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R. SAUNDERSON and P. J. HEALD

It is well established (Tabor & Tabor, 1972) that tissues undergoing rapid growth and differentiation exhibit increased levels of ornithine decarboxylase [E.C. 4.1.1.17]. In reproductive tissues, ornithine decarboxylase (ODC) activity is elevated following a response to hormones, as in the oestrogen-treated chick oviduct (Cohen, O'Malley & Stasty, 1970), the uterus of the oestrogen-treated castrated or prepubertal rat (Kaye, Icekson & Lindner, 1971; Russel & Taylor, 1971), and in the prostate gland of the testosterone-treated castrated rat (Williams-Ashman, Pegg & Lockwood, 1969).

The enzyme activity in the uterus of the cycling rat has been closely associated with the levels of circulating oestrogens since it has been shown (Kaye et al., 1971; Hernandez, Ballesteros, Mendez & Rosado, 1973) that ODC activity is maximal at pro-oestrus but is very low or absent at oestrus, and remains low

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J. E. O'GRADY and P. J. HEALD

Summary.

A study has been made of the distribution and spacing of implantation sites in the uterus of the rat at the 5th day of pregnancy. It has been shown that, whereas the implantation sites along the horns are distributed in an entirely random manner, the distances between the sites are significantly non-random. These results are similar to those previously described for the rabbit and the mouse, and rule out the possibility of predicting a site of incipient implantation in the uterus of the rat.

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R. J. REID and P. J. HEALD

Summary.

The uptake of [3H]leucine into total uterine protein of the 5-day cycling rat has been examined during the oestrous cycle, early pregnancy and pseudopregnancy and in animals receiving an antiimplantation compound, ICI 46,474.

It has been shown that uptake in the oestrous cycle is maximal at dioestrus and minimal at oestrus, an event which is out of phase with the known times of maximal oestrogen release. In the pseudopregnant rat, maximal protein synthesis occurred on Days 3 and 4, the uptake on Days 5 to 8 being the same lowered values as on Day 1. Consideration of this result in relation to changes in the oestrous cycle leads to the conclusion that the stimulated uptake is not due to oestrogen acting alone. In the pregnant rat, protein synthesis is markedly stimulated by the morning of Day 5 (10.00 hours). Comparing this with results in the pseudopregnant rat, it is concluded that the increased protein synthesis is indicative of the commencement of early decidualization which, by this measure, is well advanced at the time of experimentation. It has further been shown that an implantation-inhibiting dose of ICI 46,474 results in a pattern of protein synthesis similar to that found in pseudopregnancy. Examination of this, together with previous data, suggests that ICI 46,474 may suppress the protein synthesis which normally occurs on Day 5 of pregnancy.

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J. S. MAJOR and P. J. HEALD

Summary.

The effects of the non-steroidal, postcoital, antifertility agent, ICI 46,474, on ovum transport and implantation in the rat have been examined. When administered as a single implantation-inhibiting dose on Day 2 of pregnancy, the compound had only a marginal effect on the transport of ova through the oviduct. After entering the uterus at approximately the normal time, however, 79 % of the eggs were lost by Day 6. The remaining eggs, while unimplanted, had shed their zonae pellucidae. When animals were treated on Day 2 of pregnancy with a dose of ICI 46,474 which reduced the size of implantation sites observed on Day 9, but which allowed pregnancy to occur, implantation was delayed by some 16 hr. It is concluded that ICI 46,474 given on Day 2 of pregnancy is capable of affecting implantation without altering blastocyst transport through the oviduct and it is suggested that alteration of uterine metabolism is the main factor contributing to its antifertility effects in the rats used.

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U. A. Siddiqui and P. J. Heald

Summary.

Mature female rats were given U11,555A and U11,100A orally on Day 2 of pregnancy and the number of implantations counted on Day 9. Using doses which reduced the implantation number to approximately 40 % that of the controls, it was shown that the reduced number was not due to an effect on egg transport or to a delay of implantation.

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P. J. HEALD, J. E. O'GRADY and A. J. HOWIE

Summary.

Changes in levels of RNA and DNA in rat uterus have been measured throughout the oestrous cycle in two strains of rats by a method designed specifically for application to uterine tissue. It has been shown that there are significant cyclic variations of RNA and DNA, dry matter and water content, but none in total nitrogen in the uteri of Sprague-Dawley rats with a 5-day cycle, and no significant changes, except in RNA, in the uteri of a Wistar strain with a 4-day cycle. In the Sprague-Dawley rats, RNA/DNA ratios were highest in pro-oestrus and oestrus, and lowest in di-oestrus, the increase in RNA/cell preceding the period of maximum growth and total nitrogen content in the uterus during the cycle.

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S. C. Bell, Sheila Reynolds and P. J. Heald

Summary. The synthesis of uterine-soluble proteins during early pregnancy in the rat has been examined by means of dual-isotope labelling techniques and subsequent electrophoretic analysis. A protein of similar electrophoretic mobility to the uterine oestrogen-induced protein was observed, and synthesis of this 'presumptive induced protein' was maximal on Day 4 and Day 6 of pregnancy but low on Day 5. Pregnancy-associated protein synthesis was observed in many regions on polyacrylamide gels, including the β-lipoprotein, α2-macroglobulin, post-transferrin and albumin regions. Synthesis of the post-transferrin species rapidly increased from Day 4 to reach a maximum on Day 6 in the implantation tissue. The temporal pattern of synthesis of post-transferrin protein and of 'presumptive induced protein' suggests involvement in the processes of cell proliferation and decidualization.

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P. J. HEALD, J. E. O'GRADY, ANNE O'HARE and MAUREEN VASS

Summary.

The uptake of [5-3H]uridine into RNA and DNA of the cells of the uterine luminal epithelium, stroma and myometrium of the rat has been studied in early pregnancy using a technique for separation of the cell fractions before quantitative analysis. Comparisons of the metabolism between the pregnant and pseudopregnant horn of the unilaterally ovariectomized rat has shown that RNA and DNA synthesis are markedly increased by 04.00 hours on the morning of Day 5 in the pregnant horn. This increased metabolism occurs in all cell fractions and before the zona pellucida is shed. The results are discussed in relation to the onset of the decidual response.

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P. J. HEALD, A. D. T. GOVAN and J. E. O'GRADY

Summary.

An apparatus and procedure is described permitting the ready separation of luminal epithelial and stromal cells (together with the glands) from the rat uterus.