Induction of precocious puberty in ewe lambs by pulsatile administration of GnRH

Abstract

Circhoral administration (250 ng/h, i.v.) of GnRH induced a preovulatory-like surge of LH and subsequent luteal function in 4 of 4 ewe lambs 1 month before expected date of puberty. Within 12h of the start of pulsatile delivery of GnRH, mean concentrations of immunoactive and bioactive LH increased significantly (P less than 0.05) and the LH surge occurred by 1.8 +/- 0.6 days of treatment. Mean concentrations of serum progesterone were elevated significantly (P less than 0.001) 3 days after the surge. The biopotency of LH (bioactive LH/immunoactive LH) before the GnRH-induced surge of LH did not differ from LH biopotency in ewe lambs receiving circhoral delivery of saline (0.41 +/- 0.05 and 0.46 +/- 0.04, respectively). Biopotency of LH declined markedly at the GnRH-induced LH surge (0.25 +/- 0.04), but biopotency of serum LH was significantly augmented (P less than 0.05) during the period of luteal activity (0.70 +/- 0.07). Regular oestrous cycles were observed in 3 of 4 ewe lambs after the 10-day GnRH treatment period. These results indicate that pulsatile delivery of GnRH is effective in inducing precocious puberty in ewe lambs. Increase in LH biopotency does not appear to be required in the pubertal transition to reproductive cyclicity in this species. Augmented LH biopotency may be important in support of luteal function after first ovulation.

Effect of Maternal Exposure to the Environmental Estrogen, Octylphenol, During Fetal and/or Postnatal Life on Onset of Puberty, Endocrine Status, and Ovarian Follicular Dynamics in Ewe Lambs

“…Therefore, from these results we can suggest that OP may be exerting an anabolic estrogenic effect promoting growth in sheep. It is recognized that neither the gonad nor the anterior pituitary of the immature sheep limit sexual development [49][50][51], and a previous study has demonstrated that delivery of exogenous GnRH during neonatal life was effective in inducing precocious puberty in ewe lambs. The pituitary LH release system in prepubertal ewe lambs is capable of responding when exposed to exogenous estradiol [52,53].…”

“…We therefore hypothesized that the earlier onset of puberty may be associated with a disruption in the characteristics of follicle development. Studies in rats have demonstrated that postnatal exposure to a range of environmental estrogens can disrupt estrous cyclicity [29,31,44,53,56] and block ovulation [49]. Endocrine disrupters could affect follicle wave dynamics by altering steroid receptor function [29] or hypothalamic GnRH release [53].…”

Hormona luteinizante y actividad ovárica en respuesta a kisspeptina-10 y su asociación con IGF-1 y leptina en becerras pre-púberes

“…In 5 mo old heifer calves, GnRH induced a preovulatory surge of LH in 75 % of animals and 25 % of them developed a short-lived CL (16) ; therefore, it is proposed that response of hypothalamus to Kiss-10 and pituitary to GnRH varies with age. That is possible because in prepubertal ewes approaching the onset of puberty, Kiss-10 (18) and GnRH (35) administered every hour by 1 and 10 d respectively, induced an LH surge and luteal function in more than 60 % of the animals. Similarly, 74 % of rats that were approximately 8 d before the onset of puberty, a Kiss-10 treatment given every 12 h for 6 d, advanced the vaginal opening (9) .…”

“…In addition, suppressed levels of circulating leptin by food restriction (9,10) or by application of antibody against leptin in rats (9) , Kiss-10 induced a higher LH rise than control animals who had normal leptin levels; furthermore, Kiss-10 induced puberty in 60 % of underfed rats with low circulanting leptin, whereas none of the control animals with normal y la GnRH (35) administradas cada hora por 1 y 10 días respectivamente, indujeron una oleada de LH y la función lútea en más del 60 % de ellas. De igual manera, en ratas que aproximadamente se encontraban a ocho días del inicio de la pubertad, un tratamiento de Kiss-10 cada 12 h por seis días adelantó la apertura vaginal en 74 % de ellas (9) .…”

Serum Concentrations of Immunoactive and Bioactive Luteinizing Hormone (LH) in Gilts. I. Biopotency of LH Increases during Prepubertal Development1

“…Administration of GnRH in a pulsatile manner has been shown to induce ovulation in a number of species [3][4][5][6][7]. Even before the peripubertal period in gilts, LH release and subsequent follicular development and ovulation are induced by administration of GnRH in a pulsatile manner [8][9][10][11][12].…”