Cadmium in Podarcis sicula Disrupts Prefollicular Oocyte Recruitment by Mimicking FSH Action

ABSTRACT

Cadmium is a highly polluting heavy metal known to have undesirable effects on health in both animals and humans, targeting the kidneys, the liver and the vascular system. A wide spectrum of deleterious effects has been reported also on the reproductive organs and the developing embryo. Cadmium in fact is a strong endocrine disruptor that interferes with functioning of endogenous receptors and hormones causing detrimental effects on offspring production and survival.

In spite of the wide number of studies carried out in laboratory mammals, data on cadmium effects on gonadic tissues, fertility and reproduction of wild terrestrial vertebrates are still limited. In particular, information on the consequences of environmental cadmium exposure on reptiles survival and biodiversity is particularly scanty. Reptiles are presently considered highly susceptible to a number of environmental pollutants and this has contributed to the global decline of several wild populations of turtles, crocodilians and lizards. In addition, several reptile species have been identified as good bioindicators of pollution in their environments due to their persistence in a variety of habitats, wide geographic distribution, longevity and site fidelity.

In consideration of the few data currently available we decided to investigate cadmium effects on oogonial proliferation and oocyte recruitment in a species of lizard and to verify whether this metal acts as an endocrine disruptor. For this purpose, we treated adult females with cadmium or, alternatively, with estradiol, progesterone or follicle stimulating hormone.

Results indicate that cadmium stimulates oogonial proliferation and oocyte recruitment by mimicking the effects exerted by gonadotropins. Treatment, in fact, increases preleptotene and zygotene-pachytene oocytes numbers that reach values comparable to those observed after FSH treatment. These values are significantly different, either lower or higher, from those observed after estradiol or progesterone administration. Results also indicate that the supernumerary oocytes produced after cadmium treatment are destined to degenerate and that fecundity is reduced by a significant increase in follicular atresia.

Keywords:

Lizard, oogonial proliferation, follicular atresia, estradiol and progesterone administration, oocytes hierarchy.