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R. K. W. Smith and M. H. Johnson

Summary. The third (4-cell) and fourth (8-cell) cell cycles of early mouse development have been analysed in populations of blastomeres synchronized to the preceding cleavage division. DNA content was measured microdensitometrically. The entry of blastomeres into these cell cycles showed considerable heterogeneity both within and between individual embryos. This heterogeneity was greater in the fourth than in the third cell cycle. The component phases of the third cell cycle were estimated as G, = 1 h, S = 7 h, and G2 + M = 2–5 h, and those of the fourth cell cycle as G1 = 2 h, S = 7 h, and G2 + M = 1–3 h.

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S. K. Smith and R. W. Kelly

Summary. Synthetic platelet-activating factor (PAF-acether, 1-0-alkyl-2-acetylsn-glycero-3-phosphocholine) caused a dose-dependent increase in the synthesis of prostaglandin (PG) E-2 by an enriched glandular, but not stromal, fraction of human endometrium removed in the secretory phase of the menstrual cycle. PAF-acether did not alter the synthesis of PGF-2α by this fraction and consequently there was a significant reduction in the ratio of the amounts of PGF-2α/PGE-2 released by the cells into the culture medium. The preimplantation human embryo secretes PAF, and these findings may have relevance to the local maternal recognition of pregnancy.

Keywords: endometrium; platelet activating factor; prostaglandin; implantation; human

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R. N. Kirkwood, K. R. Lapwood, W. C. Smith, K. Moller, and D. J. Garrick

Summary. Forty-two Landrace × Large White sows were used in 3 studies of oestradiol benzoate treatment 24 h (E1) or 48 h (E2) after piglet removal, following lactations of 10 (S) or 35 (L) days, or were untreated controls (C). For Exp. 1, oestradiol benzoate doses were 4, 16 and 64 μg/kg body weight; since highest mean LH peaks followed use of the 16 μg/kg dose, this treatment was used in later studies. Treatments for Exp. 2 were S-E1 and L-E1 (N = 3). Pregnancy rates were 1/3 and 2/3, respectively, while 10-day weaned sows tended to have longer weaning—remating intervals, shorter oestrous periods and lower post-injection oestradiol peaks. Post-treatment LH peaks were recorded from all L-E1 sows, but only one S-E1 animal. Treatments S-E2, L-E2, S-C and L-C (N = 6) were used in Exp. 3; pregnancy rates were 1/6, 6/6, 5/6 and 6/6, respectively, while peak oestradiol levels were 49·5 ± 8·3, 74·8 ± 15·1, 21·7 ± 2·0 and 51·8 ± 26·5 pg/ml, respectively. Weaning—remating intervals were extended in S-C sows (P < 0·05), while oestradiol treatment prolonged behavioural oestrus. LH peak values were reduced after short lactations, but not affected by oestradiol treatment. Plasma prolactin concentrations at weaning were higher in sows in treatment S than in treatment L, while at the subsequent oestrus in oestradiol-treated sows they were elevated more and for longer periods than in controls. These results demonstrate that reduced gonadotrophin secretion and fertility after short lactations are not overcome by treatment with oestradiol benzoate.

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R. N. Kirkwood, K. R. Lapwood, W. C. Smith, and I. L. Anderson

Summary. Piglets were weaned from multiparous sows at 10 days (Group E; N = 7) or 35 days (Group C; N = 8) of lactation. Blood samples were collected at 8 h intervals from the day before weaning (Day – 1) until and including the day of first mating, then once daily until 10 days post coitum. Additionally, 5 sows in each group were sampled at 30 min intervals for 12 h on Days – 1, 0 and 1, then at 30 min intervals for 6 h daily until mating, finally at 30 min intervals for 2 h daily until 5 days post coitum. Group E sows had relatively longer weaning to remating intervals (8·3 ± 0·8 compared with 5·0 ± 0·7 days; P < 0·01) and tended, but not significantly, to produce smaller subsequent litters (10·2 ± 1·9 compared with 12·0 ± 0·6). Sows in group E had lower lactational and post-weaning plasma LH levels (P < 0·001). They also had greatly attenuated preovulatory LH rises and the area under the peak was reduced (P < 0·01 and P < 0·001, respectively). Preweaning plasma prolactin levels were higher at 9 days of lactation than at 34 days and levels in both groups dropped precipitously subsequent to piglet removal. Although peak levels of prolactin at oestrus did not differ between treatments, they tended to occur before the LH peak in sows of Group C and after the LH peak in Group E. No treatment differences were detected in plasma levels of oestradiol-17β or progesterone. These results suggest that the poorer reproductive performance of sows after a very short lactation is due, at least in part, to a reduced release of LH at the first post-weaning oestrus.

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G. W. Smith, P. C. Gentry, B. Bao, D. K. Long, R. M. Roberts, and M. F. Smith

Extensive extracellular matrix remodelling occurs within the lifespan of the corpus luteum, particularly during corpus luteum formation and regression. A major mechanism for the regulation of extracellular matrix remodelling is via local production of specific proteinase inhibitors, such as the serine proteinase inhibitor plasminogen activator inhibitor type-1 (PAI-1). The objective of the present study was to characterize the localization, ontogeny and regulation of PAI-1 expression within ovine corpora lutea. Urokinase binding activity was detected within medium conditioned by ovine luteal cells. Production of PAI-1 by ovine luteal cells was confirmed by immunoprecipitating it from labelled proteins in culture medium. mRNA encoding PAI-1 was present within developing (day 3), mature (day 10) and regressing (30 h after prostaglandin F injection on day 10 after the onset of oestrus) corpora lutea as demonstrated by in situ hybridization. The ontogeny of PAI-1 mRNA expression was characterized within corpora lutea collected on days 3, 7, 10, 13 and 16 after the onset of oestrus (n = 4, 4, 4, 3 and 4, respectively). Expression of PAI-1 mRNA did not differ during the luteal phase (P= 0.06), although a trend for an increase in the amount of PAI-1 mRNA was observed on day 16. Expression of PAI-1 mRNA was also examined during luteal regression in corpora lutea collected 0, 6, 12, 24 and 36 h after injection of prostaglandin F on day 10 after the onset of oestrus (n = 4 at each time). Relative PAI-1 mRNA concentrations changed significantly during luteolysis induced by prostaglandin F (P = 0.0002). Administration of prostaglandin F resulted in a transient sevenfold increase in PAI-1 mRNA 6 h after injection (P = 0.0001) but by 12 h the amounts had returned to values similar to those detected on day 10. We conclude that PAI-1 is a major secretory product of ovine luteal cells and that a transient increase in PAI-1 mRNA occurs during luteolysis induced by prostaglandin F. PAI-1 probably plays a key local role in the control of extracellular proteolysis during the luteal phase.

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K. M. Smith, P. C. W. Lai, H. A. Robertson, R. B. Church, and F. L. Lorscheider

Summary. Maximal concentrations of AFP, measured by RIA, were obtained in fetal plasma and amniotic and allantoic fluid between the 3rd and 4th month of gestation, with levels declining thereafter until term. AFP values in maternal plasma were unchanged. Throughout gestation, AFP values were higher in allantoic than in amniotic fluid and the ratio of allantoic fluid/amniotic fluid AFP was significantly correlated with gestational age.

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L. S. Leshin, S. M. P. Raj, C. K. Smith, S. C. M. Kwok, R. R. Kraeling, and W. I. Li

Pig seminal proteins PSP-I and PSP-II are major protein components of boars' ejaculate and are present as heterodimers (PSP-dimer) in seminal plasma. These proteins were examined for their ability to modulate pig lymphocyte activity in vitro in mitogen-induced lymphocyte proliferation assays and in one-way mixed lymphocyte reactions. Pig lymphocytes were cultured with phytohaemagglutinin, concanavalin A, or pokeweed mitogen (PWM) in the presence or absence of pig seminal proteins and the amount of cellular [3H]thymidine was used as an indication of proliferation. In the absence of mitogens, none of the three pig seminal proteins affected lymphocyte proliferation suggesting that these proteins are not antigenic or mitogenic. PSP-dimer enhanced lymphocyte proliferation induced by PWM (156–227%, P < 0.05) in a concentration-dependent manner, but had no effect on phytohaemagglutinin- or concanavalin A-induced proliferation. PSP-I enhanced (127–185%, P < 0.05) phytohaemagglutinin-induced proliferation. PSP-II augmented (130–240%, P < 0.05) lymphocyte proliferation induced by concanavalin A and PWM. Lymphocytes from gilts were significantly more responsive to concanavalin A- and PWM-induced lymphocyte proliferation in the presence of PSP-I compared with boars (concanavalin A: gilts 131%, boars 91%; PWM: gilts 188%, boars 134%; P < 0.05). In the mixed lymphocyte reaction, pretreating stimulating cells with increasing concentrations of PSP-I or PSP-II elicited a 400% concentration-dependent increase (P <0.01) in lymphocyte proliferation. The abundance of pig seminal proteins in boar seminal plasma, their ability to enhance lymphocyte proliferation, and their previously reported ability to bind to lymphocytes suggest that these proteins are immunostimulatory and supports the hypothesis that they modulate uterine immune activity to ensure reproductive success.