ABSTRACT
Using specific radioimmunoassays for the two GnRH molecular forms present in the European eel, Anguilla anguilla, (mGnRH and cGnRH II), we compared their distributions in the pituitary and different parts of the brain of female silver eels, as well as the modifications of their levels in experimentally matured female eels (treated with carp pituitary extract). In control eels, mGnRH levels were higher than cGnRH II levels in the pituitary, olfactory lobes and telencephalon, di- and mesencephalon, while the opposite was found in the posterior part of the brain (met- and myelencephalon). Experimental sexual maturation of the gonads significantly increased mGnRH levels in the pituitary and anterior parts of the brain; such a positive effect was not observed on the low cGnRH II levels, which were, in contrast, reduced. These data indicate that the positive feedback of gonadal hormones on GnRH, that we previously demonstrated, would specifically affect the mGnRH form. The differential distribution and control of mGnRH and cGnRH II suggest that these two forms have different physiological roles in the eel. The large increase in mGnRH during sexual maturation suggests the prime implication of this form in the neuroendocrine control of reproduction.
ABSTRACT
The effects of sugars and similar additives on the catalytic activity of lysozyme have been attributed (Laretta-Garde et al., Biochim. Biophys. Res. Commun. 155: 816-822 (1988] to a "hydration memory" of the protein for solution conditions to which it was previously exposed. By measuring catalytic activity versus substrate concentration, tryptophan fluorescence and near ultraviolet circular dichroism all in the presence and absence of 50% (w/v) sucrose, we show that the effects can be explained, instead, on the basis of well known properties of proteins.