Inverse correlation between baseline inhibin B and FSH after stimulation with GnRH: a study of serum levels of inhibin A and B, pro alpha-C and activin A in women with ovulatory disturbances before and after stimulation withGnRH

Objective: Interest has focused recently on the influences of the polypepti de factors inhibin and activin on the selective regulation of the pituitary secretion of gonadotropins. Design: Measurement of the concentrations of inhibin-related proteins in re lation to the changes in pituitary gonadotropin (FSH, LH) parameters, after GnRH stimulation with a bolus injection of 100 mu g gonadorelin, in 19 wom en with ovulatory disturbances. Methods: Serum levels of inhibin A and B, activin A, and pro alpha-C were m easured using sensitive ELISA kits. Results: Within 60 min after GnRH stimulation, FSH values doubled from 5 to 10 mU/ml (P < 0.001). LH increased 12-fold from 2 to 24 mU/ml (P < 0.001). Activin A showed a significant decrease from 0.47 to 0.36 ng/ml (P < 0.001 ), whereas pro alpha-C increased from 127 to 156 pg/ml (P = 0.039). The med ian inhibin A concentration did not show a significant change between basel ine and the 60 min value, whereas inhibin B was characterized by a minor, b ut not significant, increase in the median from 168 to 179 pg/ml (P = 0.408 ). A significant inverse correlation (P = 0.014) with a mean coefficient of correlation of 0.5516 was found, demonstrating a strong relationship betwe en high inhibin B baseline levels and a small increase of FSH after 60 min. Conclusion: Our results show an interesting correlation between the baselin e inhibin B and the change in FSH before and after GnRH stimulation. A high baseline inhibin B implies only a minor increase of FSH after 60 min.