Alpha 2-adrenergic and VIP receptors in rabbit ciliary processes interact.
The interaction between alpha 2-adrenergic and VIP receptors has been studied by examining inhibition of VIP-stimulated cyclic AMP production by adrenergic agonists in intact, excised rabbit ciliary processes. Epinephrine, norepinephrine, isoproterenol, dopamine, and the specific alpha 2-adrenergic agonists clonidine and p-aminoclonidine exhibit dose-dependent inhibition of VIP-stimulated cyclic AMP production. I50s, clonidine (0.05 microM) = p-aminoclonidine (0.05 microM) congruent to epinephrine (0.1 microM) less than norepinephrine (2.0 microM) less than isoproterenol (15 microM) = dopamine (15 microM), are consistent with the characteristic binding affinities of these adrenergic agonists for alpha 2-adrenergic receptors. Inhibition of VIP-stimulated cyclic AMP production by clonidine, epinephrine, isoproterenol, and dopamine is blocked by yohimbine but not by prazosin. These data establish the alpha 2-adrenergic specificity of the inhibitory effects observed. We have previously shown that beta 2-adrenergic receptor-mediated stimulation of cyclic AMP production in rabbit ciliary processes is also inhibited by postjunctional alpha 2-adrenergic receptors. These studies support the idea that the catecholamines may regulate aqueous humor formation by inhibiting stimulation of cyclic AMP production via postjunctional alpha 2-adrenergic receptors in ciliary processes.
Bausher
L P
LP
Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, CT 06510.
Gregory
D S
DS
Sears
M L
ML
D000316:Adrenergic alpha-Agonists / Q000378:metabolism; D000818:Animals; D002924:Ciliary Body / Q000378:metabolism*; D000242:Cyclic AMP / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000032:analysis*; D013997:Time Factors; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism*
D000316:Adrenergic alpha-Agonists; D011942:Receptors, Adrenergic, alpha; D014660:Vasoactive Intestinal Peptide; D000242:Cyclic AMP