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Z. DICKMANN

Summary.

Rat eggs were transferred to the oviducts of previously mated rabbits. The purpose of such transfers was to find out whether or not spermatozoa of one species can penetrate through the zona pellucida of another species. Of the 673 rat eggs that were examined, the perivitelline space of one contained a rabbit spermatozoon. Penetration in this single instance seemed to have occurred due to abnormalities in the spermatozoon.

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Z. DICKMANN

Summary.

In rats injected with depo-medroxyprogesterone acetate (depo-MPA) at either 10.00 or 22.00 hours on the last day of dioestrus, the anticipated ovulation was blocked; injection at 10.00 hours on the day of pro-oestrus did not block ovulation. When ovulation was blocked, there followed a dioestrous period which lasted, on average, 72·3±1·9 days. Following the prolonged dioestrus, the lengths of the initial cycles were irregular. In most cases, mating did not occur during the first oestrous period. When mating eventually occurred, it was fertile yielding normal offspring. In principle, the results are similar to those obtained for women injected with depo-MPA to effect contraception.

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Z. DICKMANN

Summary.

Pregnant rats were injected subcutaneously with either 1 μg oestrone, 12·5 mg Depo-medroxyprogesterone acetate (MPA), or both. Oestrone injected on Day 3 had no effect on pregnancy. Injection of MPA on Day 1 caused delayed implantation, which was abolished when, in addition, oestrone was injected on Day 4. Injection of MPA on Day 1 followed by oestrone on Day 3 destroyed the eggs during the morula—blastocyst transformation period. The contraceptive effect of the latter treatment suggests a general guide-line for postcoital contraceptive trials in women.

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Z. DICKMANN and R. W. NOYES

Summary.

Previous experiments demonstrated that a particular developmental relationship was critical in determining whether or not rat ova transferred asynchronously into the uteri of recipient rats would survive to term foetuses. The present experiments were designed to determine the fate of transferred ova, particularly at the time of implantation.

Ova that were I day younger than the uterus developed at the usual rate until the 5th day of pregnancy, but then degenerated rapidly and failed to implant. Ova that were 1 day older than the uterus delayed their development and did not implant until the uterus was ready for the implantation interaction. Neither control ova nor ova 1 day older than the uterus could implant on the 4th or 6th days of pregnancy.

It is postulated that in the afternoon of the 5th day of pregnancy, the ovum and the endometrium having independently attained a specific stage of development, the uterine environment suddenly changes, becoming detrimental to younger ova but stimulating to 5-day blastocysts in such a way that they elicit the decidual reaction, become attached to the endometrial epithelium, and begin the process of implantation.

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R. W. NOYES and Z. DICKMANN

Summary.

Eight hundred and fifty-five 2- to 5-day-old ova were transferred from donor rats into the uterine horns of recipient rats on the 2nd through the 6th days of pseudopregnancy. The objective was to establish the lower, optimal and upper limits of development of both ovum and endometrium which were compatible with normal pregnancy. The lower and upper limits of development, 2 and 5 days respectively, proved to be the same for both ovum and endometrium. There was a striking tendency for ova the same age as, or one day older than, the corresponding stage of uterine development to survive more often than ova one day younger than the stage of uterine development. Data previously reported for the rabbit, mouse, and sheep suggest that ovular maturity may be of prime importance to implantation and survival of ova in these species also.

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Z. DICKMANN and SUDHANSU K. DEY

In the rat, two key reproductive phenomena—morula to blastocyst transformation, and implantation—are known to be affected by oestrogen/progesterone changes in the mother. Thus, experimentally imposed hormonal changes can prevent the transformation of morula to blastocyst (Dickmann, 1970, 1973) and delay and induce implantation (Nutting & Meyer, 1963; Mayer 1963). It has been axiomatic that the ovary is the source of oestrogen and progesterone necessary during the preimplantation period. The results of the present study suggest that the preimplantation embryo is an additional, perhaps indispensable, source of steroid hormones which influence the two phenomena mentioned.

Adult virgin female rats of the Holtzman strain, weighing 180 to 220 g, were mated with males of proven fertility. The morning of finding spermatozoa in the vagina was designated Day 1 of pregnancy. On Days 3, 4 and 5, rats were killed and the fertilized eggs were recovered according to the method described by Dickmann

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Z. DICKMANN and V. J. DE FEO

Summary.

It has been reported in the literature that blastocysts during delayed implantation (here referred to as `dormant blastocysts') differ from blastocysts on Day 5 (spermatozoa in vagina = Day 1) of regular pregnancy (here referred to as `active blastocysts') as regards size, mitotic activity and fine structure. In the present study, it was attempted to determine whether these two types of blastocysts also differ in their physiological potential, i.e. whether they can survive under the same environmental conditions. The survivability was tested as follows: `active blastocysts' were transferred into `dormant uteri' (uteri during delayed implantation) and `dormant blastocysts' were transferred into `sensitive uteri' (uteri on Day 5 of pregnancy). In both types of transfers, the blastocysts developed into normal, live foetuses. The compatibility between the uterus and the blastocyst, if one is `active' and the other is `dormant', is discussed.

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S. K. Dey, F. Kimura, A. Mukherjee and Z. Dickmann

Summary. Concentrations of both nucleotides were significantly higher in Day-6 than in Day-5 blastocysts but the ratio of cAMP to cGMP changed from 0·5 to 1·5.

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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.

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Amal Mukherjee, S. K. Dey, Jayasree Sen Gupta, C. S. Ramadoss and Z. Dickmann

Summary. The activities of phosphofructokinase, pyruvate kinase, citrate synthase and creatine kinase were determined in blastocysts from rabbits at 144 h post coitum and in similar blastocysts cultured for 24 h with or without oestradiol-17β (1 μg/ml). There was a significant increase in all the enzymes during the 24-h culture period but oestradiol had no effect.