OVARIAN DEVELOPMENT AND SEX STEROID-HORMONES DURING THE REPRODUCTIVE-CYCLE OF RANA-ESCULENTA COMPLEX

The aim of this work is to investigate the ovarian development of Rana esculenta living in Colfiorito pond (820 m a. s.l.). This process depends on a complex interplay between the estradiol-induced hepatic vitellogenin and the uptake of vitellogenin by the ovary. In order to establish whether the ovarian growth may depend on hydratation process as well, the ovaries have been analyzed-during the annual cycle-by thermo-analysis. As far as we know, this method has been employed for the first time to lower vertebrate tissues with the present work. Vitellogenin titre varies according to a temporal pattern which is characteristic of this mountain population and is well correlated with plasma estradiol concentration. Samples of ovarian tissues, monitored by thermal analysis, show that, in the pre-spawning period three different kinds of water are bonded to the tissues with different energies of interaction. In the ovulatory period, the water is released in one process only. Samples of the post-ovulatory period give the curves, which can be plotted in-between the pre-spawning and ovulatory ones. In conclusion, the present results describe how two different kinds of water are released during the ovarian development. The low weight ovaries, with small oocytes, show a high water percentage which is lost in only one step; the high weight ovaries show a low water percentage, that is lost in three steps. Therefore, in the recovery phase, the ovarian growth, seems mainly due to yolk storage and only partly to the hydratation process which, moreover, is closely related with plasma sex steroid concentration