A gonadotropin-releasing hormone (GnRH) antagonist decreases androgen production and spermatogonial multiplication in frog (Rana esculenta) : indirect evidence for the existence of GnRH or GnRH-like material receptors in the hypophysis and testis
Di Matteo, L.; Minucci, S.; Fasano, S.; Pierantoni, R.; Varriale, B.; Chieffi, G.
Endocrinology 122(1): 62-67
The effects of a GnRH antagonist (GnRHA) on GnRH agonist (GnRH*)-induced androgen production and spermatogonial multiplication were studied in the frog, Rana esculenta, in vivo and in vitro. Intact and hypophysectomized (PDX) animals were kept at 22 .+-. 2.degree.C and treated with GnRH (45 ng/g BW) and GnRH* plus 1.times. and 10.times. concentrations of GnRHA on alternative days for 2 weeks. Androgen concentration in GnRH* plus GnRHA-treated animals decreased in the testis by about 50% with the 10.times. dose whereas the increase obtained in GnRH*-treated PDX group was completely abolished with the 1.times. dose. Histological sections were evaluated with respect of the mitotic index (MI) of the primary spermatogonia. Both GnRHA-treated intact and PDX frogs showed a dose-dependent MI decrease which reached 59% and 57% of control, respectively. In vitro incubations were carried out on testis halves at 15 C for 0, 2, 4, 6, and 8 h with the addition of 1 .mu.g GnRH* and 1 .mu.g GnRH* plus 1 or 10 .mu.g GnRHA. The stimulatory effect of GnRHA* and the inhibitor effect of GnRHA were apparent within 2 h. The basal mitogenic activity was affected by antagonist treatment and the inhibitory effect on the MI was evident within 2-4 h in the 10.times.-treated groups or within 6-8 h in the 1.times. treated groups. Since GnRH* and GnRHA bind to the same receptor these data strongly indicate that the effects of putative GnRH-like materials in the frog, Rana esculenta, are mediated throughout stereospecific recognition sites in both pituitary and testis.