GnRH-induced gonadotrophin secretion in ovariectomized Booroola ewes with hypothalamic--pituitary disconnection

Abstract

To test whether the F gene-specific differences in the plasma concentrations of FSH and LH are due to differences in the pituitary responsiveness to exogenous GnRH, ovariectomized Booroola ewes with hypothalamic-pituitary disconnection (HPD-ovx) were treated with GnRH (250 ng i.v.) once every 2 h for up to 5 weeks. In Exp. 1, jugular venous blood was collected once weekly from 13 FF and 14 ++ HPD-ovx ewes for 6 weeks before GnRH treatment and every 2nd, 3rd or 6th day for 5 weeks during treatment. In Exp. 2, jugular venous blood was collected from another 8 FF and 7 ++ HPD-ovx ewes at 5- or 10-min intervals over 4 GnRH pulses (250 ng i.v. once every 2 h) on 3 separate occasions after the animals had been subjected to the GnRH pulse regimen for approximately 7 days beforehand. Also in Exp. 2, the animals were extensively sampled around a larger (10 micrograms) i.v. injection of GnRH and the pituitary FSH and LH contents assessed after the animals had been re-exposed to the once every 2 h GnRH (250 ng i.v.) pulse regimen for several days following the larger GnRH bolus. In Exp. 3 the distributions of mean plasma concentrations of FSH and LH in individual GnRH-treated HPD-ovx ewes were compared with those in ovariectomized and ovary-intact FF and ++ ewes. During the 6 weeks before GnRH treatment (Exp. 1), the plasma concentrations of FSH (approximately 1 ng/ml) and LH (less than or equal to 0.8 ng/ml) were not different between the genotypes. After GnRH treatment both the mean FSH and LH concentrations increased significantly (P less than 0.01) above basal values after 2 days with F gene-specific differences being noted for FSH but not LH (FSH; FF greater than ++; P less than 0.05). Thereafter, the mean FSH but not LH concentrations increased at a faster rate in FF than in ++ ewes with the overall mean FSH concentrations between the genotypes being significantly different (P less than 0.05). In Exp. 2 considerable between-animal variation in the pulsatile pattern of FSH but not LH concentrations was seen in ewes of both genotypes during GnRH treatment. The overall mean FSH concentrations were higher in FF than in ++ ewes (P less than 0.05) and the mean FSH response to each GnRH pulse was significantly higher in FF than in ++ ewes (P less than 0.05).(ABSTRACT TRUNCATED AT 400 WORDS)

Gonadotrophin-releasing hormone and the control of ovulation rate by the FecB gene in Booroola ewes

“…pulse regimen, the mean plasma i-FSH concentrations increased from about 0.4ngml_I to between 1.0 and 1.4ngml~\ At the end of the pretreatment period, the concentrations of i-FSH were similar to those found for intact Booroola ewes with the BB ewes having significantly higher overall means than the ++ animals. In HPD animals that had been ovariectomized, exogenous GnRH treatment also led to a gene-specific difference in i-FSH (McNatty et al, 1991b). These findings suggest that in the present study the differences between the Booroola genotypes in plasma i-FSH were at least in part due to a difference in the pituitary response to exogenous GnRH rather than to ovarian hormone feedback.…”

The activin receptor-like kinase 6 Booroola mutation enhances suppressive effects of bone morphogenetic protein 2 (BMP2), BMP4, BMP6 and growth and differentiation factor-9 on FSH release from ovine primary pituitary cell cultures

“…This interpretation is based on the reports which show that Booroola sheep have not always showed consistent differences in plasma FSH concentrations or in pituitary FSH secretion (Driancourt et al 1991, McNatty et al 1991a,b, Souza et al 1997, Montgomery et al 2001, Campbell et al 2003. Additionally, the possibility of a second mutation being present in the New Zealand Booroola flock has been raised (Farquhar et al 2006).…”

“…The first study determined concentrations of FSH and luteinising hormone (LH) in ovary-intact ewes (McNatty et al 1987), followed by a subsequent comparison in ovariectomised homozygous Booroola (BB) and non-carrier ewes (McNatty et al 1989). In these flocks, the evidence was that the fecundity gene (FecB) influenced the plasma concentrations of FSH (McNatty et al 1991a, Montgomery et al 1992. The plasma concentrations of FSH were found to be consistently higher in the homozygous Booroola ewes compared with the wild-type (WT) ewes throughout the oestrous cycle, anoestrus and after ovariectomy.…”

“…The plasma concentrations of FSH were found to be consistently higher in the homozygous Booroola ewes compared with the wild-type (WT) ewes throughout the oestrous cycle, anoestrus and after ovariectomy. They were also found to be higher in ovariectomised or ovary-intact ewes treated with gonadotrophin-releasing hormone (GnRH) following hypothalamic-pituitary disconnection (HPD; McNatty et al 1987McNatty et al , 1989McNatty et al , 1991aMcNatty et al , 1993. When HPD or Deslorelin-treated (GnRH agonist) homozygous ALK6 (BB) and WTewes were administered identical doses of FSH, the ovulation rate and plasma concentrations of FSH in those animals which ovulated was the same in both genotypes (Hudson et al 1999).…”

Genes controlling ovulation rate in sheep

“…In most of these reports, gene-specific differences were not found for LH. Overall, the evidence indicates that the BB animals have a greater FSH output per cell relative to ++ animals (McNatty et al, 1991;Heath et al, 1996). For example, in studies with ovariectomized hypothalamic-pituitary disconnected (HPD) animals, the FSH concentration 10 min after an exogenous pulse of GnRH (250 ng) was 1.6-fold higher in the BB than in the ++ genotype (McNatty et al, 1991).…”