1987 4. Mittag TW, Tormay A: Adrenergic receptor subtypes in rabbit iris-ciliary body membranes: Classification by radioligand studies. Exp Eye Res 40:239-249, 1985 5. Mittag TW, Tormay A, Severin C, et al: Alpha-adrenergic antagonists: Correlation of the effect on intraocular pressure and on alpha*-adrenergic receptor binding specificity in the rabbit eye. Exp Eye Res 40:591-600, 1985 6. Nathanson JA: Adrenergic regulation of intraocular pressure: Identification of betas-adrenergic-stimulated adenylate cyclase in ciliary process epithelium. Proc Nat1 Acad Sci USA 77:7420-7424, 1980 7. Nathanson JA: Human ciliary process adrenergic receptor: Pharmacological characterization. Invest Ophthalmol Vzc Srt 21:798-804, 1981 studies on the mechanism of 8. Neufeld AH: Experimental action of timolol. Sun, Ophthalmol 23:363-370, 1979 9 Neufeld AH, Page ED: In vitro determination of the ability of drugs to bind to adrenergic receptors. Inves;2Ophthalmol Vis Sci lhtll18-1124, 1977 10 Sears ML: Perspectives in the medical treatment of glaucoma, in Krieglstein GK, Leydhecker W (eds): Medihamentosp Glauckomtherapie. Munich, Bergman JF, 1982, pp 49-58 451
452
Surv Ophthalmol 33 (Supplement) April 1989
1 1. Sears ML: Autonomic nervous system: Adrenergic agonists, in Sears ML (ed): Phurmacology ofthe Eye, 69, Ch. 5a, Berlin, Heidelberg, Springer-Verlag, 1984, pp. 193-248 12. Sears ML: Regulation of aqueous flow by the adenylate cyclase receptor complex in the ciliary epithelium. Am J Ophthalmol1OO:194-198, 1985 13. Sears ML, Gregory DS, Bausher LP, et al: The beta adrenergic receptor and adenyl cyclase of rabbit ciliary processes, in Sears ML (ed): New Directions in Ophthulmti Research. New Haven, Yale University Press, 1981, pp 127-148 14. Sears ML, Gregory DS, Bausher LP: Interaction between alphas- and betas-adrenergic receptors in rabbit cihary processes. Curr Eye Res 6:497-505, 1987 15. Sears ML, Gregory DS, Bromberg BB: Beta adrenergic receptors in ciliary processes ofthe rabbit. Invest Ophthalmol Vis Sci 19:203-207, 1980 16. Sears ML, Neufeld AH, Jampol LM, et al: Cyclic AMP in the aqueous humor: the effects ofadrenergic agents. Exp Eye Res 14:242-250, 1972 17. Sears ML, Vareilles P, Silverstone D, et al: Comparison of
the effects of timolol and other adrenergic agents on intraocular pressure in the rabbit. Invest Ophthalmol Vis S,ci 16:96&987, 1977 18. U’prichard DC, Mitrius JD, Kahn DJ, et al: The alphaaadrenergic receptor: multiple affmity states and regulation of a receptor inversely coupled to adenylate cyclase, in Segawa T, Yamamura HI, and Kyriyama K (eds): Molecular Pharmacology of Neurotransmitter Receptors, Vol 36, 19. Waitzman MB, Woods WD: Some characteristics of an adenyl cyclase preparation from rabbit cihary process tissue. Exp Eye Res 12:99-111, 1971 20. Woodcock KA, Johnston CI: Alpha-adrenergic receptors modulate beta-receptor affinity in rat kidney membranes. Nature 286:59, 1980
Author’s address: Department of Ophthalmology and Visual Science, Yale University School of Medicine, P.O. Box 3333, New Haven, CT 06510.