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

Paul Alfred Francois Fowler, N. P. Groome, K. H. Al-Gubory

Research output: Contribution to journalArticle

3 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)35-42
Number of pages7
JournalReproduction
Volume126
Issue number1
DOIs
Publication statusPublished - 2003

Keywords

  • gonadotropin-releasing-hormone
  • attenuating factor bioactivity
  • human follicular-fluid
  • luteinizing-hormone
  • messenger-RNA
  • rat pituitary
  • estrous-cycle
  • superovulated women
  • bovine inhibin
  • growth-hormone

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