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A. PSYCHOYOS and P. MANDON

Delayed implantation can be experimentally induced in the rat by various procedures postponing the completion of the progesterone-oestrogen sequence which results in the uterine state of receptivity (Psychoyos, 1967). Thus, in animals ovariectomized early in pregnancy and treated subsequently with progesterone alone, the uterus remains in a 'neutral' state which can be extended to several months, until oestrogen is added to the progesterone treatment. The present paper reports observations obtained by scanning electron stereoscopy on the ultrastructure of the surface of the luminal epithelium during this state.

The endometria used for this study were taken from Wistar-strain rats ovariectomized on the 2nd day of pregnancy and treated daily with 5 mg of progesterone. On the 10th to 12th day post coitum, laparotomies were performed under ether anaesthesia

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A. Psychoyos and I. Prapas

Summary. RU 486 was administered to rats on Day 1 or Days 1 + 2 of pregnancy. Endometrial sensitivity (i.e. decidualization in response to oil instillation) was delayed by 2·5 mg/kg injected s.c. on Day 1, and almost half of the animals also exhibited a delay in implantation of 1–2 days. Higher doses (5 or 10 mg/kg) administered on Days 1 + 2 reduced the number of implantations to zero in all animals. Apparently normal morulae were found up to the evening of Day 4 in the oviduct and/or the uterus of most animals. However, on the morning of Day 5, ova were detected in only 25% of the animals and all were in the uterus: none was at the blastocyst stage and they appeared to be degenerated or compacted morulae. Egg survival and rate of egg recovery from the uterus was not improved by early ovariectomy, showing that this antiprogestagen acts on these events independently of the presence of circulating oestrogens.

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N. SANANES and A. PSYCHOYOS

Summary.

The cellular localization of uterine adenyl cyclase in rats was demonstrated at the ultrastructural level by a cytochemical technique. Following ovariectomy, oestradiol was shown to induce a high level of adenyl cyclase activity on the apical plasma membrane of the luminal epithelial cells. This oestradiol effect was strongly reduced by pretreatment with progesterone.

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J. Bernard and A. Psychoyos

Follicular fluid, the composition of which has been shown to be nearly the same as that of plasma, contains many substances believed to be secreted by the thecal and/or granulosa cells, e.g. steroids, particularly oestradiol-17β and progesterone (Short, 1962), pituitary hormones (McNatty, Hunter, McNeilly & Sawers, 1975) and mucopolysaccharides (Zachariae & Jensen, 1958). The proteins in follicular fluid are the same as those of plasma, although of different concentrations (Desjardins, Kirton & Hafs, 1966; Shalgi, Kraicer, Rimon, Pinto & Soferman, 1973; Menezo & Testart, 1975). Follicular fluid is probably, therefore, only partly a transudate from the plasma; its role in follicular growth and ovulation has been discussed extensively by Edwards (1974). Although no specific antigenic substance in follicular fluid has yet been demonstrated, it has been suggested that granulosa cell luteinization is controlled by an inhibitory factor in the fluid (El-Fouly, Cook, Nekola & Nalbandov, 1970; Channing, 1973) and Moore et al. (1975) found an inhibition of the activity of RNA-polymerase of rat Yoshida ascites cells by bovine follicular fluid. Bernard (1975) showed that pig follicular fluid prevents morphological differentiation of rat granulosa cells in vitro, but does not alter their progesterone secretion. To investigate further the presence and nature of a 'luteinization inhibiting factor' in follicular fluid we compared the incorporation of [3H]uridine into the total RNA by rat granulosa cells after incubation in either serum or bovine follicular fluid.

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Dominique Martel and A. Psychoyos

Summary. Rats were ovariectomized for 3 weeks and then treated for 3 days with 4 mg progesterone. The cytosolic oestradiol receptor content in the stroma cells was very high (∼21 000 binding sites/cell) as compared with that in the epithelial cells (∼3000 binding sites/cell). The nuclear receptor values were low (∼500 binding sites/cell) in both types of cell.

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N. C. Rath and A. Psychoyos

When implantation is experimentally delayed, blastocyst growth and mitotic and metabolic activities cease. A single administration of oestrogen in vivo activates the metabolic processes which culminate in implantation of the blastocysts (Prasad, Dass & Mohla, 1968; Psychoyos, 1973,1974; Holmes & Dickson, 1975). Metabolic activation of 'delayed' blastocysts can also be induced by culturing them in media containing fetal calf serum (Psychoyos & Bitton-Casimiri, 1969; Psychoyos, 1969, 1973, 1974; Weitlauf, 1974a, b; Psychoyos, Bitton-Casimiri & Brun, 1975). Two explanations of the mechanism of embryonic dormancy and activation have been suggested: (1) the uterine environment may be suboptimal because of the absence of an essential component, the replacement of which results in activation; and (2) dormancy may be induced by a 'repressive factor' of uterine origin, the removal of which causes activation (Psychoyos, 1973, 1974; Psychoyos et al., 1975). The present experiments on the activation of DNA synthesis in the 'delayed' blastocyst in vitro were undertaken to study these possibilities.

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J. L. BRUN and A. PSYCHOYOS

Exposure of mouse blastocysts in vitro to acidified media effective in dissolving the zona pellucida (Gwatkin, 1964), was reported to be incompatible with the survival of the blastocyst (Bowman & McLaren, 1969). It has been concluded that decreased pH is unlikely to be responsible for the lysis of the zona pellucida in utero (Bowman & McLaren, 1970). This conclusion was drawn from data concerning the effect of a prolonged exposure (up to several hours) of eggs to acidity in vitro. Evidence is reported here to show that the dissolution of the zona pellucida by a brief exposure of the blastocyst to acidity is compatible with its viability and subsequent development.

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F. C. CHRÉTIEN, J. COHEN and A. PSYCHOYOS

In primates, ruminants and some rodents, the semen is not ejaculated directly into the uterus but is deposited in the vagina. Mucus is elaborated and secreted in the upper part of the cervical canal in these species, and the canal can reasonably be supposed, therefore, to act both as a reservoir in which the spermatozoa are stored after copulation and as a selective cyclic filter, allowing the spermatozoa to enter the uterus only during the ovulatory period.

The theoretical spatial organization of human mucus micelles has been studied using the technique of nuclear magnetic resonance (Odeblad, 1968). Organized as a network of fibrils linked together by oblique or transverse bonds, the micelles show a "tricot-like macromolecular arrangement". During the ovulatory period, the meshes would enlarge in order to let the sperm cells penetrate and permit their migration towards the uterine cavity. During the luteal phase, the glycoprotein chains which constitute

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V. BITTON-CASIMIRI, J. L. BRUN and A. PSYCHOYOS

Summary.

Rat blastocysts, flushed from the uterus at the moment of the initiation of the implantation process and observed in vitro by time-lapse cinematography, were seen to undergo a series of contractions and dilatations. By these movements, vesicles, containing granular material, emerged through the zona pellucida into the culture medium.

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V. Bitton-Casimiri, J. L. Brun and A. Psychoyos

Laboratoire de Physiologie de la Reproduction, CNRS, E.R. 122, Hôpital de Bicêtre (INSERM), 94270 Bicêtre, France