title: Increased plasma norepinephrine response to yohimbine in elderly men.
abstract: BACKGROUND
  The effects of aging on sympathetic nervous system and adrenomedullary outflow were estimated by the measurement of plasma norepinephrine (NE) and epinephrine (EPI) responses to yohimbine and clonidine in healthy young and healthy older subjects.
  
  
  METHODS
  Yohimbine (0.65 mg/kg), clonidine (5 microg/kg), and placebo were administered on separate days in random order to 5 healthy older men (age 74 +/- 1 years) and 18 healthy young men (age 26 +/- 1 years). NE and EPI were measured by radioenzymatic assay in plasma samples obtained before and 30, 60, and 90 minutes after drug administration.
  
  
  RESULTS
  Plasma NE increases after yohimbine were greater in older men than in young men. but plasma NE decreases following clonidine did not differ between groups. Plasma NE and systolic blood pressure were higher in older men than in young men at baseline but no longer differed 90 minutes after clonidine. Plasma EPI increases after yohimbine and decreases after clonidine did not differ between groups.
  
  
  CONCLUSIONS
  These results suggest increased sympathetic nervous system outflow in human aging that is not a function of reduced responsiveness of alpha-2 adrenoreceptor-mediated feedback inhibition.
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of Washington School of Medicine, Seattle, USA. petrie.eric@seattle.va.gov
authors.forename: E C
authors.initials: EC
authors.lastname: Petrie
authors.forename: E R
authors.initials: ER
authors.lastname: Peskind
authors.forename: D J
authors.initials: DJ
authors.lastname: Dobie
authors.forename: R C
authors.initials: RC
authors.lastname: Veith
authors.forename: M A
authors.initials: MA
authors.lastname: Raskind
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage; D000317:Adrenergic alpha-Antagonists / Q000008:administration & dosage*; D000328:Adult; D000368:Aged; D000375:Aging / Q000187:drug effects* / Q000378:metabolism; D001794:Blood Pressure; D003000:Clonidine / Q000008:administration & dosage; D004837:Epinephrine / Q000097:blood; D006339:Heart Rate; D006801:Humans; D008297:Male; D009638:Norepinephrine / Q000097:blood*; D015016:Yohimbine / Q000008:administration & dosage*
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D015016:Yohimbine; D003000:Clonidine; D009638:Norepinephrine; D004837:Epinephrine