Cholinergic inhibition of adrenergic neurosecretion in the rabbit iris-ciliary body.
The prejunctional effects of cholinergic agents on release of norepinephrine from sympathetic nerve endings were investigated in the isolated, superfused rabbit iris-ciliary body. Stimulation-evoked release of 3H-norepinephrine was inhibited by the cholinergic agonists methacholine, oxotremorine, muscarine, carbamylcholine and acetylcholine (plus eserine), but was unmodified by pilocarpine or nicotine. Agonist-induced inhibition was antagonized selectively by atropine, indicating a muscarinic response. Atropine alone markedly enhanced norepinephrine release, revealing considerable tonic activation of prejunctional cholinergic receptors in this system. Prejunctional inhibition by carbamylcholine was found to completely override the facilitative action of forskolin or 8-bromo-cyclic AMP on neurotransmitter release. Cholinergic and alpha 2-adrenergic effects on neurosecretion were non-additive, suggesting that the underlying receptors coexist at neurotransmitter release sites.
Jumblatt
J E
JE
Department of Ophthalmology, University of Louisville School of Medicine, KY 40202.
North
G T
GT
D000818:Animals; D002924:Ciliary Body / Q000294:innervation*; D000242:Cyclic AMP / Q000502:physiology; D066298:In Vitro Techniques; D007498:Iris / Q000294:innervation*; D009469:Neuromuscular Junction / Q000502:physiology; D009638:Norepinephrine / Q000378:metabolism; D010277:Parasympathomimetics / Q000494:pharmacology*; D011817:Rabbits; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000378:metabolism*; D014316:Tritium
D010277:Parasympathomimetics; D011942:Receptors, Adrenergic, alpha; D014316:Tritium; D000242:Cyclic AMP; D009638:Norepinephrine