Actions of gonadotropin-releasing hormone analogues in pituitary gonadotrophs and their modulation by ovarian steroids

• Published in: The Journal of steroid biochemistry and molecular biology Vol. 101; no. 2; pp. 118 - 126
• Main Authors: Weiss, Juergen M., König, Stephan J., Polack, Stephan, Emons, Günter, Schulz, Klaus-Dieter, Diedrich, Klaus, Ortmann, Olaf
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-10-2006; Elsevier Science
• Subjects: Animals; Biological and medical sciences; Cells, Cultured; Dose-Response Relationship, Drug; Drug Synergism; Estradiol; Female; Fundamental and applied biological sciences. Psychology; GnRH antagonists; Gonadotropin-Releasing Hormone - analogs & derivatives; Gonadotropin-Releasing Hormone - pharmacology; Gonadotropin-Releasing Hormone - physiology; Hormone Antagonists - pharmacology; LH secretion; Luteinizing Hormone - biosynthesis; Luteolytic Agents - pharmacology; Ovary - metabolism; Pituitary Gland - metabolism; Progesterone; Rats; Rats, Sprague-Dawley; Steroids - pharmacology; Steroids - physiology; Triptorelin Pamoate - pharmacology; Vertebrates: endocrinology; GnRH antagonists; Progesterone; Estradiol; LH secretion; Steroid; Endocrine gland; Secretion; Estrogen; 17β-Estradiol; Gonadotropin RH; Ovarian hormone; Progestagen; Hypothalamic hormone; Ovary; Adenohypophyseal hormone; Modulation; Female genital system; Luteinizing hormone; Pituitary gland; Antagonist; Hormone releasing factor; Sex steroid hormone
• ISSN: 0960-0760; 1879-1220
• DOI: 10.1016/j.jsbmb.2006.06.009

Recently, GnRH antagonists (GnRHant) like cetrorelix and ganirelix have been introduced in protocols of controlled ovarian hyperstimulation for assisted reproductive techniques to prevent premature luteinizing hormone (LH) surges. Here we tested, whether the actions of cetrorelix and the GnRH agonist (GnRHag) triptorelin in gonadotrophs are dependent on the steroid milieu. Furthermore, we characterized the actions of cetrorelix and triptorelin on LH secretion and the total LH pool. Female rat pituitary cells were treated either with 0.1
nM triptorelin for 1, 2, 4 and 6 days or for 1, 3, 5 and 6
h or with 1, 10 or 100
nM cetrorelix for 1, 2, 3 and 5
h or for 10
min. Cells were stimulated for 3
h with different concentrations of GnRH (10
pM–1
μM). For analysis of the total LH pool, which is composed of stored and released LH, cells were lysed with 0.1% Triton X-100 at −80
°C overnight. To test, whether the steroid milieu affects the actions of cetrorelix and triptorelin, cells were incubated for 52
h with 1
nM estradiol (E) alone or with combinations of 100
nM progesterone (P) for 4 or 52
h, respectively. Cells were then treated with 0.1
nM triptorelin for 9
h or 1
nM cetrorelix for 3
h and stimulated for 3
h with different concentrations of GnRH (10
pM–1
μM). The suppressive effect of triptorelin on LH secretion was fully accomplished after 3
h of treatment, for cetrorelix only 10
min were sufficient. The concentration of cetrorelix must be at least equimolar to GnRH to block LH secretion. Cetrorelix shifted the EC50s of the GnRH dose–response curve to the right. Triptorelin suppressed total LH significantly (from 137 to 36
ng/ml) after 1
h in a time-dependent manner. In contrast, only high concentrations of cetrorelix increased total LH. In steroid treated cells the suppressive effects of triptorelin were more distinct. One nanomolar cetrorelix suppressed GnRH-stimulated LH secretion of cells not treated with steroids from 10.1 to 3.5
ng/ml. In cells, additionally treated with estradiol alone or estradiol and short-term progesterone, LH levels were higher (from 3.5 to 5.4 or 4.5
ng/ml, respectively). In cells co-treated with estradiol and progesterone for 52
h LH secretion was only suppressed from 10.1 to 9.5
ng/ml. Steroid treatments diminished the suppressive effect of cetrorelix on LH secretion. In conclusion, the depletion of the total LH pool contributes to the desensitizing effect of triptorelin. The actions of cetrorelix and triptorelin are dependent on the steroid milieu.