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N. W. BRUCE

Summary.

Temporary ischaemia of one uterine horn of anaesthetized, 9-day pregnant rats was induced by occluding the uterine blood vessels with forceps. The effects on the embryo of 30, 60 or 120 min of ischaemia was examined with the maternal abdominal temperature maintained at 32, 35 or 37° C.

Ischaemia caused a reduction in fetal survival at all treatment levels. Higher abdominal temperatures caused a greater reduction in fetal survival, as did longer periods of ischaemia. The incidence of fetal malformation was greater in ischaemic than in control horns although specific treatment effects were not apparent. Fetal weights were reduced in the ischaemic horns, especially at the higher abdominal temperatures.

These findings show that abdominal temperature can influence the effects of ischaemia and suggest that the embryo is less resistant to uterine ischaemia than was previously thought.

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N. W. BRUCE

Summary.

The left uterine artery was ligated in 1-, 2- and 7-day pregnant rats to determine the effects on conceptuses at Day 22. Uterine arterial ligation at these stages of gestation had no apparent effect on the percentage of rats holding to service, on fetal survival, the incidence of fetal malformation, fetal sex ratios or fetal weights.

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N. W. Bruce

Summary.

The rate of ovarian and utero-placental blood flow through vessels of less than 25 μm diameter was examined with radioactive microspheres in 5 non-pregnant rats and 19 rats at Day 22 of pregnancy. Total blood flow to the reproductive organs was 0·559 ml/min in the non-pregnant animals and 13·2 ml/min in those near term, a 23-fold difference. The mean ovarian blood flow was high and increased from 0·202 ml/min to 0·845 ml/min. Myometrial and endometrial blood flow increased from 0·156 to 2·24 ml/min. The mean maternal placental blood flow at Day 22 of pregnancy was 0·76 ml/min or 121 ml.min-1.100 g-1. Litter size was negatively correlated with mean fetal weight but showed little relationship to mean placental weight or to mean maternal placental blood flow.

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A. Rahima and N. W. Bruce

Summary. Longitudinal growth of the uterine horn and distances between implantation sites and the extremities of the horn were measured in 30 albino Wistar rats at Days 7, 10, 13, 16 or 22 of gestation. Growth of the uterus was most rapid over Days 13–16 but continued over Days 16–22. Distances between implantation sites and between the extremities of the uterine horn and neighbouring implantation sites were relatively even in that the coefficients of variation of these distances were 28, 32, 19, 35 and 35% at Days 7, 10, 13, 16 and 22, respectively. This indicates that an active mechanism promotes even spacing since the expected coefficients of variation given completely random spacing of conceptuses was calculated to be about 100%. Local crowding of fetuses in the uterine horn did not appear to affect fetal or placental growth except at Day 22 when there was a weak but significant correlation (r = 0·3) between fetal weight and the harmonic mean distance to neighbouring implantations.

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Kerry Herbert and N. W. Bruce

Summary. Rats (30) were injected intravenously with Evans blue dye on Day 5 of gestation and their uteri were examined to determine the position of early implantations. On Day 7 they were examined again for late implantations. Fetal sex and fetal and placental weights were determined at Day 22 (15 rats). The distribution of the 20% early implantations appeared random with respect to position in the uterine horn. There was no difference in fetal weight, placental weight or sex ratio between early and late implanting embryos.

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N. W. BRUCE and R. W. ABDUL-KARIM

Summary.

Fetal weights, placental weights, myometrial, vaginal and maternal placental blood flows (estimated with radioactive micro-spheres) were measured in forty-one rabbits at 16, 20, 24 or 28 days of gestation; term occurs around Day 31. Multiple linear regression analysis indicated that fetal weight and placental weight were positively related at all stages of gestation examined. Fetal weight and placental blood flow were negatively related at Day 16, but positively related at Days 20, 24 and 28. The conceptus adjacent to the ovary had greater placental weight and flow values than the means from all conceptuses in the horn by Day 20 but fetal weight was only greater by Day 28. The relevance of these findings to the determination of fetal weight is discussed.

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R. W. ABDUL-KARIM and N. W. BRUCE

Summary.

The effect of oestrogen on uterine and placental blood flow was studied in ovariectomized, progesterone-supplemented pregnant rabbits on Days 16 and 18 of gestation. The intravenous administration of 150 μg/kg conjugated equine oestrogens (Premarin) caused an increase in both myometrial and vaginal blood flows but a large decrease in the maternal placental flow. There was little change in total uterine blood flow and no change in intrauterine pressure.

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N. W. Bruce and G. T. Meyer

Summary. A venous outflow technique was used to estimate the rate of progesterone secretion from the ovary of rats on Day 16 of gestation. In 9 normal rats the rate of progesterone secretion was 13·7 μg/h per ovary and ovarian blood flow was 0·48 ml/min. In 6 rats in which haemorrhage had occurred the respective values were 38·3 μg/h per ovary and 0·53 ml/min. Comparison with earlier reports suggests that ovarian blood flow can be substantially reduced for short periods without affecting progesterone secretion.

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H. M. Massa and N. W. Bruce

The effects of noradrenaline on the rates of secretion of ovarian progesterone and 20α-hydroxypregn-4-en-3-one (20α-OHP), blood flow and oxygen consumption were examined in rats on day 16 of pregnancy. A modified venous outflow technique was used to infuse noradrenaline directly into the ovary, without recirculation, and to monitor subsequent changes in the ovary. Noradrenaline was infused for periods of 10 min at a low and a high concentration, which achieved effective blood concentrations of about 6.25 and 25 ng ml−1, respectively. Each period of noradrenaline infusion was interspersed by a 10 min period of infusion of its ascorbic acid carrier. Two series of infusions of low and high concentrations of noradrenaline were carried out on each rat. Neither the infusion of the ascorbic acid carrier nor of the low concentration of noradrenaline had any effect on ovarian progestin secretion. The high concentration of noradrenaline reduced blood flow by 30% but had no apparent effect on progestin secretion or oxygen consumption. Collectively, these findings question the generally accepted view that noradrenaline has a physiological role in the regulation of progesterone secretion. Further, putative luteotrophins need to be examined in the intact ovary as well as under in vitro and indirect in vivo conditions to determine their physiological role.

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N. W. Bruce and R. M. Moor

Summary.

The radioactive microsphere technique was used to determine the rate of blood flow through vessels of up to 15 αm diameter in the ovaries of 23 anaesthetized sheep in the 72 hr preceding ovulation. The validity of the microsphere technique was established in two preliminary studies.

On Days 14,15 and 16 of the cycle the rate of blood flow (ml.min-1.100 g-1 tissue) was 1122, 708 and 116 to the CL; 157, 258 and 140 to the stroma; and 637, 742 and 1096 to the follicles, respectively. Blood flow to grossly atretic follicles did not differ significantly from that to non-atretic follicles of an equivalent size. Change in blood flow do not appear to initiate or control the activation, steroidogenic function or atresia of follicles.