title: The time-of-day variation in vascular smooth muscle contractility depends on a nitric oxide signalling pathway.
abstract: The dip in blood pressure during the resting-period is paradoxically associated with an increase in total peripheral resistance and occurs at a time when the vascular response to vasoconstrictor compounds is heightened, and to vasodilators reduced. However, the cellular mechanisms responsible for this time-of-day variation are not well defined. We have investigated the role of nitric oxide synthase (NOS) signalling in the control of contraction in mesenteric resistance arteries using wire myography, combined with quantitative PCR analysis of gene transcription and western blot analysis of protein. Small rings of mesenteric arteries, isolated from rats at two opposing time-points corresponding to the animal's active and resting-period, were mounted in a wire myograph. Vessels exhibited a time-of-day variation in their contractile-response to phenylephrine, with a reduced maximal contraction during the active- versus the resting-period (11.8±0.8 versus 18.6±1.2 mN P<0.001). Vessels preconstricted with phenylephrine were also more responsive to vasodilation with acetylcholine during the active-period, with an EC50 of 58.6±11 versus 232±31 nM in resting-period vessels (P<0.0001). These differences were abolished in the presence of l-NAME. Quantitative RT-PCR reveals a functioning peripheral circadian clock in mesenteric arteries and a 3.3-fold increase in endothelial NO synthase mRNA levels in active- versus resting-period vessels (P<0.001), which translated to a 1.7-fold increase in total eNOS protein (P<0.05). The time-of-day variation in the response of mesenteric resistance vessels to phenylephrine and acetylcholine is dependent on NOS signalling.
authors.affiliation: Department of Cardiovascular Sciences, University of Leicester, Glenfield General Hospital, Leicester, UK.
authors.forename: M
authors.initials: M
authors.lastname: Denniff
authors.affiliation: Department of Cardiovascular Sciences, University of Leicester, Glenfield General Hospital, Leicester, UK.
authors.forename: Helen E
authors.initials: HE
authors.lastname: Turrell
authors.affiliation: Department of Cardiovascular Sciences, University of Leicester, Glenfield General Hospital, Leicester, UK.
authors.forename: Andrew
authors.initials: A
authors.lastname: Vanezis
authors.affiliation: Department of Cardiovascular Sciences, University of Leicester, Glenfield General Hospital, Leicester, UK. Electronic address: gcr4@le.ac.uk.
authors.forename: Glenn C
authors.initials: GC
authors.lastname: Rodrigo
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D057906:Circadian Clocks / Q000502:physiology*; D005786:Gene Expression Regulation; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology; D009213:Myography; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000235:genetics* / Q000378:metabolism; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction; D046509:Tissue Culture Techniques; D014655:Vascular Resistance / Q000187:drug effects / Q000502:physiology; D014662:Vasoconstrictor Agents / Q000494:pharmacology; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: D014662:Vasoconstrictor Agents; D014665:Vasodilator Agents; D010656:Phenylephrine; D009569:Nitric Oxide; D052250:Nitric Oxide Synthase Type III; C496316:Nos3 protein, rat; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester
keywords: Alpha1-adrenergic receptor; Circadian clock; Mesenteric arteries; Nitric oxide synthase; Vasoconstriction