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Two methods are described for the measurement of uterine blood flow in the pregnant rabbit. The first involves the use of a Parks ultrasonic Doppler probe placed over the exposed uterine artery. The second method uses a drop counter system connected between the uterine and jugular veins. The Doppler flowmeter was used to measure uterine arterial blood flow in twenty rabbits on Day 28 or 29 of pregnancy. No significant difference was observed between blood flow on these 2 days and the absolute blood flow to one horn (±S.E.) was found to be 16·8±1·4 ml/min, equivalent to 27·1±1·8 ml/100 g tissue/min. Using the drop recorder technique, the flow to one uterine horn in eleven rabbits on Day 27 or 28 of pregnancy was 12·5±1·9 ml/min, equivalent to 23·6±3·2 ml/100 g tissue/min. The pressure-flow relationship in the uterine vascular bed was studied using the Doppler flowmeter and graded mechanical occlusion of the arterial supply. Within the range of pressures studied, the flow was found to be linearly related to the arterio-venous pressure difference. This suggests that the uterine vascular bed was fully dilated under the conditions of study.

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Experiments are described which were designed to examine the possibility that death of the goat × sheep hybrid foetus is due to the passage of haemolytic antibody from mother to foetus. 'Naturally occurring' haemolytic antibodies to sheep red cells were found in the sera of some goats with normal or hybrid pregnancies. 'Heterologous' anti-bodies, considered to be of the immune type, were found in some but not all goats with hybrid foetuses; these 'heterologous' antibodies were not found in goats carrying goat foetuses. No immune globulins of maternal or foetal origin were found in foetal plasma or in allantoic or amniotic fluids. No real evidence was obtained for the presence of immune globulins on the red cells of hybrids whether or not their mothers had anti-sheep haemolysins in their sera. It is concluded that haemolytic antibodies are not responsible for the death of the goat× sheep hybrid foetus.

The electrophoretic pattern of hybrid haemoglobin was examined.

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B. P. Setchell, M. J. D'Occhio, M. J. Hall, M. S. Laurie, M. J. Tucker, and J. L. Zupp

Summary. Normal female rats were mated to control males or males which were subjected to unilateral testicular heating (43°C for 30 min), irradiation (500 R), efferent duct ligation, arterial ligation or castration; in all males, the contralateral ductus deferens was ligated. All treatments caused reduced fertility and eventually infertility, as judged by the percentage of females becoming pregnant; the infertility was temporary after heating and irradiation. During the periods of reduced fertility, the numbers of fetuses per pregnant female and the fetus/corpus luteum ratios were reduced. In subsequent experiments, after heating of the testis, there was not only failure of fertilization despite the presence of normal numbers of spermatozoa in the uterus, but also an increased rate of embryonic degeneration in normal females.

These results provide evidence that the male, while still fertile, can affect the fecundity of the female and the rate of embryo mortality.

Keywords: embryonic mortality; subfertility induced by heat; rat

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K. Leung, V. Padmanabhan, L. J. Spicer, H. A. Tucker, R. E. Short, and E. M. Convey

Summary. Thirty primiparous suckling beef cows were slaughtered on Day 7, 14, 28,42 or 56 after parturition. Some had resumed oestrous cyclicity by the time they were slaughtered on Days 42 and 56. Amongst acyclic cows between Days 7 and 42, pituitary LH concentrations and basal and GnRH-induced release of LH from pituitary explants doubled. Pituitary FSH concentration and basal release in FSH increased only by 15–20%, while GnRH-induced release of FSH in vitro was unchanged. During post-partum anoestrus, overall mean concentrations of serum FSH did not change, whereas overall mean concentrations and pulse amplitudes of serum LH increased. Numbers and affinity constants of GnRH-binding sites in pituitary glands remained constant during the post-partum period studied. We conclude that, under these experimental conditions, numbers and affinity constants of GnRH-binding sites in the pituitary gland of post-partum beef cows do not limit the ability of the anterior pituitary gland to release gonadotrophins.