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  • Author: BRENDA M. SCHOFIELD x
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L. PH. BENGTSSON and BRENDA M. SCHOFIELD

Summary.

In a series of thirteen sheep, experiments were carried out during the last month of pregnancy to assess the extent of progesterone influence on the myometrium. Staircase effects were recorded from the longitudinal fibres of the myometrium in the intact ewe and also in vitro, and the threshold dose of oxytocin required to elicit a contraction was determined. The results, both in vivo and in vitro, demonstrate that the progesterone influence declines before parturition and it is concluded that the extrusion of the foetus is accomplished by an oestrogendominated myometrium. This finding is discussed in relation to the fact that no fall in the progesterone level in blood can be detected before parturition. The oxytocin thresholds determined in vivo suggest that the sensitivity of the myometrium increases with the approach to parturition.

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L. Ph. BENGTSSON and BRENDA M. SCHOFIELD

Summary.

A flock of thirty ewes was observed through two pregnancies to determine whether parturition could be delayed by the systemic administration of gestagens. In the first season, the four treated groups received daily injections of 2·5 and 10 mg, 6α-methyl-17α-hydroxy-progesterone acetate (6-map) and 10 and 40 mg progesterone for 14 days starting 1 week before the expected date of delivery. The time and course of delivery appeared to be unaffected. The following season the dose levels were increased to 25 and 40 mg 6-map, and 80 and 160 mg progesterone. A high proportion of pregnancies was affected by this treatment. Some sheep delivered to schedule but most of the others had to be subjected to Caesarian section. The mortality of lambs delivered at term was higher than in the control group and in all the cases of delayed parturition the lambs died in utero. The foetal death was not considered to be due to post-maturity. The results are discussed and it is concluded tentatively that placental progesterone in the ewe is not replaceable by systemic progesterone.

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J. C. HINDSON and BRENDA M. SCHOFIELD

A series of experiments has recently been carried out in ewes at the end of pregnancy in which parturition was monitored by the recording of intra-uterine pressure changes (Hindson, Schofield, Turner & Wolff, 1965; Hindson, Schofield & Turner, 1967, 1968). Some further observations have since been made which are relevant to the conclusions drawn; this paper is by way of being a postscript to the previous publications and carries the additional information.

The frequency of the intra-uterine pressure waves associated with parturition in this series was expressed as time per six waves. Since frequency can also be

article image expressed in waves per unit time, it seemed appropriate to make a second analysis in order to substantiate the conclusion drawn. Therefore, the original tracings were analysed in