Changes in ovarian follistatin levels during the oestrous cycle in sheep may serve as an intraovarian regulator

Activin A and follistatin during the oestrous cycle and early pregnancy in ewes

The activin pathway has been postulated to be involved in regulation of multiple reproductive processes important for survival of the conceptus. These processes include luteinisation of the follicular cells and thus function of the corpus luteum, early embryo development and uterine function including implantation of the conceptus. Therefore, the aim of the current study was to determine whether the concentrations of activin A and follistatin (FST), an activin-binding protein, differed between ewes with a lifetime history of enhanced or reduced embryonic survival (ES). The mRNAs encoding FST and activin A (inhibin beta A subunit; INHBA) were present in the uterus and abundant in the uterine luminal or glandular epithelia by day 18 of gestation. A peak of activin A was observed in the systemic circulation around the time of oestrus, and activin A concentrations were elevated in animals with reduced ES during the oestrous cycle and early gestation. Concentrations of activin A in uterine fluid were approximately twofold greater on day 16 of gestation in ewes with reduced ES compared to those with enhanced ES. No consistent differences in FST were observed between these groups. Treatment of luteinising ovine granulosa cells with activin A in vitro suppressed progesterone secretion providing evidence of a potential pathway whereby increased concentrations of activin A may decrease ES.

Longitudinal analysis of maternal serum Follistatin concentration in normal pregnancy and preeclampsia

OBJECTIVE

Follistatin (FST) is a regulator of the biological activity of activin A (Act A), binding and blocking it, which could contribute to the modulation of its pro-inflammatory activity during pregnancy. We sought to investigate, in this nested case-control study, FST serum levels during normal pregnancy and correlate it with the FST profile in preeclamptic pregnant women, normal pregnant women followed 3 months postpartum and eumenorrheic nonpregnant women throughout the menstrual cycle.

SUBJECTS AND METHODS

Follistatin serum levels determined by ELISA, biochemical and anthropometric variables were measured in normal pregnant (n = 28) and preeclamptic (n = 20) women during three periods of gestation. In addition, FST serum levels were measured in a subset of normal pregnant women (n = 13) followed 3 months postpartum and in eumenorrheic nonpregnant women (n = 20) during the follicular and luteal phases of the menstrual cycle.

RESULTS

Follistatin serum levels in the eumenorrheic nonpregnant and postpartum group were significantly lower when compared to levels throughout gestation (P < 0·01). Serum FST levels increased in each period of pregnancy analysed, being significantly higher towards the end of gestation (P < 0·01). FST levels were lower in late pregnancy in preeclamptic women compared to normal pregnant women (P < 0·05). Finally, FST levels were higher in the luteal phase when compared with the follicular phase of the menstrual cycle (P < 0·05).

CONCLUSIONS

These analyses would permit the consideration that changes in FST levels during pregnancy contribute to the control of the Act A system.

Maternal slaughter at abattoirs: history, causes, cases and the meat industry

Animals of both sexes are slaughtered for meat and meat products at the abattoirs. It has been found in few countries that one-out-of-every-three ewe and one-out-of-every-four doe with single, twin or multiple foetuses are slaughtered in registered slaughterhouses. In quest for meat, numerous viable embryos and foetuses are wasted unnoticed since the productive pregnant animals are not spared in the process. The trend in the slaughter of pregnant animals for meat (ranging from 54.5% to 70.1%) therefore calls for a review to reminisce issues on slaughter reforms, emphasize its implication on losses of genetic materials and sustainability of meat production. As a way of ensuring that welfare quality® assessment is not compromised and cruelty is prevented during animal slaughter, the quantitation of housekeeping genes and naturally occurring microRNAs (miRNAs) are recommended for identifying candidate pain biomarkers. In order to respect consumers’ right however, the manuscript suggests meat branding where the consumption of meat from pregnant animals is ethical.

Intra-ovarian roles of activins and inhibins

Granulosa cells are the main ovarian source of inhibins, activins and activin-binding protein (follistatin) while germ (oogonia, oocytes) and somatic (theca, granulosa, luteal) cells express activin receptors, signaling components and inhibin co-receptor (betaglycan). Activins are implicated in various intra-ovarian roles including germ cell survival and primordial follicle assembly; follicle growth from preantral to mid-antral stages; suppression of thecal androgen production; promotion of granulosa cell proliferation, FSHR and CYP19A1 expression; enhancement of oocyte developmental competence; retardation of follicle luteinization and/or atresia and involvement in luteolysis. Inhibins (primarily inhibin A) are produced in greatest amounts by preovulatory follicles (and corpus luteum in primates) and suppress FSH secretion through endocrine negative feedback. Together with follistatin, inhibins act locally to oppose auto-/paracrine activin (and BMP) signaling thus modulating many of the above processes. The balance between activin-inhibin shifts during follicle development with activin signalling prevailing at earlier stages but declining as inhibin and betaglycan expression rise.

The biology of activin: recent advances in structure, regulation and function

Activin was discovered in the 1980s as a gonadal protein that stimulated FSH release from pituitary gonadotropes and was thought of as a reproductive hormone. In the ensuing decades, many additional activities of activin were described and it was found to be produced in a wide variety of cell types at nearly all stages of development. Its signaling and actions are regulated intracellularly and by extracellular antagonists. Over the past 5 years, a number of important advances have been made that clarify our understanding of the structural basis for signaling and regulation, as well as the biological roles of activin in stem cells, embryonic development and in adults. These include the crystallization of activin in complex with the activin type II receptor ActRIIB, or with the binding proteins follistatin and follistatin-like 3, as well as identification of activin's roles in gonadal sex development, follicle development, luteolysis, beta-cell proliferation and function in the islet, stem cell pluripotency and differentiation into different cell types and in immune cells. These advances are reviewed to provide perspective for future studies.