In this study, the measurement both of peripheral gonadotropins (FSH and LH) and of sex steroids in male and female wild anuran, Rana esculenta, was performed during the annual reproductive cycle; moreover, the role of gonadotropins in the vitellogenic process and in ovarian steroidogenesis was investigated through in vitro experiments. LH plasma changes in males showed high values during autumn-winter months and during the mating period, when high androgen levels were found. Conversely, for the first time in male vertebrates, a clear correspondence between plasma FSH and estradiol-17beta (E2) was shown. In females, FSH peak values were found at the beginning of the mating period in parallel with those of plasma vitellogenin (VTG) and E2; in contrast, high LH levels went together with ovarian weight (gonadosomatic index), which is considered a good marker for the plasma sequestration of VTG by growing oocytes. The in vivo results are corroborated by in vitro studies showing the direct effects of both FSH and LH in inducing hepatic VTG synthesis and release in the culture media. Lastly, although it is not yet known whether or not FSH and LH have separate functions in amphibians, it was clearly shown that they induce ovarian steroid production. These results are discussed in terms of the high seasonality previously demonstrated in this wild frog.

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A 1200-bp cDNA encoding Xenopus laevis deoxyribonuclease I (X. laevis DNase I) was constructed from the total RNA of a X. laevis pancreas using a rapid amplification of cDNA ends method. When the cDNA was transiently transfected into COS-7 cells, the recombinant polypeptide exhibited similar enzymological properties to those of the native pancreatic DNase I. The recombinant enzyme was considerably more labile than most other vertebrate DNase I enzymes. The X. laevis DNase I polypeptide was larger than any other known vertebrate DNase I, containing a unique Cys-rich stretch of 68 or 70 amino acid residues at the carboxyl terminus, and it had less well conserved binding sites for the Ca2+, G-actin and DNA, and two DNase I signature motifs. These alterations might account for its heat instability.