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Penelope A. Steele, A. P. F. Flint and A. C. Turnbull

Nuffield Department of Obstetrics and Gynaecology, John Radcliffe Hospital, Headington, Oxford, OX3 9DU, U.K.

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M. D. Mitchell, A. P. F. Flint and A. C. Turnbull

In sheep, prostaglandin (PG) F-2α concentrations rise in uterine venous plasma and in myometrium and maternal cotyledons before dexamethasone-induced parturition (Liggins & Grieves, 1971). As in many other species these high PGF-2α concentrations are thought to play a role in stimulating uterine contractions (Thorburn, Nicol, Bassett, Shutt & Cox, 1972). The experimental evidence to date does not support an acute effect of PGF-2α in the pregnant ewe (Liggins, Grieves, Kendall & Knox, 1972; Oakes, Mofid, Brinkman & Assali, 1973; Keirse et al., 1973). However, a positive effect of chronic PGF-2α administration on uterine contractility has been reported (Liggins, Fairclough, Grieves, Kendall & Knox, 1973); in this case the myometrial sensitivity to oxytocin was greatly increased after PGF infusion for 12 hr and spontaneous uterine contractions were observed after 24 hr of treatment. This report describes experiments designed to determine whether PGF-2α can exert an acute effect on uterine activity during parturition in sheep.

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M. D. Mitchell, A. P. F. Flint and A. C. Turnbull

Summary. Intrauterine pressure changes were monitored in 5 pregnant ewes and uterine venous prostaglandin (PG) F concentrations were determined after distension of the vagina. Uterine contractility and utero-ovarian PGF concentrations were elevated by vaginal distension and the magnitude of both effects increased as parturition approached.

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A. B. M. ANDERSON, C. G. PIERREPOINT, T. JONES, K. GRIFFITHS and A. C. TURNBULL

Summary.

The metabolism, in vitro, of isotopically-labelled pregnenolone and progesterone by foetal and adult sheep adrenals has been investigated. Both substrates were almost completely metabolized by the adult tissue, whereas, in the case of the foetus, only pregnenolone showed extensive metabolism. The adult adrenal converted pregnenolone mainly to cortisol, corticosterone and 11-deoxycortisol, whereas corticosterone was the major product from progesterone. The foetal adrenal, on the other hand, yielded mainly progesterone from pregnenolone with only a small conversion to the corticosteroids. The substrate, progesterone, was transformed, in the main, to 11-deoxycorticosterone. No 3β-hydroxysteroid sulphokinase-transferase activity was demonstrated in either tissue. The importance of these findings and the probable pathways involved in the formation of the biosynthetic products are discussed.

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M. J. N. C. Keirse, B. R. Hicks and A. C. Turnbull

Nuffield Department of Obstetrics and Gynaecology, University of Oxford, John Radcliffe Hospital, Oxford, OX3 9DU, U.K.

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A. P. F. FLINT, MARY L. FORSLING, M. D. MITCHELL and A. C. TURNBULL

Summary.

To investigate the rôle of oxytocin in the increase in utero-ovarian venous prostaglandin F (PGF) level caused by vaginal distension, jugular venous oxytocin and utero-ovarian venous PGF were measured simultaneously in one sheep in late pregnancy and in one sheep shortly before parturition. Vaginal distension raised oxytocin and PGF levels in both animals and oxytocin levels increased before those of PGF. These findings support the suggestion that the elevated PGF levels resulting from vaginal distension are caused by the reflex secretion of oxytocin.