Oocyte growth and follicular hierarchy may be locally controlled by an inhibin-like protein in the lizard Podarcis sicula.

The lizard Podarcis shows an ovarian annual cycle with three to four ovulatory waves between April and July (reproductive period). In August to September, a refractory stage occurs, followed by a nonreproductive period (October to March), during which the oocytes undergo slow growth and prepare themselves for vitellogenesis and ovulation. In the reproductive period, only a certain number of oocytes start growing, giving rise to a follicular hierarchy, which is controlled by still unknown mechanisms. In the present paper, immunoreactive inhibin was detected in previtellogenetic follicles of the reproductive period, and in particular, in the pyriform cells of the follicular epithelium. As the follicle grew and the pyriform cells disappeared, immunostaining shifted to the oocyte cytoplasm. The smaller follicles did not show any immunoreactivity. In the nonreproductive period, no follicles were labeled. We conclude that in the reproductive period, inhibin characterizes the follicles destined to ovulation and might be one of the main factors controlling follicular hierarchy.