[Origin and sites of action of inhibin (author's transl)]. / Origine et sites d'action de l'inhibine.

Mice testis in organ culture (31 degrees C) produce a steroid free substance which inhibits FSH secretion by rat pituitary cells. Histologically, Sterloti cells alone remain normal after a few days in culture. A hypothalamic action of inhibin is demonstrated in vitro. The intraglandular content in LHRH is inversely related to the amount of inhibin present in the culture medium. In the testis, DNA synthesis is depended of inhibin. This is demonstrated by studies of the incorporation of tritiated thymidine in testicular DNA in vivo and in vitro. In conclusion, inhibin is produced by Sertoli cells and acts not only at this pituitary level but also on the hypothalamus and the testis.

[Inhibin: new gonadal hormone (author's transl)]. / Inhibine: nouvelle hormone gonadique.

There are many convincing arguments to accept the existence of inhibin. This hormone is produced inside the seminiferous tubules by the Sertoli cells in males and by the granulosa cells of the follicule in females. The biological, immunological and chemical characteristics of testicular and ovarian inhibin are identical so that it could be speculated the same molecule is secreted by both organs. This hormone is not a knownsteroid but is a protein substance. Thus, its biological activity is destroyed by trypsin and pepsin digestion and by heating at 60 degrees for 30 minutes. Furthermore, immunization with inhibin from rete testis fluid induces antibodies capable of neutralizing endogenous inhibin of adult male and female rats. This polypeptide hormone is not identical neither to ABP nor to a fragment of gonadotrophins. The molecular weight is not yet exactly defined and the possibility exists that two forms of inhibin are present in RTF: one of high (greater than 10,000 Daltons) and the other of low molecular weight. The high M.W. species could be a polymer or alternatively the combination of native inhibin and a carrier substance or unique precursor molecule. Inhibin preparations selectively depress the synthesis and the release of FSH in pituitary cell culture. The threshold dose to affect the LH production is higher than that active on FSH secretion. Furthermore, they reduce LH-RH content of hypothalamus maintained in organ culture. In animals, inhibin induced effects are depending on both hypothalamus and pituitary actions according to the functions of these two structures. In that sense, apparently contradictory results are obtained in short and long term castrated animals. Inhibin does not modify TSH, GH and prolactin in vivo and in vitro. This substance displays an inhibition on the synthesis of DNA in the testis of pubertal male rats and depresses the maturation of follicle in female.

Identification in human seminal fluid of an inhibin-like factor which selectively regulates FSH secretion.

Human seminal plasma obtained by centrifugation of human semen contains a factor capable of selectively inhibiting the secretion of FSH both in vivo (reduction of the levels of FSH in rats 24 h after castration) and in vitro (reduction of the FSH released by LH-RH in rat pituitary cell culture). This effect is not due to testosterone, oestradiol-17 beta or progesterone present in the active fractions. The factor has the characteristics of a protein in that its biological activity is destroyed by heat and trypsin digestion. It does not resemble androgen-binding protein. The biological action is not completely specific for FSH as inhibition of LH can be seen with doses usually higher than those which produce inhibition of FSH alone. There is no effect on TSH or prolactin levels in vitro. The factor clearly acts on the release and synthesis of gonadotrophins by gonadotrophs but an effect on the hypothalamus is not excluded. This factor fits the definition of inhibin.

[Incorporation of tritiated thymidine into testicular deoxyribonucleic acid of the rat. Effect of inhibin]. / Etude de l'incorporation de la thymidine tritiée dans l'acide désoxyribonucléique testiculaire du Rat. Influence de l'inhibine.

tritiated thymidine is incorporated into DNA of spermatogonia type B as proved by autohistoradiography when injected in vivo three hours before the sacrifice. Maximum binding and specific activity (labelled thymidine expressed in DPM per mg DNA) are obtained in pubertal rats aged 42 days and weighting 150 g. Inhibin preparation extracted from rete testis fluid (RTF3) specifically inhibits tritiated thymidine into testicular DNA. Thus, no modification of incorporation into hepatic DNA is observed and the preparation loses its inhibitory effect when denatured by heating and trypsin digestion. Tritiated thymidine incorporation into testicular DNA is poor in normal adult rats and in pubertal hypophysectomized animals, RTF3 does not modify the thymidine incorporation in both conditions. The reasons for this lack of effect are discussed. An experimental condition of spermatogonial regeneration is obtained by testicular irradiation. Inhibin preparation inhibits the regenerative DNA synthesis.

[Radioimmunologic assay of alpha-fetoprotein in various normal and pathological conditions]. / Dosage radio-immunologique de l'alpha-foetoprotéine dans différentes conditions normales et pathologiques

AFP can be measured by radioimmunoassay in 52 hours using an incubation at 18 degrees C for 48 hours and the double antibody solid phase method to separate the free labelled AFP from the labelled AFP bound to the antibodies. In these conditions, the sensitivity and precision of the assay are very satisfactory and the results are directly in correlation with the results obtained using the classical double antibody method. In the serum of normal people, except pregnant women, the concentration of AFP is not detectable or is less than 20 ng/ml. In the serum of pregnant women, AFP increases from the 8th. week of gestation to the 32nd., then stabilises or gradually decreases.