The pituitary gonadotropin from a Pacific salmon (Oncorhynchus tshawytscha) stimulates adenyl cyclase activity in homogenates of ovaries from goldfish (Carassius auratus) but it is about 36 times less active than carp (Cyprinus carpio) gonadotropin. Moreover, a higher maximal stimulation of the cyclase is obtained with the more homologous (carp) gonadotropin. These results suggest the existence of a partial zoological specificity of teleost gonadotropins in their stimulating action on adenyl cyclase.

No abstract

Summary. Cyclic adenosine monophosphate content in the ovary of the eel (Anguilla anguilla L.). Effect of gonadotropic hormones in vitro.Freshwater european eels never reach sexual maturity naturally but injecting carp gonadotropin (c-GTH) induced sexual development. In vitro, the incubation of pieces of silver eel ovary with c-GTH increased c-AMP levels. The size of the increase depended both on incubation time and hormone concentration (from 0.01 to 10 [L g/ml) and the response could be used as a gonadotropin bioassay. Relative to c-GTH, the GTH from another Teleost, the indian catfish had the same potency in increasing c-AMP concentration in the eel ovary as in inducing spermiation in the frog. On the other hand, the two assays gave very different results in the case of the GTH isolated from a Chondrostean, the sturgeon.The ovaries from c-GTH-treated silver eels, which had undergone some development, showed a smaller in vitro response to gonadotropin than did ovaries from untreated eels. Yellow eel ovaries, which presented few macroscopical changes after in vivo treatment with c-GTH, were as sensitive to gonadotropin in vitro as silver eel ovaries.Introduction.

thermodependence studies also disclosed hormone-dependent differences ; at 5 °C, cAMP concentration was maximal after 40 min with oLH, whereas it was still increasing after 3 h with cGTH. Differences in the properties of phosphodiesterases and/or in the clearance rate of hormone-receptor (HR) complexes could explain these results.The set of RAc systems in eel ovary recognizing fish gonadotropin would then be heterogeneous ; some of them would be endowed with original properties concerning receptor specificity and cAMP diffusion as well as associated phosphodiesterase activity and/or HR metabolism.We suggest that at a stage of evolution when a single sensu stricto GTH is present (instead of two in tetrapods), « isoreceptors », differing in specificity and in their fate after hormone binding, could be an important element in the fine regulation of gonadal functions.