Adrenoceptor subtypes involved in neurally evoked sympathetic vasoconstriction in the anterior choroid of cats.
Electrical stimulation of the preganglionic cervical sympathetic nerve produced ocular vasoconstrictor responses as measured from the anterior choroid of anesthetized cats using laser-Doppler flowmetry. Ipsilateral nictitating membrane contractions were simultaneously measured as an established index of neural sympathetic activation. The frequency-response relationships for both effectors were nearly linear from 0.125-32 Hz. When elicited at 2-min intervals, submaximal evoked responses of both systems were stable for more than 1 hr. Ocular vasoconstrictor and nictitating membrane responses were blocked in a dose-dependent fashion by intravenous treatment with the non-selective alpha-adrenoceptor antagonist phentolamine (0.1-3.0 mg kg-1) and with phenoxybenzamine (3.0 mg kg-1) as well as with the selective alpha 1-adrenoceptor antagonist, prazosin (10-300 micrograms kg-1). In contrast, neither evoked response was antagonized by alpha 2-adrenoceptor blocker, yohimbine (10-300 micrograms kg-1), nor with rauwolscine (500 micrograms kg-1). No significant alteration in magnitude of ocular vasoconstriction was seen with blockade of either muscarinic (atropine, 1 mg kg-1) or beta-adrenergic (propranolol, 1 mg kg-1) receptors. These results demonstrate the usefulness of laser-Doppler flowmetry in studies of the choroidal circulation and suggest that, as previously established for the nictitating membrane, adrenergic neurogenic vasoconstriction in the anterior segment of the eye is mediated almost exclusively by alpha 1-adrenoceptor mechanisms.
Koss
M C
MC
Department of Pharmacology, University of Oklahoma College of Medicine, Oklahoma City 73190.
Gherezghiher
T
T
D000818:Animals; D002415:Cats; D002829:Choroid / Q000098:blood supply*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D017078:Laser-Doppler Flowmetry; D009541:Nictitating Membrane / Q000502:physiology; D010643:Phenoxybenzamine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology; D013997:Time Factors; D014661:Vasoconstriction / Q000187:drug effects
D018340:Receptors, Adrenergic, alpha-1; D010643:Phenoxybenzamine; D011224:Prazosin; D010646:Phentolamine