The multicentric study regroups 128 cases of the ovarian hyperstimulation syndrome (OHSS) in in-vitro fertilization (IVF) and 256 selected controls. Values of serum oestradiol obtained from different laboratories were found to be normally distributed after logarithmic transformation. Comparative study of clinical and biological characteristics indicates that among OHSS patients (i) mean age was lower; (ii) tubal indications for IVF were less frequent; (iii) polycystic ovary-like conditions (i.e. hyperandrogenism, anovulation, luteinizing hormone/follicle stimulating hormone ratio > 2) were more frequent. OHSS patients displayed ovarian hypersensitivity reflected by higher oestradiol peak concentrations in response to lower dosage of human menopausal gonadotrophin and by a steeper slope of oestradiol increment during stimulation. In these patients, the collection of greater numbers of fertilizable oocytes allowed replacement of more embryos with a good vitality score. Ongoing pregnancy rate was found to be higher among the OHSS patients. The following complications were recorded among OHSS cases: abdominal fluid at echographic examination or clinical ascites (86.7 and 71.1%, respectively); pleural and pericardial effusion (21 and 3%, respectively); haemoconcentration (71.1%); electrolytic disorders (6.2%). Although significantly different between groups, clinical and biological parameters under study showed considerable overlap of their distributions in control and OHSS cases. Therefore, these data must be submitted to discriminant analysis in order to derive a formula predictive of the risk of OHSS.

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Inhibin extracted from human seminal plasma and from rete testis fluid is a protein substance. Two forms of inhibin exist in RTF and each has a different molecular weight. The species of higher molecular weight systematically yields a product of lower molecular weight during chromatography. This phenomenon could represent depolymerization of the molecule, an associated transport protein or alternatively a precursor form of inhibin. The inhibin preparations utilized selectively lowered the levels of FSH as assessed both in vivo and in vitro. This action was not totally specific since increasing doses of inhibin also produced a lowering of the levels of LH. In contrast, these preparations did not influence the secretion of TSH, growth hormone or prolactin in vivo or in vitro. A direct effect of inhibin on pituitary cells has been clearly established by demonstrating a reduction in the release of FSH in response to GnRH and its synthesis in the pituitary cells. Additional direct effects on the hypothalamus and on gametogenesis in the testis remain to be excluded. On the basis of selective effects of inhibin on FSH secretion, one could envisage the utilization of this hormone as an antifertility agent.

Abstract. When injected in vivo 3 h before sacrifice or when incubated in vitro with testicular fragments for 3 h, tritiated thymidine, a reliable index of DNA synthesis and of mitotic activity, was incorporated into the DNA of differentiated spermatogonia, as shown by autohistoradiography. The maximum DNA specific activity was obtained in pubertal rats aged 42 days, weight 150 g. Two preparations of inhibin extracted from ram rete testis fluid (RTF) of different molecular weight (> 10 000 for RTF1 and < 5000 for RTF3) but which possess the same biological properties were investigated for their effect on thymidine uptake in vivo and in vitro. In vivo both preparations specifically inhibited tritiated thymidine incorporation into testicular DNA of pubertal animals (42 days). No change in thymidine uptake into hepatic DNA was observed. Tritiated thymidine incorporation into testicular DNA was lower in normal adult rats and in hypophysectomized pubertal animals. RTF1 and RTF3 did not affect thymidine incorporation in either case. The reasons for this lack of effect are discussed. In vitro, both preparations induced a dose-dependent decrease in DNA synthesis in testis fragments from rats aged 42 and 49 days. The preparations lost their in vivo and in vitro inhibitory effects when denatured by heating and trypsin digestion. The inhibin preparations probably reduced testicular DNA synthesis and spermatogonial multiplication by reducing FSH secretion in vivo but also had a direct effect on the germ cells as shown by the in vitro experiments. These in vivo and in vitro actions of inhibin preparations are similar to those of the testicular chalones. The relationship which might exist between inhibin and the chalones is discussed.

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