Effect of chronic treatment with a GnRH agonist (Goserelin) on LH secretion and early pregnancy in gilts

A slow release implant containing the gonadotrophin-releasing hormone (GnRH) analogue Goserelin acetate (D-Ser[But]6, Azgly-NH210)a for GnRH receptor down-regulation in the pituitary was used in gilts, to determine what effects elimination of episodic luteinising hormone (LH) peaks may have on progesterone secretion in the oestrus cycle and in early pregnancy, and on the establishment and maintenance of pregnancies. Groups of non-mated and mated gilts were implanted with the GnRH agonist on day of oestrus (Day 0) and on Days 0, 14, 21 and 29 of pregnancy. The GnRH implant caused increased plasma LH concentrations for 38 h with a peak occurring 14 h post treatment, after which there was a prolonged period during which episodic LH release was abolished. A transient increase in progesterone concentration followed GnRH implant insertion and a steep decline on the day of abortion or the 2 days preceding it was seen in the majority of GnRH agonist treated gilts. In the cyclic gilts, the implant did not alter the pattern of progesterone secretion. In all gilts implanted before Day 29, pregnancy failed. However, in 50% of the gilts implanted on Day 29, pregnancy was maintained. In conclusion, these results indicate that episodic LH peaks play an important role in the establishment of pregnancy and are essential for the maintenance of pregnancy before Day 29.