title: A monthly cycle in the plasma concentration of GnRH and the glomerular filtered load of GnRH during second trimester pregnancy.
abstract: Six healthy women were examined three times a week during the second trimester. The aim of the study was to test the existence of a monthly cycle in plasma GnRH. Because the kidney plays a dominant part in the elimination of small peptides from the circulation by filtration, the filtered load (P-GnRH x GFR) of GnRH was estimated and tested for a cycle. A mathematical model (parabolas overlaid with a cosine curve and containing parameters for cycle length, cycle amplitude and phase) was used in a multivariate analysis of changes in plasma GnRH, creatinine clearance and GnRH filtered load. We found significant monthly cycles in plasma GnRH (p = 0.003) and in GnRH filtered load (p = 0.004), but no significance for a cycle in creatinine clearance. As an intermediate result we demonstrated that the tubular reabsorption of GnRH was unsaturated for all values of plasma GnRH and GnRH filtered load in question. The increased pregnancy level of plasma GnRH originates in part in the placenta, but we assume that the cycle generator is contained in the maternal neuroendocrine system.
authors.affiliation: Department of Clinical Chemistry, Aalborg Hospital, Denmark.
authors.forename: P O
authors.initials: PO
authors.lastname: Paaby
authors.forename: A
authors.initials: A
authors.lastname: Nielsen
authors.forename: K
authors.initials: K
authors.lastname: Raffin
mesh_terms: D000042:Absorption; D003401:Creatine / Q000378:metabolism; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000097:blood* / Q000378:metabolism / Q000652:urine; D006801:Humans; D007678:Kidney Glomerulus / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism; D009994:Osmolar Concentration; D010507:Periodicity; D011247:Pregnancy / Q000097:blood*; D011262:Pregnancy Trimester, Second
chemical_list: D007987:Gonadotropin-Releasing Hormone; D003401:Creatine