Endocrine Effects of GnRH Agonist Application to Early Pregnant Gilts

Abstract

Abstract. The hypothesis of the present study was that a GnRH agonist application at early pregnancy would alter the pattern of the key reproductive hormones LH and FSH, and subsequently that of estradiol (E2) and especially progesterone (P4), and improve the conditions for embryo survival in early pregnant gilts. Therefore, the endocrine effects of a GnRH agonist (GnRHa) application to gilts (n=11 GnRHa treated, n=9 saline Controls) were studied in blood samples from the Vena cava caudalis. GnRHa injected on Day 12 after insemination induced elevated (P<0.01) LH and FSH levels for at least 180 min. However, subsequent LH concentrations were not altered up to Day 21 of pregnancy. LH pulse number, estimated in 6-h period samples on Days 13, 15 and 17, was not influenced by treatment and pregnancy. LH pulse amplitude was decreased (P<0.05) on Days 13 to 17 in pregnant gilts of both groups, but not in nonpregnant animals. In pregnant GnRHa-treated gilts, the basal LH level was elevated compared with the Controls (P<0.01). Additionally, differences (P<0.05) in basal LH were present between the pregnant and nonpregnant animals. The P4 and E2 secretion pattern was not affected by GnRHa. P4 concentrations increased (P<0.01) from Day 10 to Day 14 regardless of the treatment. P4 revealed a pulse-like pattern, but without a definite relation to the LH pulse characteristics. Also, pregnancy rate (73 vs. 67%) and the number of fetuses (12.8 ± 2.3 vs. 11.6 ± 2.3) were unaffected in the treated and Control gilts, respectively. The present study did not confirm the initial hypothesis that a GnRHamediated LH effect could alter ovarian steroid secretion and favorably support early embryo development and pregnancy outcome. Key words: GnRH-agonist, LH, Pig, Pregnancy, Progesterone (J. Reprod. Dev. 57: [242][243][244][245][246][247][248] 2011) rogesterone from the developing corpus luteum (CL) is the most important driver of endometrial secretion and receptivity for early conceptus development and implantation in pigs [1,2]. About 30% of porcine conceptuses are lost during the peri-implantation period [3], and this period is susceptible to a lack of P4. It has been shown that a concentration of 4 ng/ml P4 in peripheral blood appears to be minimum required for maintenance of pregnancy [4]. Attempts have been undertaken to improve pregnancy rate or reduce pregnancy losses in pigs by steroid or gonadotropin application [5][6][7]. Since steroid treatment may improve litter size [8,9], the question is whether luteal P4 secretion can be enhanced by GnRH-induced LH stimulation. This is because LH is considered to be essential in pigs for support of luteal P4 production and pregnancy outcome as demonstrated by passive immunization with anti-LH serum or blockage of LH secretion and regulation of ovarian function by a GnRH antagonist [10,11].The hypothesis of the present study was that a single GnRH agonist application, given on Day 12 after insemination, would alter the pattern of the key reproductive hormones LH and FSH, and subsequentl...

GnRH‐agonist deslorelin implant alters the progesterone release pattern during early pregnancy in gilts

“…The short‐term enhanced P concentration as seen by Peltoniemi et al () is expected to be a direct response to the GnRH‐agoniststimulated release of LH. The short‐acting GnRH analogue used by Brussow et al () on Day 12 of pregnancy failed to increase vena cava P concentrations on the day after the treatment (Day 13) and did not change P concentrations on Day 15 nor on Day 17 (similar to our results on Day 16). Also, in the study of Virolainen et al () a GnRH ‐antagonist treatment that started at Day 14 of pregnancy, did not affect P patterns from Day 15 to Day 29, even though the treatment appeared to abolish episodic LH release for 3 days.…”

“…Brussow et al () explained their lack of effect on P release by the relative autonomy of the early CL function in the pig, whereas Virolainen et al () considered the variation in individual responses to explain the variation in LH secretory pattern. Our results support the suggestion by Virolainen et al () that basal LH stimulation seems to be sufficient to support CLs’ P production.…”

“…Also, in the study of Virolainen et al (2003) a GnRH-antagonist treatment that started at Day 14 of pregnancy, did not affect P patterns from Day 15 to Day 29, even though the treatment appeared to abolish episodic LH release for 3 days. Brussow et al (2011) explained their lack of effect on P release by the relative autonomy of the early CL function in the pig, whereas Virolainen et al (2003) considered the variation in individual responses to explain the variation in LH secretory pattern. Our results support the suggestion by Virolainen et al (2003) that basal LH stimulation seems to be sufficient to support CLs' P production.…”

“…In a later study, a clear difference between the “local” P (close to the ovary, measured in the vena cava caudalis ) and the “metabolized” P (as measured in the vena jugularis ) was demonstrated, and a direct relationship between LH and P was suggested (Hoving et al, ; Virolainen, Love, Tast, & Peltoniemi, ). Thereafter, Brussow, Schneider, Wollenhaupt, and Tuchscherer () found effects of a short‐acting GnRH‐agonist treatment on LH concentration immediately after the treatment at Day 12 but not on “local” P at Day 13, 15 and 17 of pregnancy (Brussow et al, ). However, the exact nature of the relationship between LH and P remains unclear and the chronic effect of a long‐acting GnRH‐agonist implant on LH and local P during maternal recognition, rescue of CL and implantation in the gilt is yet not understood.…”

Testicular transcriptional signatures associated with high fertility

“…Serum progesterone was measured by 3 H-radioimmunoassay ( 3 H-RIA) with [1,2,6,7-3H] progesterone tracer (Hartmann Analytic, Germany), as previously described (Brussow et al 2011). Briefly, 50 µL of serum in duplicates (n = 14 per group) was analysed with an incubation step at 37°C for 30 min and at 4°C for 2 h. The B/F (bound to free antigen) separation was performed by the dextran-charcoal method.…”