Impairment of early ovarian growth in landlocked Atlantic salmon by an antibody to carbohydrate-rich gonadotropin

Effect of carp gonadotropin (cGTH) and a fraction unabsorbed on concanavalin A-Sepharose obtained from cGTH on vitellogenesis in the hypophysectomized marine teleost Gobius niger

To investigate whether a differential potency on vitellogenesis exists between the carp gonadotropin (cGTH) and fraction I-cGTH (proteins from cGTH unbound on concanavalin A-Sepharose, which represent 5% of cGTH in weight), hypophysectomized Gobius niger were treated with the two hormonal preparations at the same level. Vitellogenesis was checked for synthesis of vitellogenin and yolk incorporation in the ovary by means of immunological studies and histological techniques (light and electron microscopy). In addition, increased synthesis of vitellogenin was induced by injection of estradiol 17 beta together with each gonadotropin to assess the action of the two hormonal preparations on vitellogenin incorporation. Oogenesis was enhanced by cGTH and fraction I-cGTH, and at the same dose levels both treatments produced a similar pattern of stimulation of vitellogenesis. Vitellogenin was found in all the blood samples of animals treated by the hormones (cGTH and fraction I-cGTH) alone. Vesicles of pinocytosis were detected by electron microscopy up to Stage IIIa of oogenesis. When a high synthesis of vitellogenin was induced by exogeneous estradiol 17 beta injections, the two gonadotropic preparations had similar effects in yolk incorporation. cGTH was not less potent than fraction I-cGTH in these processes even though the cGTH preparation contains only 5% of fraction I-cGTH. The contamination of cGTH by a small amount of material unbound on concanavalin cannot be solely responsible for the vitellogenic activity of cGTH which consists of 95% glycoproteins.

Failure of antibody to carbohydrate-rich gonadotropin to inhibit rapid ovarian growth in landlocked Atlantic salmon

The discovery of a carbohydrate-poor gonadotropin has resulted in a reassessment of the role of the classical, carbohydrate-rich gonadotropin (Con A II GtH) in teleost ovarian development. Prolonged treatment of landlocked Atlantic salmon with antibody to Con A II GtH failed to inhibit rapid ovarian growth or accumulation of triglyceride or vitellogenin derivative. Sera from antibody-treated fish showed substantial capacity to bind Con A II GtH indicating that antibody treatment successfully removed endogenous Con A II GtH from the circulation. These results are consistent with previous reports that a factor other than Con A II GtH is responsible for stimulating yolk accumulation.