Postnatal development and histofunctional differentiation of the oviduct in the broad-snouted caiman (Caiman latirostris).

Caiman latirostris is a South American crocodilian species characterized as a sentinel of the presence of endocrine-disrupting compounds (EDCs). Evaluating developmental events in hormone-dependent organs, such as the oviduct, is crucial to understand physiological postnatal development, to identify putative periods of exposure sensitive to EDCs, and/or to identify biomarkers useful to evaluate the effects of EDC exposure. In this study, we describe the histomorphological features of C. latirostris oviducts by establishing the ontogeny of changes at cellular, tissue and molecular levels from the neonatal to the pre-pubertal juvenile stages. Since the histological diagnosis of the adenogenic oviduct lies on a group of features, here we defined a histofunctional score system and a cut-off value to distinguish between preadenogenic and adenogenic oviducts. Our results showed that the maturation of the C. latirostris oviduct is completed postnatally and characterized by changes that mimic the pattern of histological modifications described for the mammalian uterus. Ontogenic changes in the oviductal epithelium parallel changes at subepithelial level, and include collagen remodeling and characteristic spatial-temporal patterns of α-actin and desmin. The expression pattern of estrogen receptor alpha and progesterone receptor evidenced that, even at early postnatal developmental stages, the oviduct of C. latirostris is a target organ of endogenous and environmental hormones. Besides, oviductal adenogenesis seems to be an estrogen-dependent process. Results presented here provide not only insights into the histophysiological aspect of caiman female reproductive ducts but also new tools to better characterize caimans as sentinels of endocrine disruption.

The eggshell features and clutch viability of the broad-snouted caiman (Caiman latirostris) are associated with the egg burden of organochlorine compounds.

Organochlorine compounds (OCCs) are toxic and have been identified as endocrine-disrupting chemicals (EDCs). The broad-snouted Caiman (Caiman latirostris) is an oviparous species widely distributed in South America with potential to accumulate OCCs. The eggshell is formed during passage of the eggs through the oviduct. Since the oviduct is a target of hormone actions, exposure to OCCs could modify eggshell quality, thus affecting clutch viability. Eight clutches were collected from wetlands of Parana River tributaries, in north-eastern Argentina. Two to four eggs per clutch were used to establish the burden of OCCs, eggshell thickness and eggshell porosity. The remaining eggs were incubated in controlled conditions. Ten days after hatching, hatchling survival was assessed. Organochlorine pesticide residues (OCPs) were found in all clutches, while polychlorinated biphenyls (PCBs) were present in all but one clutch. The principal contributors to the OCP burden were members of the DDT family and oxychlordane. Eggshell thickness was 400.9±6.0 µm and, unexpectedly, no association between eggshell thickness and the OCC burden was found. The number of pores in the outer surface was 25.3±4.3 pores/cm². A significant inverse correlation between porosity and OCC burden was found (Pearson r= -0.81, p= 0.01). Furthermore, a decrease in caiman survival with decreased pore density was observed (Pearson r= 0.73, p= 0.04). Our findings highlight another potential negative impact of current and past use of OCCs on wildlife species.

Collagen remodelling in the guinea-pig uterine cervix at term is associated with a decrease in progesterone receptor expression.

In human and guinea-pig parturition, progesterone withdrawal and estrogen action are not mediated by changes in their circulating levels. Instead, these events might be promoted by changes in the responsiveness of the uterus and cervix to progesterone and estrogen via changes in their receptors. In this study, the guinea-pig model was used to investigate whether high levels of progesterone and estrogen at term are associated with regional changes in PR and ERalpha levels in uterus and cervix. PR and ERalpha profiles were established in both subepithelium and the muscular layer of the cervix and the lower uterine horns during pregnancy, parturition and postpartum; while collagen remodelling was measured in the subepithelium. Our data showed that collagen remodelling involved in cervical ripening is temporally and spatially associated with a decrease in PR, whereas high expression of ERalpha is observed. This association was found in the subepithelium of the cervical tissue but not in the same region of the uterus. The muscular region of the cervix and uterus also present a transiently decreased expression of PR while ERalpha levels remain high. Thus, the present results indicate that, before parturition, diminished responsiveness of the cervix to progesterone might be caused by a decrease in PR levels and that this may be the mechanism of functional progesterone withdrawal. The guinea-pig was further validated as an animal model for human parturition studies.