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Summary.

Blastocysts recovered from adult cycling rats on Day 5 of pregnancy had thirty-four nuclei as determined by the squash technique. The nuclei actively incorporated [³H]thymidine in vitro when examined by autoradiography. In delayed-nidation blastocysts on Day 9 of pregnancy, the number of nuclei observed was seventy-four, and a smaller number of nuclei incorporated [³H]thymidine than on Day 5 under identical experimental conditions. Oestrogen and progesterone treatment 30 hr before autopsy of rats with delayed nidation caused stimulation of DNA synthesis in the nuclei of blastocysts before implantation. This was indicated by a greater number of nuclei incorporating [³H]thymidine than in the controls which did not receive oestrogen.

Pregnant mare's serum (pms) is being used by various workers for inducing ovulation in the immature rat (Cole, 1936; Williams, 1945; Zarrow, Caldwell, Hafez & Pincus, 1958; Strauss & Meyer, 1962; McCormack & Meyer, 1962). This report is concerned with the comparison of pmsg preparations manufactured by three different companies as regards their ability to cause ovarian growth and ovulation in the rat. Also, data relating to the effect of storage on the potency of pmsg are described.

The procedure adopted for standardization of different preparations of pmsg by ovarian weight was that of Cartland & Nelson (1938). Twenty-one-day-old female rats were obtained from the Holtzman Company, Madison, Wisconsin and were maintained on Rockland rat and mouse diet and tap water ad libitum. They were housed in an air-conditioned room (78 to 80° F)

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

Summary.

The facilitative effects of certain progestational steroids on ovulation were investigated by using 25-day-old female rats which had been treated on Day 22 with a non-ovulatory dose of PMSG (12 i.u.). Ovulation was caused by treatment with pregnenolone or progesterone on the morning of Day 24. The dose of pregnenolone required was higher than that of progesterone. Progesterone had this effect throughout the morning of Day 24, while prenenolone was only effective between 07.00 and 10.00 hours on Day 24. The two metabolites of progesterone in the hypothalamus and uterus, 5α-dihydroprogesterone and 3α-hydroxy-5α-pregnan-20-one, were also tested for their ability to cause ovulation. Although 5α-dihydroprogesterone possessed this ability, a dose three to four times that of progesterone was required to produce a comparable effect. Doses of up to 1·5 mg 3α-hydroxy-5α-pregnan-20-one were without effect. Neither 17α-hydroxypregnenolone nor 17α-hydroxyprogesterone had any effect in influencing ovulation.

Pregn-5-ene-3,20-dione had a facilitative ability comparable to that of progesterone in doses of 0·25 mg or higher. The facilitative effect of progesterone decreased when it was injected earlier on Day 24 or during the evening of Day 23; no potentiating effect was obtained at 14.00 hours on Day 23. The results obtained with pregnenolone, progesterone and related steroids support the hypothesis that the inhibition of ovulation by phenobarbital may be due in part to its interference with the conversion of pregnenolone to pregn-5-ene-3,20-dione.

Summary.

Progesterone and pregn-5-ene-3,20-dione, the proposed intermediate between pregnenolone and progesterone in the rat ovary, were able to overcome the phenobarbital (PB)-induced block of ovulation in the PMSG-primed immature rats when given 3½ hr after PB.

Pregnenolone failed to cause ovulation in any of the animals treated with phenobarbital, providing support for the hypothesis that the ovulation-inhibiting action of PB may be due in part to its inhibitory action on the step in steroidogenesis between pregnenolone and progesterone.

The principal metabolites of progesterone in the hypothalamus and uterus, 5α-pregnane-3,20-dione and 3α-hydroxy-5α-pregnan-20-one, were not able to overcome the PB-induced block of ovulation. These results suggest that the action of progesterone in overcoming the PB-induced block of ovulation is not because of its transformation to these two compounds.

Summary.

Unilateral ovariectomy on the 3rd day of pregnancy in the rat resulted in arrested embryonic development and decreased implantation in the ipsilateral uterine horn. These degenerative changes were apparent 48 hr, but not 24 hr, after operation. A single subcutaneous injection of either oestrone (1·0 μg) or progesterone (2·0 mg) at 08.00 hours on the 5th day of pregnancy induced implantation and foetal maintenance in the ipsilateral horn. Treatment with progesterone was consistently more effective than oestrogen.

These observations suggest that unilateral ovariectomy induces a hormonal deficiency in the adjacent uterine horn which is incompatible with optimum preimplantation embryonic development.

Summary.

Twelve immature female monkeys were treated with varying amounts of pregnant mare's serum gonadotrophin (pmsg). Seven of these monkeys responded to pmsg treatment as shown by sex skin development, ovarian enlargement and withdrawal bleeding. These animals reached menarche between 23 and 26 months of age, almost 1 year earlier than untreated control monkeys. Five other animals did not show an initial response to pmsg treatment and attained puberty simultaneously with the untreated animals. It is suggested that increased production of oestrogen by the pmsg-stimulated ovaries may affect the hypothalamo-hypophysial axis in such a way that puberty is accelerated.