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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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R. W. NOYES, L. L. DOYLE and D. L. BENTLEY

Summary.

Eighty of 640 4-day and 5-day ova transferred into the uterine horns of two strains of rats on Day 4 of pseudopregnancy developed into foetuses that were weighed on Day 18 of pregnancy. The foetuses developing from 5-day ova weighed significantly more than those resulting from 4-day ova. Analysis of three other factors contributing to foetal weight showed that none of these differed significantly from zero. One additional day of development before implantation gives ova a selective advantage over normally developed controls in terms of foetal weight at term. Further experiments are in progress to study this effect in more detail, and in other species.

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J. C. HSIA, L. H. PIETTE and R. W. NOYES

Success in studying the rate of flow of spermatozoa through the female reproductive tract in vivo will require a sperm-labelling method better than those at present available. Radiophosphorous labelling in vivo (Ortavant, 1954), and radio-active amino acid labelling in vitro (Bhargava, 1957) do not yield specific activities high enough for detection in vivo. Fluorescence labelling cannot be detected in vivo (Ericsson, 1967). Partial success has been obtained by binding spermatozoa to 131I-labelled anti-sperm antibody in vitro, but this label is slowly lost from the spermatozoa in the female tract (Noyes, 1968, 1969). A surface active label has been designed which can intercalate itself between the lipid bilayers or the lipoprotein fraction of plasma membranes (Hsia & Piette, unpublished). The present report is a preliminary account of the adaptation of this labelling method to rabbit spermatozoa in vitro. Lauric, myristic and stearic fatty acid spin labels with the following