Response of human fetal pituitary cells to activin, inhibin, hypophysiotropic and neuroregulatory factors in vitro

Abstract

Activin has been previously demonstrated to directly stimulate the synthesis of GnRH receptors and to increase FSH secretion in non-human pituitary cell cultures (PCC). Several results in Macaque monkeys failed to support an unequivocal role for Inhibin in FSH suppression. Whereas the bioactivity of Inhibin and Activin has been demonstrated in rat PCC, no data exist on human pituitary response to these peptides. We studied, therefore, the secretion of FSH and LH by dispersed human fetal PCC from > 140 midtrimester abortions in response to recombinant human (rh-) Activin-A, Inhibin, and other secretagogues. After mechanical and enzymatic dispersion, using collagenase and deoxyribonuclease, the human fetal pituitary cells were cullured on extracellular matrix (ECM) like material coaled 24 well plate (Primaria, Falcon) in fetal calf serum-containing medium. After 3 days incubation in serum-containing medium, the PCC were washed and preincubated for 90 mins in serum-free medium and incubated with rh-ActivinA, Inhibin, TGF-p, Follistatin, sex steroids, and GnRH in quadruplicate wells. The EC50 of rh-Activin-A for FSH secretion was ~ 10 ng/mL. rh- Activin-A was a more potent secretagogue for FSH secretion than GnRH. On the contrary, GnRH (20 ng/mL) was more potent than rh-Activin A for LH secretion. Nevertheless, a significant increase in LH secretion into the medium was brought about by rh-Activin-A. Inhibin decreased FSH secretion but LH response to Inhibin was inconsistent. GnRH opposed the inhibitory effect of Inhibin on both gonadotropins. In dynamic, short term, repetitive exposure of fetal pituitary fragments to rh-Activin-A (superfusionl we could not receive -a similar increase in LH & FSH as in static incubations, as opposed to a short GnRH exposure. Melatonin did not inhibit LH secretion in human PCC as opposed to rodents. In addition to their endocrine, paracrine, and sutocrine effects and to their role as possible markers, the TGF-b superfamily members may atiect embryogenesis and possibly immunomodulation of the fetus. In contrast to others, who could detect Inhibin-B only in male but not in female fetuses sera, we have measured Inhibin-B in both male and female midtrimester fetal sera, challenging the previous assumption that the fetal origin is only Sertoli cells. Human fetal PCC express the previously reported physiologic responses to Activin and Inhibin generated in non-human experiments on gonadotropin secretion in-vitro, and may serve as a physiologic model for studying human gonadotrope responses to the TGF-b family of peptides. Our preliminary data may provide the first unequivocal evidence for the validity of the Activin/Inhibin hypothesis in human.