title: Changes in the biological:immunological ratio of basal and GnRH-releasable FSH during the follicular, pre-ovulatory and luteal phases of the human menstrual cycle.
abstract: BACKGROUND
  Significant changes in charge isoform distribution of serum FSH occur throughout the human menstrual cycle. In the present study, we analysed the impact of the changing endocrine milieu characteristic of the menstrual cycle on the capability of basal and gonadotrophin-releasing hormone (GnRH)-releasable FSH to trigger intracellular signal transduction via the human FSH receptor.
  
  
  METHODS
  Seven normal women underwent blood sampling every 10 min for 10 h during the early follicular phase (FP), pre-ovulatory phase (PO) and mid- to late luteal phase (LP) of the menstrual cycle. Serum from successive samples collected across 2 h intervals containing FSH released under baseline and exogenous GnRH-stimulated conditions was tested for bioactivity employing a homologous in-vitro assay.
  
  
  RESULTS
  The biological to immunological (B:I) ratio of basal and GnRH-releasable FSH was significantly (P < 0.05 ) higher at LP (range, 0.83 +/- 0.07 to 1.35 +/- 0.30) than during the FP (0.43 +/- 0.02 to 0.65 +/- 0.04) and PO (0.49 +/- 0.05 to 0.62 +/- 0.06). In all phases, the B:I FSH ratio in baseline samples was similar to those exhibited by samples collected after 10 and 90 microg GnRH administration.
  
  
  CONCLUSIONS
  The selective increase in the capability of the admixture of FSH isoforms circulating during the LP to activate the FSH receptor, apparently represents an additional mechanism through which the anterior pituitary may regulate the maturation of those follicles destined to ovulate during the coming cycle.
authors.affiliation: Research Unit in Reproductive Medicine, Hospital de Ginecobstetricia No. 4 Luis Castelazo Ayala, IMSS, México D.F., Mexico.
authors.forename: T
authors.initials: T
authors.lastname: Zariñán
authors.forename: A
authors.initials: A
authors.lastname: Olivares
authors.forename: D
authors.initials: D
authors.lastname: Söderlund
authors.forename: J P
authors.initials: JP
authors.lastname: Méndez
authors.forename: A
authors.initials: A
authors.lastname: Ulloa-Aguirre
mesh_terms: D000328:Adult; D001681:Biological Assay; D002460:Cell Line; D004958:Estradiol / Q000097:blood; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood / Q000378:metabolism*; D005498:Follicular Phase; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D007668:Kidney; D008183:Luteal Phase; D007986:Luteinizing Hormone / Q000097:blood; D010060:Ovulation; D011374:Progesterone / Q000097:blood; D011962:Receptors, FSH / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D011994:Recombinant Proteins; D015398:Signal Transduction; D014162:Transfection
chemical_list: D011962:Receptors, FSH; D011994:Recombinant Proteins; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone