title: Demonstration of a non-steroidal, non-inhibin factor in the ovine corpus luteum of pregnancy that reduces pituitary responsiveness to GnRH-induced LH secretion in vitro.
abstract: The decline in pulsatile LH secretion and pituitary responsiveness to GnRH as pregnancy advances may be due to non-steroidal factors secreted by the ovine corpus luteum of pregnancy. Corpora lutea from ten ewes on days 70-80 of gestation were homogenized, charcoal-treated and, together with charcoal-treated follicular fluid from superovulated women, were subjected to inhibin immunoaffinity chromatography, reducing dimeric inhibin A and B by >90% and abolishing inhibin bioactivity. These preparations were investigated using cultures of rat pituitary cells. GnRH-induced LH and FSH secretion in vitro was reduced by ovine corpus luteum extract and human follicular fluid by 47+/-5% and 42+/-5% of control LH and by 37+/-5% and 50+/-10% of control FSH, respectively (P<0.001). Extracts prepared from corpora lutea and placentae that were collected on days 50, 90 and 120 of pregnancy (five ewes per stage of pregnancy) showed increased GnRH-induced LH-suppressing bioactivity, particularly in the case of the placental extracts, with a threefold increase in activity. When partially purified by pseudochromatofocusing, GnRH-induced LH-suppressing bioactivity in extracts of ovine corpora lutea was identified at pH 5.40 and 5.77. Although these values are similar to published gonadotrophin surge-attenuating factor (GnSAF) bioactivity pI values, a GnSAF-blocking antiserum had no consistent effect on ovine corpus luteum extract GnRH-induced LH-suppressing bioactivity. It was concluded that the ovine corpus luteum of pregnancy contains a non-steroidal, non-inhibin factor, probably not GnSAF, that has the ability to reduce pituitary responsiveness to GnRH in vitro.
authors.affiliation: Department of Obstetrics and Gynaecology, University of Aberdeen, Aberdeen AB25 2ZD, UK. p.a.fowler@abdn.ac.uk
authors.forename: P A
authors.initials: PA
authors.lastname: Fowler
authors.forename: N P
authors.initials: NP
authors.lastname: Groome
authors.forename: K H
authors.initials: KH
authors.lastname: Al-Gubory
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003338:Corpus Luteum / Q000737:chemistry* / Q000378:metabolism; D003864:Depression, Chemical; D005260:Female; D005640:Follicle Stimulating Hormone / Q000032:analysis / Q000378:metabolism; D015571:Follicular Fluid / Q000502:physiology; D042341:Gonadal Hormones; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D006801:Humans; D007106:Immune Sera / Q000494:pharmacology; D007265:Inhibins / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000032:analysis / Q000378:metabolism*; D010902:Pituitary Gland / Q000187:drug effects* / Q000378:metabolism; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011506:Proteins / Q000276:immunology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012756:Sheep / Q000502:physiology*
chemical_list: D042341:Gonadal Hormones; D007106:Immune Sera; D011506:Proteins; C080538:attenuin; D007987:Gonadotropin-Releasing Hormone; D007265:Inhibins; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone