Antiovulatory Doses of Antagonists of LH‐RH Inhibit LH and Progesterone but not FSH and Estradiol Release

Abstract

The differential regulation of immunoactive FSH and LH secretion by endogenous LH-RH was studied using LH-RH antagonists (Ac-D-Trp1,2, D-Cpa2, D-Lys6, D-Ala10LH-RH (MI-1544) and (Ac-D-Nal1, D-Phe(pCl2), D- Trp3, D-Cit6, D-Ala10LH-RH (SB-030) in ovariectomized (OVX) and regularly cycling rats. Single injections of 10 micrograms and 100 micrograms doses and long-term treatment with 10 micrograms doses of MI-1544 were used in OVX animals. Serum and pituitary LH and FSH, as well as serum estradiol and progesterone was determined by RIA during and/or after the treatment. Single injections of MI-1544 in OVX animals caused prompt (in 2 h) and long-lasting (for more than 24 h) suppression of the serum LH, while no or late decrease (after more than 6 h) of the serum FSH. Long-term treatment with the same analog decreased the serum LH (by 50%) and moderately increased the pituitary LH (by 21%) but did not change the serum and the pituitary FSH concentrations. In normal rats, long-term treatment with both of our analogs also resulted in divergent alterations in the LH and FSH concentrations. Serum LH dropped to undetectable levels,while serum FSH did not change significantly. Pituitary LH increased (by 31 to 41%), while FSH decreased (by 27 to 38%). Marked depression was found in the serum progesterone (by 64%) but no significant change in the serum estradiol levels, after the long-term treatment for 21 days. The ovarian cycles were interrupted, and no ovulation appeared during the treatment. Significant decrease was detectable in the weight of the ovaries (by 46%), whereas the weight of the uteri did not change or slightly elevated (by 22%), after the treatment with SB-030 or MI-1544, respectively.

Protein and mRNA expression of gonadotropin-releasing hormone receptor in yaks during estrus

“…Simultaneously, GnRH and neighboring GnRH neurons stimulate the secretion of LH (Conn et al, 1995;Sealfon et al, 1997). However, the secretion of FSH is less dependent upon GnRH and is instead regulated largely by GnRH-independent factors, including gonadal activins, inhibins, and follistatins (Clarke et al, 1983, Pau et al, 1991, Kovacs et al, 1993. Gonadotropin-releasing hormone-III may act as a weak competitor for the mammalian GnRHR, which does not support the hypothesis that it selectively regulates the release of FSH in cattle (Amstalden et al, 2004).…”

Effects of Paint Thinner Exposure on Serum LH, FSH and Testosterone Levels and Hypothalamic Catecholamine Contents in the Male Rat.

“…29) Administration of antiserum to GnRH abolishes LH release, but has no effect upon FSH secretion. 30) Electrochemical stimulation of hypothalamic ME evokes FSH but not LH release following GnRH antagonist treatment both in vivo and in vitro. 31) In the present study, neither 15 nor 30-d thinner inhalation had any significant effect on serum FSH levels.…”

Evidence that lamprey GnRH-III does not release FSH selectively in cattle

“…However, secretion of FSH is less dependent upon GnRH control and is instead regulated largely by GnRH-independent factors that include gonadal activins, inhibins and follistatins (Clarke et al 1983, Pau et al 1991, Kovacs et al 1993.…”