2 GNRHS FLUCTUATE IN CORRELATION WITH ANDROGEN LEVELS IN THE MALE FROG RANA-ESCULENTA

ChickenII-(cII-) and salmon (s-) GnRH levels have been measured in the male frog Rana esculenta during the annual cycle. The presence of pit uitary binding activity for both peptides and plasma androgen levels h as been investigated in order to give insight into the significance of the dual control exerted by the GnRH forms present in the R. esculent a brain. ChickenII- and s-GnRHs showed high values during the spring-s ummer period. Conversely, while cII-GnRH peaked in February, s-GnRH de clined slowly from February until May. Plasma androgen levels increase d as the peptides decreased during the autumn-winter period. Still hig h androgen levels (but significantly lower as compared with winter con centrations) were found during spring. Using iodinated cII-GnRH, GnRH binding sites were detected in pituitary preparations when the corresp onding peptide concentration decreased in the brain. On the contrary, no binding sites were found using labeled s-GnRH. Our results indicate that cII-GnRH has a hypophysiotropic activity, while the role of s-Gn RH needs to be further investigated. (C) 1993 Wiley-Liss, Inc.