CHANGES IN OVARIAN FOLLICLES AND IN-VITRO SEX-HORMONE RELEASE IN THE LIZARD PODARCIS-SICULA-SICULA

An in vitro superfusion method was used to test sex hormone release fr om different kinds of ovarian follicle (growing follicles, postovulato ry follicles, and atretic follicles) in the lizard Podarcis sicula sic ula. Sex hormone output changes with the stage of follicle evolution a nd sexual cycle. Previtellogenetic follicles prevail in early-spring q uiescent ovaries and secrete mainly progesterone, which is probably ut ilized at that phase to delay ovarian resumption. In the active ovary, progesterone output from previtellogenetic follicles decreases, where as vitellogenetic follicles produce a significant amount of 17beta-est radiol, which is necessary for sustaining vitellogenin synthesis by th e liver and oviduct growth. As follicles become ripe, progesterone pro duction is resumed, and it increases in young postovulatory follicles. This is in line with the functions assigned to the hormone at that ph ase of the sexual cycle, i.e., the induction of oocyte maturation and the regulation of egg retention in the oviduct. Postovulatory follicle s can also synthetize 17beta-estradiol. After oviposition, this hormon e, which is secreted by the old postovulatory-follicles, can reinitiat e vitellogenin synthesis, allowing the development of a new oocyte set . Our data confirm that active, although ephemeral, corpora lutea are also formed in oviparous species. A limited contribution to ovarian se x steroid production derives also from atretic follicles, at least at the early stages of the breeding cycle. (C) 1993 Wiley-Liss, Inc.