Characterization of sensory neurotransmission and its inhibition via α2B-adrenoceptors and via non-α2-receptors in rabbit iris

摘要: To find out whether, and which type of, adrenoceptors mediate prejunctional inhibition of sensory neurotransmitter release from trigeminal fibres, the modulation twitch response to electrical field stimulation on rabbit isolated iris was investigated. Evoked sphincter contractions consisted a minor fast cholinergic large slow component. The latter unaffected by atropine guanethidine, hence nonadrenergic noncholinergic in nature (NANC), but nearly completely abolished capsaicin pretreatment neurokinin receptor antagonist spantide. probably not mediated NK2 receptors as SR 48,968, an selective nonpeptide antagonist, failed reduce endogenous neurokinin(s) (and exogenous substance P), part due NK1 activation shown reduction CP 96,345, non-peptide perhaps NK3 receptors. A small antagonist- capsaicin-insensitive NANC contraction is CGRP α2-adrenoceptor agonist oxymetazoline inhibited evoked (22 nmol/1, IC20; about 40%, maximum inhibition) without affecting (up 1 μmol/1) or postjunctional sensitivity P. antagonized rauwolscine (apparent -log KB 8.04) relatively α2B-adrenoceptor ARC-239 (-log 8.51). α2- imidazoline aganodine (0.25 μmol/l, 30%, P responses. Rauwolscine 0.3 μmol/l antagonize this effect. It concluded that neurotransmitter(s) fibres eye may be α2B-adrenoceptors non-α2-receptor, receptor.