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Biomedical subjects

M D Mitchell

Publications and source records attributed to M D Mitchell.

At least 307 records · Page 17Linked to original sources
PubMed1980

Prostaglandins in the human fetal circulation in mid-trimester and term pregnancy.

Concentrations of prostaglandins in fetal and maternal plasma during mid-pregnancy and fetal plasma at term have been measured. Fetal levels at both gestations were higher than found in maternal blood. The stable chemical breakdown product of prostacyclin, 6-keto-prostaglandin F1 alpha, was consistently considerably higher in the fetus during mid-pregnancy compared with at term. Prostaglandin F levels were also significantly higher in mid-pregnancy, though there was no difference in the concentrations of the major circulating prostaglandin F metabolite, PGFM. Concentrations of prostaglandin E were similar at the two stages of pregnancy. The physiological significance of these findings is discussed.

6-Ketoprostaglandin F1 alpha↗
PubMed1980

Release of prostaglandins after amniotomy is not mediated by oxytocin.

The rise in peripheral plasma levels of 13,14-dihydro-15-keto-prostaglandin F (PGFM) following amniotomy has now been shown to be maximal within five minutes of the procedure, and levels remain elevated for at least 30 minutes. There was no change in plasma oxytocin levels with amniotomy and therefore a local mechanism for prostaglandin release has been postulated.

Female↗
PubMed1980

The in vitro production of prostanoids by the human cervix during pregnancy: preliminary observations.

The ability of the pregnant human cervix to produce prostanoids has been studied using an in vitro superfusion technique. Tissues obtained from four patients during the first trimester of pregnancy produced prostaglandin E (PGE), prostaglandin F (PGF), 13,14-dihydro-15-oxo-prostaglandin F (PGFM) and 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha). Production of thromboxane B2 (TXB2) was minimal. Preliminary studies using tissue taken at Caesarean hysterectomy during the last trimester of pregnancy indicate that the cervix may show increased prostanoid production during active dilatation. The implications of these observations for an involvement of prostanoids in cervical softening during human parturition are discussed.

Cervix Uteri↗
PubMed1980

Prostaglandins in human milk.

Prostaglandins E and F have been shown to be present in breast milk in over 100 times the concentrations found in adult plasma. The ratio of the concentration of the principal circulating metabolite of prostaglandin F (13, 14-dihydro-15-ketoprostaglandin F) to prostaglandin F itself is low (0.3 to 0.5, compared with 15.8 in adult plasma), implying that prostaglandins may have a relatively long half-life in milk. In addition inactive metabolites of thromboxane A2 and prostacyclin are also found in significant amounts. It is speculated that milk prostaglandin play a role in modulating neonatal physiology--for example, gut motility.

Female↗
PubMed1980

Prostaglandins in the umbilical and uterine circulations during late pregnancy in the ewe.

Prostaglandins (PG) E and F, and 13,14-dihydro-15-keto-prostaglandin F (PGFM) were measured in plasma collected from the umbilical artery and vein, the maternal carotid artery, and the utero-ovarian vein of pregnant sheep between 116 and 139 days of gestation. PGE levels were greater than PGF levels in the umbilical artery and vein and the maternal carotid artery, but not in the utero-ovarian vein. PGFM exceeded PGF in samples from all vessels. There was a significant vein-to-artery concentration difference for PGF and PGFM, but not for PGE, in the umbilical circulation. Utero-ovarian concentrations of all 3 PGs generally exceeded their concentrations in the maternal caroitd artery.

Animals↗
PubMed1980

Delayed luteal regression in ewes immunized against oxytocin.

Active immunization of sheep against oxytocin prolonged the luteal phase of the oestrous cycle, as judged by oestrous behaviour and circulating progesterone concentrations. Mean cycle length was extended by 3.7 days. The treatment resulted in a 10-fold increase in circulating oxytocin concentrations. Antisera produced were specific for oxytocin; cross-reactions with vasotocin, arginine vasopressin, and hypothalamic releasing factors were low. Cerebrospinal fluid contained low levels of antibodies directed against oxytocin. This finding supports the hypothesis that the luteolytic action of oestradiol-17 beta in sheep may be mediated through a stimulatory effect on the endometrial oxytocin receptor concentration.

Animals↗
PubMed1980

Concentrations of oxytocin in the plasma and amniotic fluid of rhesus monkeys (Macaca mulatta) during the latter half of pregnancy.

A specific radioimmunoassay for oxytocin has been established with a sensitivity of 0.8 pg/tube. This assay has been applied to the measurement of oxytocin in serial samples of peripheral plasma and amniotic fluid from pregnant rhesus monkeys, collected at weekly intervals by venepuncture and amniocentesis. Concentrations of oxytocin in both fluids were generally low and showed no trends throughout the latter half of gestation.

Amniotic Fluid↗
PubMed1980

Concentrations of melatonin in the plasma of the rhesus monkey (Macaca mulatta).

A radioimmunoassay for the determination of concentrations of melatonin in the plasma of rhesus monkeys has been developed. Antiserum for the assay was raised against N-acetyl serotonin and there was a 100% cross-reaction with melatonin. Cross-reactivity with closely related indoles, precursors and metabolites was less than or equal to 1%. The lower of sensitivity of the assay was 4 pg/tube. The assay has been used for the investigation of diurnal variations and cyclical changes in melatonin concentrations in peripheral plasma of the rhesus monkey. The concentrations of melatonin ranged between 26.6 and 85.3 pg/ml during sampling for 24 hr. There was a distinct diurnal variation in the concentration of melatonin in plasma. The concentration during darkness (61.0+/-7.1 (S.E.M.) pg/ml) was greater (P less than 0.01) than that during illumination (40.1+/-6.1 pg/ml). There were no significant differences in the concentration of melatonin in plasma at any time during the 28 day menstrual cycle of the rhesus monkey.

Animals↗
PubMed1979

The concentrations of the prostaglandins E and F, 13 14-dihydro-15-oxo-prostaglandin F and thromboxane B2. In tissues obtained from women with and without pre-eclampsia.

The concentrations of prostaglandins E (PGE) and F (PGF), 13, 14-dihydro-15-oxo-prostaglandin F (PGFM) and thromboxane B2 (TXB2) were measured by specific radioimmunoassays in tissues obtained from women with and without pre-eclampsia. The concentrations of PGE in the amnion, chorion, decidua and placenta obtained from subjects with pre-eclampsia were significantly lower than those from subjects without pre-eclampsia. The concentration of PGE in these tissues increased significantly with gestational age and correlated with urinary oestrogen excretion. PGF concentrations were lower in the amnion and placenta of the pre-eclamptics compared to those without pre-eclampsia. The concentrations of PGFM in the amnion, decidua, and myometrium were lower in the pre-eclamptics. No significant difference in the TXB2 concentrations between the two groups of subjects were found. It is suggested that the altered tissue concentrations of prostaglandins in pre-eclamptics are due to the effects of gestational age and oestrogens and may or may not be involved in the pathogenesis of pre-eclampsia.

Adolescent↗
PubMed1979

Concentrations of the prostacyclin metabolite, 6-keto-prostaglandin F1 alpha, in amniotic fluid during late pregnancy and labour.

Concentrations of 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha, the stable metabolite of prostacyclin, PGI2) have been measured in amniotic fluid obtained during late pregnancy and labour. Samples taken at amniotomy during spontaneous labour contained a significantly greater concentration of 6-keto-PGF1 alpha than samples taken at amniotomy before the onset of labour (p less than 0.01). There was no correlation between the level of 6 keto-PGF1 alpha in amniotic fluid before labour and gestational age (p greater than 0.1). It is suggested that prostacyclin may have a functional role in the mechanism of parturition in man.

Amniotic Fluid↗
PubMed1979

The effect of cervical encerclage on plasma prostaglandin concentrations during early human pregnancy.

In women having either cervical encerclage under general anaesthesia or a vaginal examination in the early second trimester of pregnancy, peripheral plasma levels of 13,14-dihydro-15-keto prostaglandin F (PGFM) were measured before and after each procedure. A significant rise in circulating levels of PGFM was found within minutes of completing cervical encerclage but not after vaginal examination or induction of general anaesthesia.

Anesthesia, General↗