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Y Akazome, T Abe and T Mori

The gonad is an endocrine organ secreting sex hormones and also a target of pituitary gonadotrophins. The expression of mRNAs encoding LH receptor (LHR), FSH receptor (FSHR), P450c17 and P450aromatase in the developing gonads of embryos between day 4 and day 6 of incubation was determined using a RT-PCR to elucidate the chicken gonad as a target organ of gonadotrophins. Although expression of mRNAs encoding LHR, FSHR and P450c17 was detected at day 4 of incubation in both sexes, mRNA encoding P450aromatase appeared at day 6 in female embryos only, indicating that mRNAs encoding gonadotrophin receptors can be identified before sexual differentiation. Quantitative PCR analysis revealed that expression of mRNA encoding LHR and FSHR remained low in male gonads from day 4 to day 6 of incubation, whereas they increased on day 6 in female gonads. The sexual dimorphism in the expression of mRNAs encoding LHR and FSHR was confirmed in the sexually differentiated gonads of embryos at day 12 of incubation (LHR in ovary ratio LHR in testis = 7 ratio 1; FSHR in ovary ratio FSHR in testis = 9 ratio 1).

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K. Abe, H. Takano and T. Ito

Summary. Different parts of the epididymal duct were ligated when mice were 90 days old. The mice were killed 1–4 weeks later. PAS-positive materials appeared in the epithelial cells of Segment IV (corpus epididymidis) after ligation of the efferent ducts or at Segment II (middle part of caput) but not when the ligature was distal to Segment II. The inclusions were seen as early as 1 week after ligation and became increased in size and number with time.

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H. Abe, T. Satoh and H. Hoshi

The effects of steroid hormones (oestradiol and progesterone) on the appearance of a golden hamster oviduct-specific glycoprotein (GHOGP) in the epithelium of the oviduct of the newborn golden hamster were investigated by immunoblotting and immunohistochemical staining with a GHOGP-specific monoclonal antibody. Newborn golden hamsters (1.5 days old) were injected daily with oestradiol (1 μg) or progesterone (10 μg). An oviductal extract of oestradiol-treated golden hamsters for 4 days apparently immunoreacted with the monoclonal antibody on a broad band with a molecular mass of more than 200 kDa by immunoblotting under reducing conditions. This broad band was consistent with the migration of GHOGP in an extract of adult oviducts. Consecutive daily injections of oestradiol induced the appearance of GHOGP in undifferentiated epithelial cells of the oviduct of neonates. In oviducts of oestradiol-injected animals, GHOGP was first detected in the Golgi region and then increased in amount to fill the supranuclear cytoplasm of the epithelial cells. The inductive effect of oestradiol was dose-dependent. In contrast, consecutive daily injections of progesterone had no effect on the appearance of GHOGP in the oviductal epithelium. The effects of oestradiol and progesterone in organ culture of oviducts were examined in vitro, by culturing oviductal organs from 1.5-day-old newborn golden hamsters in chemically defined medium supplemented with oestradiol or progesterone for 2 days and then subjected to immunohistochemical staining. The immunoreaction was detected only in the epithelial cells of oestradiol-treated oviducts at concentrations of > 0.01 ng ml−1, but not in the cells of untreated and progesterone-treated oviducts. These results indicate that the production of GHOGP in the epithelial cells of the oviduct of newborn golden hamsters is induced by oestradiol both in vivo and in vitro. It is suggested that oestradiol may be involved in the synthesis of GHOGP in the oviduct during postnatal development of golden hamsters.

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N. Murakami, T. Abe, M. Yokoyama, A. Katsume, H. Kuroda and T. Etoh

Summary. In Sprague–Dawley rats kept under 14L:10D (lights on 05:00–19:00 h), parturition occurred during the light phase on Day 23, and the pre-partum decrease in progesterone concentrations was observed between 07:00 and 15:00 h during the light period on Day 22. When the rats were transferred to reversed light–dark regimen (lights on 17:00–07:00 h) on Day 7, the progesterone decrease and parturition still occurred during the light period on Day 21 and 22–23, respectively. However, when rats were kept in constant darkness from Day 7, parturition occurred independently of the time of day between Day 22 and 24. A gradual decline of progesterone concentrations was randomly observed in individual rats. In Wistar rats kept under the usual light–dark regimen, parturitions were biphasic, occurring during the light periods on Day 22 and 23. The progesterone decrease occurred at the usual time even when the lighting regimen was changed only on the day of the expected progesterone decrease. However, treatment with pentobarbitone sodium at 15:00, 19:00 or 21:00 h, but not at 12:00 or 23:00 h, on Day 21 resulted in a delay of progesterone decrease and of parturition. Complete lesion of the suprachiasmatic nucleus on Day 13 or 14 led to advancement and random distribution of the time of birth.

These results suggest that the time of parturition and of pre-partum progesterone decrease may be closely associated with an endogenous circadian system, and a luteolytic factor involving the nervous system may be present during a limited period before parturition.