Inhibin and follistatin concentrations in fetal tissues and fluids during gestation in sheep: evidence for activin in amniotic fluid

Abstract

The concentrations of inhibin and follistatin in amniotic fluid and in tissue extracts from the placenta, gonads and adrenals of fetal sheep were measured using radioimmunoassays. These tissue extracts were from whole fetuses from days 16 to 45 and from the individual organs from day 46 to 145 (term) and were assayed at multiple dilutions. The capacity of these extracts to alter FSH production of rat anterior pituitary cells in culture was also assessed at multiple dilutions. Immunoactive inhibin concentrations in amniotic fluid from both sexes increased during gestation and levels were significantly greater in males than females. Peak concentrations of immunoreactive inhibin of 11.2 +/- 1.9 ng/ml were found in males at 116-125 days of gestation. Follistatin concentrations did not change throughout gestation and no significant difference was noted between sexes. Mean follistatin levels throughout gestation were 3.0 +/- 0.9 ng/ml for males and 3.7 +/- 0.9 ng/ml for females. Despite the potential for FSH inhibition by inhibin and follistatin, amniotic fluid from both sexes at all stages of gestation stimulated FSH secretion in the pituitary cell bioassays, suggesting the presence of activin which was confirmed by the measurement of immunoactive activin (13.3 +/- 2.5 ng/ml) in a specific radioimmunoassay. Maximum concentrations of immunoactive and bioactive inhibin in placental extracts were observed in late gestation (2.2 +/- 0.6 and 3.8 +/- 1.6 ng/g respectively) and there was no significant difference between sexes. Follistatin concentrations in placental cotyledons ranged from 11.5 to 27.1 ng/g with no significant difference between sexes. In view of the higher follistatin concentrations compared with inhibin, it is likely that the capacity of placental extracts to suppress FSH production by pituitary cells in culture is due predominantly to follistatin. Immunoactive inhibin was observed in high concentrations in the fetal testis throughout gestation; with concentrations increasing to a maximum of 1993.0 +/- 519.7 ng/g at 126-135 days of gestation with a ratio of bioactive: immunoactive inhibin of 1:20. Although bioactive and immunoactive inhibin was also observed in fetal ovaries and adrenals from both male and female fetuses, concentrations were lower than those observed in fetal testes. Follistatin concentrations in the fetal testis were elevated between 70 and 95 days (97.6 ng/g) and then declined. Similar concentrations were found in the adrenal glands of both sexes (males 83.5-103.3 ng/g: females 55.3-95.8 ng/g).(ABSTRACT TRUNCATED AT 400 WORDS)

Source of Inhibin in Ovine Fetal Plasma and Amniotic Fluid during Late Gestation: Half-Life of Fetal Inhibin1

“…In contrast to the elevated concentrations observed in maternal plasma during pregnancy in the human, concentrations of ir-inhibin in the maternal plasma of the ewe are not elevated during late gestation apart from a transient rise observed at the time of parturition [4]. In this species the placenta does not appear to be a major source of inhibin since, although both bioactive and immunoactive forms of inhibin have been detected in the placenta during gestation [5], uninuclear trophoblast cells in culture produce only minimal amounts of inhibin [6], and there is no significant arteriovenous difference in ir-inhibin concentrations across the placenta in chronically cannulated late-pregnant sheep [7]. During pregnancy in both the human and sheep, no difference has been found in maternal plasma inhibin concentrations in individuals carrying male versus female fetuses [4,8].…”

“…Both immunoactive and bioactive inhibin have been observed in high concentrations in ovine fetal testes throughout gestation [5]. Although bioactive and immunoactive inhibin were also observed in fetal ovaries and adrenals from both male and female fetuses, concentrations were lower than those observed in fetal testes.…”

“…Although bioactive and immunoactive inhibin were also observed in fetal ovaries and adrenals from both male and female fetuses, concentrations were lower than those observed in fetal testes. Elevated concentrations of ir-inhibin have also been observed in amniotic fluid of ovine fetuses during late gestation [5]. The concentrations in amniotic fluid of ovine female fetuses were significantly less than in male fetuses but greater than those observed in maternal plasma [6].…”

Ovine Allantoic Fluid Contains High Concentrations of Activin A: Partial Dissociation of Immunoactivity and Bioactivity1

“…We have previously shown that amniotic fluid from sheep contains predominantly activin bioactivity despite the fact that it contains elevated levels of immunoactive inhibin [9], and we subsequently isolated activin A [10] from a pool of this fluid. The placenta, fetal membranes, and maternal decidua have been shown to be sources of activin in human pregnancy [11][12][13][14], and there are preliminary data to suggest that activin A may be involved in parturition in humans [15].…”

“…It has also been demonstrated that both activin ␤ A and ␤ B subunits are expressed in the amnion and chorion of humans [13]. Since we had previously shown that activin bioactivity was present in amniotic fluid, despite its high levels of immunoactive inhibin activity [9], and we were able to subsequently isolate activin A from amniotic fluid [10], we decided to investigate whether allantoic fluid also contained activin.…”