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J. T. WU

Although Marston & Chang (1965) have noted that the Mongolian gerbil breeds best by monogamous pairing, mating is always unpredictable even when a pro-oestrous female is caged with a male. This causes great difficulty in obtaining a reasonable number of pregnant animals for experimental purposes. The present study was intended to investigate the feasibility of artificial insemination and induction of pseudopregnancy in the Mongolian gerbil in order to obtain a desired number of pregnant animals.

The female Mongolian gerbils of the Worcester Foundation stock and the Tumblebrook Farm stock (West Brookfield, Massachusetts), 2½ to 7 months old, were maintained in animal quarters at 20 to 24°C, under artificial light from 07.00 to 19.00 hours. They were provided with oatmeal, Charles River rat chow and water, supplemented twice weekly with vegetables or apples.

The females usually came into pro-oestrus 2 to 3 days after an intraperitoneal (i.p.) injection of 5 to

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J. T. WU

Rat blastocysts normally shed their zonae pellucidae on Day 5 (Day 1 = spermatozoa in the vaginal smear) between 14.00 and 19.00 hours (Dickmann, 1967). In rats hypophysectomized on Day 1 and treated with various combinations of progesterone and oestrogen, many blastocysts as well as some morulae lose their zonae as early as 09.30 hours on Day 5 (Wu, Dickmann & Johnson, 1971). The cause for such precocious shedding of the zona is not known. Since only a small amount of progesterone is secreted in the first 2 days of pregnancy (Hashimoto, Henricks, Anderson & Melampy, 1968), it seemed possible that the precocious shedding of the zona observed in the previous experiments might result from the progesterone treatment on Days 1 and 2. The present study was designed to determine whether administration of progesterone to intact rats on Days 1 and 2 of pregnancy could cause precocious zona shedding and advance

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J. T. Wu

Summary. The ability of aromatase inhibitors to induce implantation in mice was tested in animals in which implantation was delayed by ovariectomy and progesterone treatment. Implantation was consistently induced by 7 mg 4-hydroxyandrostene-3,17-dione (4-OH-A), 7·5 mg 1,4,6-androstatriene-3,17-dione (ATD) or 15 mg 4-acetoxy-androstene-3,17-dione, an activity comparable to that of 1 mg testosterone. In intact mice treated with 2 or 10 mg 4-OH-A or ATD/day from Day 2 of pregnancy (Day 1 = vaginal plug), the number and size of implantation sites were not affected. These results may not be necessarily due to inhibitory effects of the compounds on aromatase.

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J. T. Wu

Summary. Mouse embryos collected on Days 2 (2-cell) to 4 (early blastocyst) were treated with pronase to digest the zona pellucida and cultured at 37°C for 3 h. These embryos and untreated Day-5 late blastocysts were exposed to [3H]Con A at 25, 50, 100 or 200 μg/ml, 4°C for 30 min, washed and counted for radioactivity. Other groups of embryos were incubated with [3H]Con A in the presence of 0·06 m-αmethyl-d-mannoside for the detection of non-specific binding. Scatchard plot analysis showed that the total number of Con A molecules bound/embryo increased with development, from 12 × 107 in 2-cell embryos to 19 × 107 in early blastocysts and to 150 × 107 in late blastocysts. The association constants decreased from 3 × 106 m −1 in 2-cell embryos to 0·83 × 106 m −1 in late blastocysts. The results suggest that the Con A binding sites (probably glycoproteins) on the embryo surface change quantitatively and qualitatively during preimplantation development.

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J. T. WU and R. K. MEYER

Bacteria can be found in the reproductive tracts of both sexes; some of them are highly spermicidal and may be responsible for infertility (Matthews & Buxton, 1951; Teague, Boyarsky & Glenn, 1971). It has been reported that several viruses can infect and damage implanted mammalian embryos (Sever & London, 1969).

In rabbits, the blastocyst is susceptible to viral and bacterial infections only when implantation has begun (Zimmermann, Gottschewski, Flamm & Kunz, 1963). By contrast mengo-encephalitis virus is capable of infecting, and blocking the further development of, two-cell mouse eggs and morulae in vitro (Gwatkin, 1963, 1967). This communication describes the bacterium-like particles in four rat blastocysts during delayed implantation.

Five 30-day-old female rats of Holtzman strain were induced to ovulate with PMSG (Gonadogen, Upjohn Co.) followed by hcg (International Hormones, Inc.), and were mated with fertile males (Wu & Meyer, 1966). Implantation of blastocysts was prevented by ovariectomy of the

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J. T. Wu and Z. H. Liu

Summary. When mouse morulae, early blastocysts and implanting blastocysts were cultured with tritiated pregnenolone, tritiated progesterone and its metabolites, 5α-pregnan-3,20-dione and 3α-hydroxy-5α-pregnan-20-one, were isolated from the medium. It appears that mouse embryos can make progesterone from pregnenolone and the progesterone is quickly metabolized into various metabolites. These abilities increase with development. It is suggested that the mouse embryo can make progesterone and may regulate its own progesterone level for optimal development.

Keywords: mouse; blastocyst; progesterone formation; pregnenolone; progesterone metabolites

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J. T. Wu and Guey-Meei Lin

Summary. Oestradiol-17β was produced by cultures of 5- and 6-day rabbit blastocysts containing 0·5–1 μm-[3H]testosterone. Addition of the aromatase inhibitor 4-hydroxy-4-androstene-3,17-dione at 3·5–7 um reduced oestradiol production by 66–73% but had no effect on the size of blastocyst. Injection of 6 mg 4-OH-androstenedione or 5–10 mg 4-acetoxy-4-androstene-3,17-dione, into the uterine lumen on Day 5 did not interfere with implantation. The functional significance of blastocyst oestrogen in rabbit remains obscure.

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J. T. WU, Z. DICKMANN, and D C. JOHNSON

Summary.

The beneficial effect of progesterone on blastocyst survival in the uterus was shown in rats hypophysectomized on Day 1 of pregnancy. Treatment with progesterone (2 mg/day) on Day 1, Day 1 and Day 6, or Days 1 to 5 could maintain most blastocysts for only 5 days following the last injection; during the next 5 days, many disintegrated in the uterus. Daily injections of 2 mg progesterone, however, could maintain most blastocysts for as long as Day 53.

In hypophysectomized rats, the developmental potential of blastocysts deteriorated rapidly even though the rats received 2 mg progesterone daily. By Day 20, only 23% of blastocysts were capable of developing into full-term fetuses compared with 52% in rats ovariectomized on Day 4 and injected daily with 2 mg progesterone. By Day 52, none of the blastocysts from either group of animals developed to term although many still retained the ability to implant.