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Francesca Stewart and W. R. Allen

Summary. The role of equine chorionic gonadotrophin (CG, formerly termed Pregnant Mare Serum Gonadotrophin, PMSG) in maintaining equine pregnancy was investigated by examining the effects of this hormone on the maternal ovaries during early gestation and relating these findings to the receptor binding activities of CG in vitro. Measurement of plasma progestagen profiles in mares and donkeys carrying horse, donkey, mule (9 horse × ♂ donkey) and hinny ♀ donkey × ♂ horse) conceptuses confirmed that CG induced several secondary ovulations and thus maintained maternal progestagen concentrations. However, in mares carrying horse and mule conceptuses and in donkeys carrying donkey conceptuses the growth of the follicles that gave rise to the secondary corpora lutea occurred before CG was secreted and the CG did not express any FSH-like activity. Nevertheless, in donkeys carrying hinny pregnancies the CG secreted by the hinny conceptus stimulated massive follicular growth in addition to luteinization, presumably because of an enhanced sensitivity of donkey ovaries to hinny CG which, as demonstrated in previous studies, is a mixture of horse and donkey CG and hence has considerably more FSH-like activity than normal donkey CG.

In-vitro receptor binding experiments showed that both horse and donkey gonadal tissues possessed a low binding affinity for horse CG compared to that exhibited by equivalent gonadal tissues of other species. Furthermore, horse CG bound with low, but significant, affinity to horse and donkey LH receptors and donkey FSH receptors, but exhibited negligible binding to horse FSH receptors.

We suggest that in equids the receptor-mediated refractoriness to the gonadotrophic activities of the intraspecific chorionic gonadotrophin protects the ovaries during pregnancy.

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Sandra Wilsher and W R Allen

Eight day 10 horse embryos were transferred non-surgically to recipient mares that had ovulated 7 days after the donors. The embryonic vesicle was seen ultrasonographically in all eight recipients, and three out of eight (38%) of the vesicles developed an embryo proper with a beating heart. Conceptus expansion was initially slower than that in control mares but continued until day 22 (recipient day 15). Time of fixation of the vesicle was related to its diameter, rather than uterine stage. Although the embryo proper first appeared ultrasonographically on day 22, as normal, it grew more slowly and the allantois expanded more slowly than that in control mares with normal pregnancies. The development of endometrial cups and their secretion of equine chorionic gonadotropin in the two mares allowed to remain pregnant to >50 days occurred at a conceptus age ∼7 days later than that in the control mares. The results demonstrated the uniqueness of the horse conceptus in being able to overcome a 7-day asynchrony with the uterus, and also highlighted the overriding influence of the uterine environment on conceptus development in the mare.

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W. R. ALLEN and R. M. MOOR

The gonadotrophin (pmsg) present in the serum of mares between the 40th and 120th days of pregnancy originates in the uterine endometrial cups. These structures begin to develop on the 36th day of pregnancy opposite a transitory, though well-defined, circumferential thickening of the chorion called the allantochorionic girdle (Ewart, 1897; van Niekerk, 1965; Allen, 1970). The endometrial cups are composed of a discrete and densely packed mass of very large, epithelioid, decidual-like cells. They develop before the allantochorion becomes attached to the endometrium and it has been widely accepted in the past that they are exclusively maternal in origin (Clegg, Boda & Cole, 1954; Amoroso, 1955). However, recent genetic evidence, derived from the study of interspecific equine hybrids, has indicated

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W. R. Allen and R. L. Pashen

Summary. The blastomeres of 19 2- to 8-cell embryos recovered surgically 1–3 days after ovulation from 23 Pony mares were mechanically separated and inserted, in various combinations, into evacuated pig zonae pellucidae to make 27 'half' and 17 'quarter' micromanipulated embryos. These were embedded in agar and cultured in vivo in the ligated oviducts of ewes for 3·5–5 days to allow development to the late morula/early blastocyst stage. Subsequent surgical or non-surgical transfer of 13 'half' and 17 'quarter' embryos to mares resulted in 10 established pregnancies, including 2 monozygotic pairs. Surgical transfer to mares that had not been recently used as donors of embryos was more successful (10/20) than surgical or non-surgical transfer to recently operated mares (0/10).

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W. R. ALLEN and L. E. A. ROWSON

Several authors have recently demonstrated the luteolytic action of exogenous prostaglandin F (PGF) in various laboratory and domestic animals and there is now ample evidence that PGF is the uterine luteolytic hormone which terminates the life of the CL in many species (McCracken, 1972; McCracken, Carlson, Glew, Goding, Baird, Gréen & Samuelsson, 1972). In cattle, Rowson, Tervit & Brand (1972) showed that an intrauterine (i/u) infusion of PGF on 2 successive days at any time between the 5th and 16th day of the cycle, induces oestrus 3 days later; they found that for 0·5 mg PGF to be strongly luteolytic in the cow, the substance must be placed in the uterine horn which is ipsilateral to the ovary containing the active CL. This observation is in accordance with the experiments of Moor & Rowson (1966), Harrison, Heap & Linzell (1968) and others, which have indicated

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C. Gerstenberg, W. R. Allen, and F. Stewart

Placentation involves considerable growth and reorganization of both maternal and fetal tissues. In this investigation, immunohistochemical localization of the proliferation marker Ki-67 antigen was used to monitor cell division during placentation in mares. Endometrial biopsies were obtained from eight mares between day 14 and day 26 of pregnancy and from eight anoestrous mares that had been treated with various combinations of progesterone and oestrogen. Samples of endometrium and fetal membranes were obtained from 19 mares carrying normal horse conceptuses between day 30 and day 250 of gestation and from three failing extraspecific donkey-in-horse pregnancies. Proliferation in the superficial strata of the endometrium was increased by day 18 of gestation and this effect could be mimicked by supplementing with oestradiol benzoate during the last 6 days of a prolonged period (18–36 days) of progesterone administration. Fetal chorionic girdle cells were proliferating vigorously at days 30–32 of gestation, but stopped dividing after they invaded the endometrium, while the trophoblast cells of the allantochorion showed an increase in mitotic activity after day 38. The luminal epithelium of the endometrium started to proliferate only after the primary villi of the true epitheliochorial placenta had been formed, and during days 58-70 this effect was seen only in the pregnant horn in which placentation was further advanced. During the second half of gestation, most of the mitotic activity was confined to the periphery of the microcotyledons which were still growing. In the donkey-inhorse pregnancies, proliferation rates of the maternal and fetal epithelia at day 70 of gestation were markedly reduced in areas of heavy endometrial lymphocyte infiltration and poor placentation. These results provide a basis for further studies on factors that influence invasive and non-invasive placentation.

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F J Stansfield and W R Allen

The ovaries of eight African elephant foetuses and their mothers between 2 and 22 months of gestation, and those of two cycling and two lactating elephants, were examined grossly, histologically and immunocytochemically, with emphasis on the development and regression of accessory corpora lutea (CL) of pregnancy and the steroidogenic capacities of the accessory CL and the foetal ovaries. The results supported recent findings that the accessory CL form as a result of luteinisation, with and without ovulation, of medium-sized follicles during the 3-week inter-luteal period of the oestrous cycle. They enlarge significantly and become steroidogenically active around 5 weeks of gestation, probably in response to the placental lactogen which is secreted by the implanting trophoblast of the conceptus. The large luteal cells stained strongly for 3β hydroxysteroid dehydrogenase (3βHSD) activity throughout the 22-month gestation period although they showed vacuolation and other degenerative changes in the final months of gestation coincident with hypertrophy and hyperplasia of 3βHSD-positive interstitial cells in the foetal gonads. It is proposed that the progestagens secreted by the enlarged gonads of the elephant foetus may function both to assist the maternal ovaries in supporting the pregnancy state and to induce torpor and intrauterine immobility of the rapidly growing foetus.

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C. Gerstenberg, W. R. Allen, and F. Stewart

Immunohistochemical detection of the proliferation marker Ki-67 antigen was used to monitor mitotic activity in the endometrium of mares. The monoclonal antibody MIB1 was validated for use on equine tissues by demonstrating its reaction with activated peripheral blood lymphocytes, and endometrial biopsies were recovered from 26 non-pregnant mares at selected stages during the reproductive cycle. The proportion of positively stained nuclei was counted in five random areas on each histological section to determine the percentage and type of proliferating cells. Multiplication rates in the types of cell found in the superficial strata, comprising the luminal epithelium, the epithelium of the gland necks and the stromal cells of the stratum compactum, were greatest during oestrus, presumably under the influence of oestrogens secreted by the growing ovarian follicles. In contrast, the mitotic activity in the cells of the deeper secretory portions of the endometrial glands was restricted to a brief phase between day 3 and day 7 of dioestrus, most likely as a delayed response to the decreasing oestrogen concentrations after ovulation. Some of the degenerate glands in subfertile mares did not follow this pattern of increased epithelial proliferation at that stage. After day 7 of dioestrus, the proliferation rates of cells in the endometrium decreased to basal values and remained low for as long as progesterone concentrations remained evaluated, even during prolonged dioestrus. The technique enabled characterization of normal cell proliferation patterns in the endometrium of mares and it will be a useful tool in the future for monitoring the endometrial responses of reproductively healthy and subfertile mares.

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J. A. Skidmore, W. R. Allen, and R. B. Heap

The ability of the embryonic tissues of the dromedary camel (Camelus dromedarius) to synthesize oestrogens in vitro was studied in 15 conceptuses recovered by non-surgical uterine lavage between 10 and 33 days after ovulation. Definitive evidence for strong aromatase activity with synthesis of considerable quantities of oestrogens was obtained at all stages when conceptus tissues were incubated with [3H]androstenedione. A high proportion of the oestrogens was in the form of oestradiol, which contrasts to the higher ratio of oestrone:oestradiol in the oestrogens synthesized by embryonic tissues of horses and pigs. Biopsies of endometrial tissue recovered from pregnant and nonpregnant camels showed great ability to conjugate both oestradiol and oestrone when incubated with tritium-labelled forms of these two hormones.

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J. E. A. McINTOSH, R. M. MOOR, and W. R. ALLEN

Summary.

The process involved in the disappearance of PMSG from the blood of sheep, following a single intravenous injection, has been separated into two exponential components. Values (mean±S.E.) calculated from experiments on five animals were: metabolic clearance rate (37·8±1·6 ml hr−1); rate constant of disposal (0·0315±0·0016 hr−1); half-time of disposal (21·2±1·1 hr). The stage of the oestrous cycle, ovariectomy and the dose of PMSG used had no apparent effect on these values.