title: Serum response of all-trans and 9-cis isomers of beta-carotene in humans.
abstract: OBJECTIVE
  Little work has been performed on the serum response of various carotene isomers. The present study was carried out to examine the serum response of all-trans and 9-cis isomers of beta-carotene (BC) using frequent blood sample collections at early time points.
  
  
  METHODS
  Serum responses of all-trans BC and a mixture of BC isomers containing 80% 9-cis BC were studied in 15 men by measuring the serum concentrations of BC at 1, 3, 5, 7, 9, 12, and 24 hours after a single large oral dose of all-trans BC or 9-cis BC.
  
  
  RESULTS
  The serum response to an oral dose of all-trans BC (120 mg) significantly increased from baseline at 24 hr (p < 0.004). After an oral dose of a mixture of BC isomers (120 mg, 80% 9-cis BC), the peak concentration of 9-cis BC was significantly greater that baseline values (p < 0.016).
  
  
  CONCLUSIONS
  Increases in serum all-trans BC levels, in part, may be due to greater intestinal absorption, whereas the inability to measure a significant increase in the concentration of 9-cis BC may indicate poor absorption, isomerization to all-trans BC, or a very rapid tissue uptake.
authors.affiliation: Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111, USA.
authors.forename: E J
authors.initials: EJ
authors.lastname: Johnson
authors.forename: N I
authors.initials: NI
authors.lastname: Krinsky
authors.forename: R M
authors.initials: RM
authors.lastname: Russell
mesh_terms: D000328:Adult; D016588:Anticarcinogenic Agents; D006801:Humans; D007408:Intestinal Absorption; D007700:Kinetics; D008297:Male; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D019207:beta Carotene / Q000097:blood* / Q000737:chemistry* / Q000493:pharmacokinetics
chemical_list: D016588:Anticarcinogenic Agents; D019207:beta Carotene