Effects of an LH-releasing hormone antagonist on the secretion of LH, FSH, prolactin and ovarian steroids at different stages of the luteal phase in the stumptailed macaque (Macaca arctoides)

Abstract

The role of the pituitary gonadotrophins in controlling luteal function in the stumptailed macaque has been investigated by examining profiles of serum concentrations of LH, FSH, progesterone and oestradiol in daily blood samples from 13 monkeys during the menstrual cycle, and in blood samples taken at hourly intervals between 09.00 and 21.00 h on different days of the luteal phase in 13 cycles. The effects of acute withdrawal of gonadotrophins was investigated by administering a single injection of 300 micrograms LHRH antagonist/kg body weight at different stages of the luteal phase during 28 cycles. Although there were high basal values and marked fluctuations of bioactive LH during the first 4 days after the LH peak, progesterone profiles showed no corresponding short-term changes, there being a slow and steady rise in progesterone concentrations during the sampling periods. After day 5, basal LH secretion decreased, but high amplitude LH pulses were identified which were associated with episodes of progesterone secretion. Administration of the LHRH antagonist caused a suppression of bioactive LH and progesterone concentrations at all stages of the luteal phase, although some basal secretion of progesterone was maintained through the 24-h period of effective antagonist gonadotroph blockade. Luteal function recovered apparently normally in all monkeys treated in the early-mid-luteal phase. Serum concentrations of FSH and oestradiol fluctuated comparatively less during the 12-h sampling periods, and the antagonist had less suppressive effects on the concentrations of these hormones. The LHRH antagonist had no apparent effect on prolactin release.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of GnRH antagonist treatment on follicular development and angiogenesis in the primate ovary

“…In contrast, while treatment with GnRH antagonist inhibits gonadotrophin secretion this may have little effect on the ability of hypoxia and local paracrine mechanisms to mediate or modulate VEGF action in the ovarian follicle, as these compensatory mechanisms may be allowed to function. It follows that the reason that GnRH antagonist treatment is more effective in suppressing early luteal angiogenesis ) is likely to be because the corpus luteum is heavily dependent upon LH (Fraser et al 1986). This dependence would include the local compensatory mechanisms that are relatively gonadotrophin independent in the developing follicle.…”

Blockade of the oestrogen-induced LH surge in the ovariectomized common marmoset (Callithrix jacchus) by an LHRH antagonist

“…The 6 animals were treated with the LHRH antagonist, at a dose of 300 pg/kg, on two separate occasions. This dose was selected on the basis of previous studies in stump-tailed and crab-eating macaques (Adams et al, 1986;Fraser et al, 1986).…”

“…LH was determined using an in-vitro bioassay based on the production of testosterone by dispersed mouse Leydig cells as described previously (Fraser et al, 1986). Sensitivity of the assay was 2 ng LH/ml using the rhesus monkey pituitary standard RP-1, supplied by the National Institute of Child Health and Human Development, Bethesda, MD, USA.…”

Inhibition of Early Luteal Angiogenesis by Gonadotropin-Releasing Hormone Antagonist Treatment in the Primate

“…It is well established that LH is the major luteotrophic factor regulating the function of the primate CL. Withdrawal of LH by GnRH antagonist administration results in luteolysis of the CL in the Old World primate (2), New World primate (3), and women (4), as reflected by decreased plasma progesterone levels.…”