title: Phase difference between serum prolactin and cortisol rhythms is related to body mass index in humans.
abstract: BACKGROUND
  Prolactin (PRL) has many effects in animals and man. For example, it regulates fat mass in fish, birds, and mammals. In particular, the timing of the serum PRL acrophase in relation to the light-dark cycle or to serum cortisol in constant light conditions determines whether the fat mass increases or decreases, as part of the adaptation to seasons. The role of PRL in this respect has been less well studied in man.
  
  
  OBJECTIVE
  We hypothesized that the timing of the PRL acrophase (time point of peak amplitude of the rhythm) with respect to that of cortisol may be correlated with fat mass [or body mass index (BMI) as proxy] in the human, as observed in animals.
  
  
  METHODS
  Seventy-four subjects were available [mean age, 43 (22-77) yr; mean BMI, 26.8 (18.7-38.4) kg/m(2)].
  
  
  METHODS
  Immunofluorometric PRL assay and cortisol RIA of 10-min blood samples collected for 24 h were followed by cosinor analysis for the estimation of the acrophase.
  
  
  RESULTS
  The time difference between the cortisol and PRL acrophases was positively correlated with BMI (P = 0.002), but not with sex, age, or season.
  
  
  CONCLUSIONS
  In various species, a wide gap between the serum cortisol acrophase and that of PRL leads to fat storage. Our finding is consistent with this observation, although we used BMI as proxy. If an advance shift of the PRL acrophase in relation to that of cortisol is indeed responsible for increased fat mass in man, manipulating the PRL phase may offer an alternative means to treat obesity.
authors.affiliation: Leiden University Medical Center, Department of Endocrinology and Metabolic Diseases, Albinusdreef 2, 2333 ZA Leiden, The Netherlands. f.roelfsema@lumc.nl
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Roelfsema
authors.forename: Hanno
authors.initials: H
authors.lastname: Pijl
mesh_terms: D000328:Adult; D000368:Aged; D001774:Blood Chemical Analysis; D015992:Body Mass Index; D002940:Circadian Rhythm / Q000502:physiology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D006854:Hydrocortisone / Q000097:blood* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D044367:Phase Transition; D011388:Prolactin / Q000097:blood*; D012189:Retrospective Studies; D055815:Young Adult
chemical_list: D011388:Prolactin; D006854:Hydrocortisone