A role for neuropeptide Y in rat iridial arterioles.
A role for neuropeptide Y (NPY) in neurotransmission in rat iridial arterioles has been investigated. Reverse transcription-polymerase chain reaction analysis has demonstrated mRNA expression for both Y1 and Y2 receptors in the superior cervical ganglion and iris. The Y1 agonist [Leu31,Pro34]NPY caused a dose-dependent constriction of iris arterioles (50% effective concentration of 10(-8) M), but, at low concentrations (10(-9) and 10(-10) M), it failed to potentiate either submaximal responses to norepinephrine (10(-6) M) or submaximal, noradrenergic responses to nerve stimulation. In contrast, 10(-7) M [Leu31,Pro34]NPY potentiated submaximal, noradrenergic responses to nerve stimulation (10 Hz, < or = 1 s) and to a concentration of norepinephrine (10(-7) M) which produced only small contractions. The Y1 antagonist 1229U91 blocked contractions induced by [Leu31,Pro34]NPY. Stimulation of the nerves for longer periods (10 or 20 Hz; 5, 30, or 60 s) revealed a component of the response which was reduced by 1229U91. This component was not apparent after brief stimuli (10 Hz, < or = 1 s), even when opposing receptor pathways were blocked. The Y2 agonist N-acetyl-[Leu28,Leu31]NPY24-36 had little effect on arterioles preconstricted with either high potassium or an alpha 2-adrenoceptor agonist, or on nerve-mediated contractions. Results suggest that NPY, released from sympathetic nerves during long-duration, high-frequency stimulation, activates Y1 receptors on iris arterioles to produce vasoconstriction and to potentiate responses to low concentrations of norepinephrine.
Newhouse
M J
MJ
Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, Australia.
Hill
C E
CE
D000818:Animals; D001160:Arterioles / Q000187:drug effects / Q000502:physiology*; D002211:Capsaicin / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D007498:Iris / Q000098:blood supply* / Q000294:innervation; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009478:Neuropeptide Y / Q000031:analogs & derivatives* / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology*; D016133:Polymerase Chain Reaction; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D017476:Receptors, Neuropeptide Y / Q000819:agonists / Q000096:biosynthesis / Q000502:physiology; D014661:Vasoconstriction / Q000187:drug effects
D009478:Neuropeptide Y; D010446:Peptide Fragments; D012333:RNA, Messenger; D017476:Receptors, Neuropeptide Y; C084653:neuropeptide Y (24-36), Ac-(Leu(28,31))-; C097212:neuropeptide Y-Y1 receptor; C095889:neuropeptide Y2 receptor; C062259:neuropeptide Y, Leu(31)-Pro(34)-; D011433:Propranolol; D002211:Capsaicin; D009638:Norepinephrine; D011224:Prazosin