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A. J. Peterson, R. J. Fairclough and J. F. Smith

Summary. Androstenedione and testosterone were measured by radioimmunoassay after chromatography on micro-columns of Lipidex-5000 in jugular plasma samples taken every 2–3 h at the time of luteolysis and oestrus in 3 dairy cows. The concentrations of androstenedione and testosterone varied between 5 and 60 pg/ml and 5 and 80 pg/ml respectively and no consistent pattern in the fluctuations of either steroid was observed.

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J. F. Smith, R. J. Fairclough and A. J. Peterson

Summary. Plasma concentrations of progesterone and Provera were measured daily in 3 cows during 21 days of treatment with Provera-impregnated intravaginal sponges. Plasma concentrations of oestradiol-17β and 13,14-dihydro-15-keto-prostaglandin F (PGFM) were measured hourly from 5 h before until 62 h after sponge removal. The profile of progesterone concentrations indicated that luteolysis occurred at the expected time (Days 19 to 23 of the cycle), even though plasma Provera concentrations were 150–250 pg/ml. The occurrence of peaks of PGFM after sponge withdrawal suggests that PGF-2α release is stimulated by falling levels of progestagen.

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R. J. Fairclough, J. F. Smith and A. J. Peterson

Previous studies have suggested that the biological activity of steroid hormones can be neutralized by antibodies raised against steroid–protein hormones. Active (Ferin, Zimmering, Lieberman & Vande Wiele, 1968) or passive (Scaramuzzi, 1975) immunization procedures have been reported. The latter method is particularly useful when studying the physiological role of hormones in the oestrous cycle when hormonal changes occur during a relatively short interval.

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R. J. Fairclough, J. F. Smith and L. T. McGowan

Summary. Three cows and 2 sheep were passively immunized against prostaglandin (PG) F on Day 16 and Days 13–15 of the oestrous cycle respectively. The PGF antiplasma was raised in ovariectomized ewes against a PGF-2α–bovine serum albumin complex and showed 100%, 12·5%, 0·3%, <0·05% and <0·01% cross-reactivity with PGF-2α, PGE-2, PGA-2, PGB-2 and arachidonic acid, respectively. Control animals were given an equivalent amount of ovariectomized ewe plasma. In all passively immunized animals there was evidence of a persistent corpus luteum as indicated by plasma progesterone concentrations and the failure of the animals to return to oestrus until at least 29 days after treatment. These data are consistent with previous proposals that PGF-2α is the uterine luteolytic factor in sheep and cattle.

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S. Meier, T. M. Lau, G. Jenkin and R. J. Fairclough

Endometrial oxytocin receptor concentrations and oxytocin-induced plasma concentrations of 13,14,dihydro-15-keto prostaglandin F were investigated on days 14 and 17 of the oestrous cycle and on days 14, 17, 25, 65, 85 and 145 of gestation in ewes. Total 13,14,dihydro-15-keto prostaglandin F release in response to a bolus injection of oxytocin was significantly (P < 0.05) higher at luteolysis (day 17 of the oestrous cycle) than at any other stage of the oestrous cycle or in early gestation. On days 65, 85 and 145 of gestation, total prostaglandin release was significantly (P < 0.05) increased compared with earlier in gestation. Maximum concentrations of 13,14,dihydro-15-keto prostaglandin F in response to oxytocin followed a similar pattern. Oxytocin receptor concentrations reflected total oxytocin-induced 13,14,dihydro-15-keto prostaglandin F release, with increased oxytocin receptor concentrations occurring on day 17 of the oestrous cycle, compared with those observed on day 14 of the oestrous cycle and on days 14, 17 and 25 of gestation. By day 65 of gestation, oxytocin receptor concentrations were again increased. However, on days 85 and 145 of gestation, oxytocin receptor concentrations had decreased to concentrations similar to those observed in early gestation. These results indicate that oxytocin-induced 13,14,dihydro-15-keto prostaglandin F release during early gestation is minimal despite the presence of endometrial oxytocin receptors. In mid-gestation, oxytocin-stimulated 13,14,dihydro-15-keto prostaglandin F release is increased with a concomitant increase in uterine oxytocin receptor concentrations. However, by the later stages of gestation, oxytocin receptor concentrations, but not oxytocin-stimulated 13,14,dihydro-15-keto prostaglandin F release, were again decreased. Thus, there appears to be a dissociation between the response to oxytocin and endometrial oxytocin concentrations at specific stages of the reproductive cycle in sheep.

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D. P. Boshier, R. J. Fairclough and H. Holloway

Summary. Neutral lipids in the maternal uterine caruncular epithelium were studied by histochemical localization with Oil Red O. Results using a scoring system of 1 (negligible lipid) to 5 (maximal lipid) showed that intraepithelial lipid stores were minimal until Days 7–8 of the oestrous cycle and then increased to have a mean score of 4·4 on Days 14–15. In early pregnancy, although relatively high with a mean score of 3·2 at Day 15–16, such neutral lipids were significantly lower than those present at a comparable stage in the oestrous cycle. Thereafter, levels declined to a mean score of 1 on Days 21–23 of pregnancy. Such neutral lipid loss appears to be one of the first signs of the maternal response to the implanting embryo and precedes morphological evidence of transformation of either maternal or fetal tissues.

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T. M. Lau, C. B. Gow and R. J. Fairclough

Summary. Ovariectomized ewes were given progesterone and oestrogen priming as steroid pretreatment and subsequently treated with progesterone, prostaglandin F (PGF), or both. In Expt 1, plasma concentrations of the metabolite 13,14-dihydro-15-keto-PGF (PGFM) were measured after an i.v. injection of oxytocin. There was little PGFM response in the untreated control ewes or in the pretreated ewes. Treatment with PGF alone had no effect (P > 0·05), whereas treatment with progesterone either alone or with PGF significantly (P < 0·05) increased the uterine PGFM response to oxytocin. In Expt 2, chronically ovariectomized ewes had high concentrations of endometrial oxytocin receptors. Treatment with PGF alone did not alter the concentrations of the receptors. Treatment with progesterone either alone or with PGF significantly (P < 0·05) reduced the concentrations of the receptors. It is concluded that progesterone promotes the PGFM response to oxytocin, but simultaneously suppresses the concentrations of endometrial oxytocin receptors.

Keywords: progesterone; PGF; PGFM; oxytocin; receptor; uterus; sheep

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A. J. PETERSON, J. T. HUNTER, R. A. S. WELCH and R. J. FAIRCLOUGH

Ministry of Agriculture and Fisheries, Research Division, Ruakura Agricultural Research Centre, Hamilton, New Zealand

(Received 8th October 1974)

Administration of exogeneous oestrogens, especially when given early in gestation, will terminate pregnancy in the cow (Hill & Pierson, 1958). Normal calving is preceded by a rise of oestrogen levels in the maternal peripheral plasma (Smith, Edgerton, Hafs & Convey, 1973; Robertson, 1974). Although these data suggest that oestrogens may be important in the initiation of parturition, little is known of the source of this oestrogen rise in the cow. It seemed pertinent, therefore, to determine the levels of oestrogens in fetal and maternal plasma over the last 3 weeks of gestation. In the present paper, the levels of free oestrone and oestradiol-17β in the maternal jugular and utero-ovarian vein plasma and in fetal vena cava plasma in relation to the initiation of parturition in the cow were determined by radioimmunoassay.

Catheters

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R. A. Parr, I. F. Davis, R. J. Fairclough and M. A. Miles

Summary. The 330 Merino ewes used in the study were placed with rams at a synchronized oestrus and, on Days 2–14 after mating, the ewes were placed in a feed lot and fed daily a low, medium or high ration (25%, 100% or 200% of maintenance respectively). Progesterone supplement was given to some ewes on Days 8–14 after mating by using a device containing 340 mg progesterone. Blood samples were taken from all ewes on Day 12 for measurement of plasma progesterone concentrations. On Day 14 after mating all ewes were returned to pasture. Pregnancy rate was determined by returns to oestrus and was later confirmed using ultrasound.

There was a decline in the peripheral progesterone concentrations with increasing ration. The pregnancy rate in ewes fed a high ration was significantly reduced when compared with those of ewes fed a medium or low ration (48% vs 68 and 67% respectively; P < 0·05). In ewes fed the high ration exogenous progesterone increased the pregnancy rate from 48 to 76% (P < 0·01). Progesterone treatment did not influence pregnancy rates in ewes fed medium or low rations. The number of fetuses per ewe pregnant was not influenced by level of nutrition or progesterone treatment.

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C. H. Cann, R. J. Fairclough, R. Sutton and C. B. Gow

The temporal variations in endometrial expression of mRNA encoding insulin-like growth factor I (IGF-I) and IGF-II, and insulin-like growth factor-binding protein 1 (IGFBP-1) and IGFBP-2 were investigated between oestrus and day 20 of pregnancy in ewes. Northern blot analysis of endometrial total RNA revealed major transcripts for IGF-I (7.1 kb), IGF-II (5.8 kb), IGFBP-1 (1.3 kb) and IGFBP-2 (1.7 kb). Some minor transcripts for IGF-II were also detected. The low endometrial expression of mRNA encoding IGF-I at day 15 of pregnancy was used as the reference point for time comparison for expression of mRNA encoding IGF-I, IGF-II and IGFBP-2. The mRNA encoding IGFBP-1 was not quantitated since the gene was expressed only on day 15 of pregnancy. Endometrial expression of mRNA encoding IGF-I was increased (P < 0.05) at oestrus and on day 8 of pregnancy relative to expression on day 15, whereas expression of mRNA encoding IGFBP-2 was decreased (P < 0.05). The major IGF-II transcript was unaffected by day of pregnancy. The temporal variation of the expression of mRNAs encoding IGF-I and IGFBP-2 suggests a role for these factors in the uterine environment during early pregnancy in ewes coinciding with rapid development of the embryo and growth of the uterus in preparation for implantation.