title: The effect of serotonin on the rabbit isolated iris sphincter muscle.
abstract: The rabbit isolated iris sphincter muscle maintained in an isotonic state is unaffected by applied serotonin (5-hydroxytryptamine or 5-HT) whereas carbachol causes the muscle to contract. Serotonin does, however, produce a relaxation of the contracted muscle in a dose-dependent manner. This effect is also induced by the 5-HT receptor agonists 8-OH-DPAT (8-hydroxy-2-[di-n-propyl-amino] tetralin, RU 24969 (5-methoxy-3-[1,2,3,6, tetrahydro-4-pyridinyl]-1-indole) and ipsapirone, suggesting the involvement of 5-HT1A receptors. This view is supported by the finding that metergoline, methysergide and propranolol all counteracted the effect produced by serotonin. While 5-HT3 receptors are not involved in the described process, a minor involvement of 5-HT2 receptors cannot be excluded as methysergide partially counteracted the serotonin response. These data provide evidence that serotonin receptors, in particular the 5-HT1A subtype, may be associated with the iris sphincter muscle and suggest their involvement in the regulation of pupil size.
authors.affiliation: Nuffield Laboratory of Ophthalmology, University of Oxford, UK.
authors.forename: N L
authors.initials: NL
authors.lastname: Barnett
authors.forename: N N
authors.initials: NN
authors.lastname: Osborne
mesh_terms: D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007498:Iris / Q000187:drug effects* / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects* / Q000502:physiology; D011817:Rabbits; D011985:Receptors, Serotonin / Q000187:drug effects; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology
chemical_list: D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D012701:Serotonin; D002217:Carbachol