Agonists nonselective

Alpha agonists, nonselective Epinephrine, dipivefrin Increased outflow, probably via the uveoscleral veins Topical drops... 

Phenylephrine (90) is a selective receptor agonist (+)-niguldipine (91) is a selective antagonist for the receptor. Pra2osin (92) and 5-methylurapidil (93) are nonselective a -receptor antagonists. CEC can differentiate receptors from the other receptors. Pra2osin has low and high affinity for and receptors, respectively. 

Because of the widespread nature of adrenoceptors, nonselective P-agonists can produce many undesirable side effects. Therefore, before adrenergic agonists could become widely used in the treatment of asthma, some selectivity in action was needed. Whereas epinephrine and ephedrine have significant agonist activity at both a and P adrenoceptors, isoproterenol is a selective agonist at the P receptor (39). However, isoproterenol does not distinguish between the P and receptors and it is not active orally. 

Isoproterenol. Isoproterenol hydrochloride is an nonselective P-adrenoceptor agonist that is chemically related to NE. It mimics the effects of stimulation of the sympathetic innervation to the heart which are mediated by NE. It increases heart rate by increasing automaticity of the SA and AV nodes by increasing the rate of phase 4 diastoHc depolarization. It is used in the treatment of acute heart block and supraventricular bradyarrhythmias, although use of atropine is safer for bradyarrhythmias foUowing MI (86). 

Kaumann, A. J., and Marano, M. (1982). On equilibrium dissociation constants for complexes of drag receptor subtypes Selective and nonselective interactions of partial agonists with two P-adrenoceptor subtypes mediating positive chronotropic effects of (-) isoprenaline in kitten atria. Nannyn Schmiedebeberg s Arch. Pharmacol. 219 216—221. 

Adenosine Receptors. Figure 1 Structures of widely used AR agonists, both nonselective and selective. Affinities/potencies at the ARs are found in Table 2. (a) Nucleoside derivatives that are either nonselective or selective for A receptors (1-12). (b) Nucleoside derivatives that are selective for A2a. A2a/A2b (mixed), or A3 receptors (13-19). 

The answer is b. (Hardman, pp 282—283J Central dopamine receptors are divided into Dt and D2 receptors. Antipsychotic activity is better correlated to blockade of D2 receptors. Haloperidol, a potent antipsychotic, selectively antagonizes at Dz receptors. Phenothiazine derivatives, such as chlorpromazine, fluphenazine, and promethazine, are not selective for D2 receptors. Bromocriptine, a selective D2 agonist, is useful in the treatment of parkinsonism and hyperprolactinemia. It produces fewer adverse reactions than do nonselective dopamine receptor agonists... 

Reversible competitive antagonists, nonselective (phentolamine, tolazoline), and -selectively acting (prazosin, terazosin) that reversibly and competitively block a-receptive regions terazosin can last a few hours. At the same time, blockage of a-receptors can be interrupted and stopped by large doses of an agonist such as norepinephrine. 

Sallinen, J., Link, R.E., Haapalinna, A., Viitamaa, T, Kulatunga, M., Sjoholm, B., MacDonald, E., Pelto-Huikko, M., Leino, T., Barsch, G.S., Kobilka, B.K., and Scheinin, M. (1997) Genetic alteration of a2c-adrenoceptor expression in mice influence on locomotor, hypothermic, and neurochemical effects of dexemedetomidine, a subtype-nonselective a2-adrenoceptor agonist. Mol Pharmacol 36 36 6. 

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