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1. Effects of drugs acting on adrenergic and adenosine receptors on the intraocular pressure and the activity of adenylyl cyclase in ciliary processes and their sensitivity to pertussis toxin

Creator:
Čepelík, J., Caicedo, M., Dědina, M., and Hynie, S.
Type:
article, model:article, and TEXT
Subject:
adenosine agonists, adenylyl cyclase, adrenergic agonists, intraocular pressure, and pertussis toxin
Language:
English
Description:
The effects of the selective alpha2-adrenergic agonist p-aminoclonidine, the nonselective adrenergic agonist epinephrine, the selective beta2-adrenergic agonist fenoterol and the adenosine Ai agonist R-PLA on intraocular pressure were studied in control and pertussis toxin-pretreated rabbits. Pretreatment of rabbits with pertussis toxin decreased the ocular hypotensive effects of p-aminoclonidine and epinephrine, did not influence the same effects of fenoterol or R-PIA and markedly potentiated the initial ocular hypertensive effects of epinephrine and R-PIA. As far as the action on adenylyl cyclase in ciliary processes is concerned, isoproterenol stimulated its activity in control rabbits and epinephrine exerted dual, i.e. stimulatory and inhibitory effects on the activity of this enzyme. The data obtained with epinephrine and p-aminoclonidine confirm the view that their ocular hypotensive effects are associated with their inhibitory action on adenylyl cyclase and contradict the opinion that the hypotensive action of adrenergic drugs depends on adenylyl cyclase activation.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

2. The effects of adrenergic agonists on intraocular pressure and on adenylyl cyclase activity of ciliary processes in pigmented rabbits

Creator:
Čepelík, J., Dědina, M., and Hynie, S.
Type:
article, model:article, and TEXT
Subject:
adenylyl cyclase, adrenergic agonists, ciliary processes, desensitization, and intraocular pressure
Language:
English
Description:
The effects of /¿-adrenergic agonists isoprenaline, fenoterol and clenbuterol on the activity of adenylyl cyclase from ciliary processes and on intraocular pressure were examined in pigmented rabbits. Isoprenaline, fenoterol and clenbuterol stimulated adenylyl cyclase activity in vitro, but clenbuterol behaved as a partial agonist. Preincubation of ciliary processes with any of these three drugs led to the heterologous desensitization of adenylyl cyclase to the stimulatory effects of beta-adrenergic agonists or vasoactive intestinal peptide (VIP). This desensitization was dose-dependent and was expressed mainly as a decrease of the highest effects of stimulatory drugs. The exact mechanism of this phenomenon is not yet known. After topical administration, all three tested /¿-adrenergic agonists decreased intraocular pressure with approximately the same intensity. The relationship between ocular hypotensive effects of /¿-adrenergic agonists and their effects on adenylyl cyclase of ciliary processes is discussed. It is concluded that ocular hypotensive effects of adrenergic agonists and other drugs stimulating adenylyl cyclase cannot be explained simply by stimulation or desensitization of adenylyl cyclase of ciliary processes.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public