title: Circadian variation of alpha 1-adrenoceptor-mediated pressor response to phenylephrine in man.
abstract: The variability in the pressor effects of the alpha 1-adrenoceptor agonist phenylephrine was observed under placebo conditions in ten healthy subjects in a double blind randomized study. Phenylephrine infusions were administered before administration of placebo (baseline) and 2, 4, 8, 12, 24 and 48 h later. The doses of phenylephrine required to increase systolic blood pressure by 20 mmHg after 8 and 12 h (5.30 and 9.30 pm, 81.4 +/- 15.3 and 71.1 +/- 16.0 micrograms min-1, respectively) were significantly (P < 0.01) less than the baseline values (8.30 am, 108.0 +/- 27.6 g min-1). These results might indicate a circadian variation in the phenylephrine-induced alpha-adrenoceptor-mediated vascular response in healthy subjects. These observations lend further insight into circadian variations of vascular tone that might contribute to circadian rhythms in cardiovascular disease.
authors.affiliation: Department of Therapeutics and Pharmacology, Queen's University of Belfast, Northern Ireland.
authors.forename: T C
authors.initials: TC
authors.lastname: Tham
authors.forename: S
authors.initials: S
authors.lastname: Guy
authors.forename: J G
authors.initials: JG
authors.lastname: Riddell
authors.forename: R G
authors.initials: RG
authors.lastname: Shanks
authors.forename: D W
authors.initials: DW
authors.lastname: Harron
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D000328:Adult; D001794:Blood Pressure / Q000187:drug effects*; D002940:Circadian Rhythm; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D010656:Phenylephrine / Q000008:administration & dosage / Q000494:pharmacology*; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*
chemical_list: D000316:Adrenergic alpha-Agonists; D018340:Receptors, Adrenergic, alpha-1; D010656:Phenylephrine