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Biomedical subjects

R F Seamark

Publications and source records attributed to R F Seamark.

At least 127 records · Page 7Linked to original sources
PubMed1980

Ripening of the human cervix and induction of labour with purified porcine relaxin.

In a randomised double-blind trial 10 of 30 patients given 2 mg of intravaginal purified porcine relaxin on the evening before surgical induction of labour went into labour before the proposed induction. Of 30 control patients, none went into labour. Of the 30 patients treated with relaxin, 25 had improved cervical scores after treatment and significantly fewer required augmentation in labour with intravenous oxytocin than the control group. Administration of relaxin was associated with very little increase in uterine activity and no side-effects. The trial shows that exogenous relaxin causes cervical ripening and can initiate parturition. Endogenous relaxin may have a similar role.

Animals↗
PubMed1980

Specific quantitation of urinary 6-hydroxymelatonin sulphate by gas chromatography mass spectrometry.

6-Hydroxymelatonin sulphate, a unique urinary metabolite of melatonin, has been measured in human subjects for the first time using a chromatography mass spectrometry and an isotope labelled internal standard. Urinary levels in both males and females were similar and ranged from 25-125 nmol 24 h-1. A significant nocturnal elevations of 6-hydroxymelatonin sulphate was also established in a male subject.

Deuterium↗
PubMed1980

Differential production of PGF and 6-keto-PGF1 alpha by the rat endometrium and myometrium in response to oxytocin, catecholamines and calcium ionophore.

Uterine horns for castrated, estrogen-treated rats wee superfused for 6 hours in 95% O2/5% CO2 at 37 degrees C. The method of superfusion in which medium flows separately over the inner and outer surfaces of the horn allows prostaglandin synthesis in the myometrium and endometrium to be measured independently while their anatomical relationship is undisturbed. Prostaglandins were measured by radioimmunoassay. They myometrium formed more 6-keto-PGF1 alpha than PGF whereas the opposite was true of the endometrium. Production rates of TxB2 in both tissues were relatively low. The addition of inophore A-23187, oxytocin or phenylephrine to the superfusion medium not only increased the myometrial production rates of both 6-keto-PGF1 alpha and PGF but also increased the ratio of 6-keto-PGF1 alpha:PGF. Neither ionophore nor phenylephrine affected the rate of prostaglandin synthesis in the endometrium whereas oxytocin caused a significant increase in the production rate of PGF. We conclude that the large amounts of 6-keto-PGF1 alpha in the myometrial superfusate probably originate in both the smooth-muscle cells of the myometrium and the endothelium of the myometrial blood vessels. The differential responses to ionophore A-23187, phenylephrine and oxytocin suggest differences in the mode of their regulation of prostaglandin synthesis.

6-Ketoprostaglandin F1 alpha↗
PubMed1980

Circulating levels of melatonin following its oral administration or subcutaneous injection in sheep and goats.

The effect of differing doses and routes of administration of melatonin on plasma melatonin levels in sheep and goats has been examined. Melatonin injected subcutaneously in a saline or oil vehicle caused high transitory peaks in plasma melatonin whereas oral administration, in either saline solution or adsorbed onto pelleted foodstuff, resulted in sustained elevated blood levels for periods exceeding 7 h. Oral dosages of about 2 mg proved adequate to raise the normal daytime plasma levels in both sheep and goats to levels within the normal night-time range. It was concluded that with ruminants the oral route of administration provides a convenient and practical way of administering melatonin for physiological study.

Administration, Oral↗
PubMed1980

Measurement of urinary production rates of melatonin as an index of human pineal function.

The urinary production rate of melatonin has been estimated for two male subjects at approximately 30 micrograms per 24 h by measurement of the specific incorporation of deuterium label into 6-hydroxy melatonin sulphate following administration of deuterium-labelled melatonin as an isotopic tracer. No pharmacological effect due to the tracer was apparent on endogenous melatonin secretion and the production rates calculated were unaffected by either dosage or time of administration. It is, therefore, concluded that the use of deuterium-labelled melatonin coupled with quantitative gas chromatography-mass spectrometry offers a practical procedure for providing a clinically useful index of melatonin production in man.

Adult↗
PubMed1979

Summer and winter cycles in plasma melatonin levels in the elephant seal (Mirounga leonina).

Plasma melatonin concentration of immature male elephant seals was determined by radioimmunoassay. Comparison of concentrations during two 24-h periods, one in midsummer and one in midwinter, showed that there was a marked circadian cycle in winter which was greatly modified during the long day length of summer. It is suggested that in summer there was sufficient ambient lighting during the night hours to depress the nocturnal rise in plasma melatonin. The complexity of pineal cycles in the natural environment is stressed, and in this regard the polar regions are of particular interest due to the extreme seasonal changes in day length there.

Animals↗
PubMed1979

Prenatal diagnosis of placental sulphatase deficiency.

A gas chromatographic procedure for the quantitation of neutral steroid sulphates in maternal urine and its application to a suspected case of placental sulphatase deficiency is described. Low levels of oestriol coincident with elevated 16-hydroxylated metabolites of dehydroepiandrosterone in the maternal urine are shown to occur in this particular condition, and thus provide a convenient differentiation from fetal adrenal hypoplasia before birth.

Androstenediols↗
PubMed1979

Plasma melatonin, luteinizing hormone, follicle-stimulating hormone, prolactin, and corticoids in two patients with pinealoma.

Plasma melatonin, LH, FSH, PRL, and corticoids were measured in two patients with pineal tumors. Plasma melatonin was not detectable (less than 7 pg/ml) in either patient while gonadotropin and cortisol levels were within the normal range. One patient exhibited low PRL levels and the other patient, a prepubertal boy, had elevated levels. The clinical value of the measurement of melatonin as a potential marker for all pineal tumors must be questioned.

Adolescent↗
PubMed1979

Progestagen metabolites in fetal sheep plasma: the effect of fetal nephrectomy.

Fetal sheep (100-115 days gestation) were surgically implanted with femoral arterial and venous cannulae and then either sham-operated (control) or bilaterally nephrectomized. Following a 5-day recovery period, fetal blood samples (10 ml/48 h) were taken and the steroid sulphate fraction analysed as trimethylsilyl esters by gas-liquid chromatography (g. l.c.). Three progestagen metabolites were repeatedly detected in plasma samples from control and nephrectomized fetuses and identified by g.l.c.-mass-spectrometric techniques as 5 beta-pregnane-3 beta,20 beta-diol, 5 beta-pregnane-3 beta,20 alpha-diol and 5 beta-pregnane-3 alpha,20 alpha-diol. In three control fetuses the plasma concentration of both 5 beta-pregnane-3 beta,20 beta-diol and -20 alpha-diol showed a steady increase from about 0.5 micrograms/ml at 105 days to about 1.5 and 2-2.5 micrograms/ml, respectively, at 143 days gestation. A study in one fetus indicated that the values then fell precipitously by term (147 days) as plasma cortisol concentrations rose. In contrast, whilst no consistent patterns were seen in their concentration in five nephrectomized fetuses the levels were 2-10 times higher than the control values (0.5-10 micrograms/ml) at all stages. The plasma concentration of 5 beta-pregnane-3 alpha,20 alpha-diol was less perturbed by nephrectomy and only showed a slight increase over control values (0.2-0.5 micrograms/ml). Three sham-operated fetuses which aborted following infection also showed increased plasma concentrations of 5 beta-pregnane-3 beta,20 beta-diol and -20 alpha-diol, similar to the nephrectomized fetuses. It is postulated that high levels of circulating progesterone metabolites may reflect induced increases in adrenal endocrine activity culminating in premature activation of those changes in adrenal function which trigger parturition.

Animals↗
PubMed1978

Seasonal variation in steroid biosynthesis by the testis of the lizard Tiliqua Rugosa.

1. Seasonal change in the biosynthesis of androgens by testicular tissue from a scincid lizard Tiliqua rugosa has been studied in vitro using [7-3H]pregnenolone and [4-14C]progesterone as substrates. 2. Evidence is presented for the synthesis of epitestosterone, testosterone, androstenedione, 17 alpha-hydroxyprogesterone, 20 beta-hydroxypregn-4-en-3-one, and 17 alpha, 20 beta-dihydroxypregn-4-en-3-one. 3. Epitestosterone was the major conversion product. Its yield was highest (68%) during summer and lowest (14%) during spring. The yield of testosterone was maximal (10%) during spring (mating season). The production of 20 beta-hydroxypregn-4-en-3-one was highest during spring and undetectable during summer. 4. Histological evidence and changes in testicular weight indicated that spermatogenic activity was greatest during spring. Pronounced regression of the testis occurred immediately after the breeding season and lasted until autumn.

Acclimatization↗
PubMed1978

Changes in plasma tryptophan and melatonin content in penned sheep.

The present study was undertaken to examine the relationship between the plasma levels of melatonin and its precursor tryptophan. No circadian changes in plasma total tryptophan content were evident which could be related to the marked night-time rise in plasma melatonin. An automated programmable blood sampling device suited to studies of circadian rhythms in blood constituents is described.

Animals↗
PubMed1978

Prostaglandin F in the fallopian tube secretion of the ewe.

Oviducal secretions were obtained from conscious unrestrained ewes throughout the oestrous cycle via indwelling cannulae and the content of prostaglandin F (PGF) was determined by radioimmunoassay. Levels of PGF of up to 230 ng/ml were found in oviducal fluids obtained from ewes showing regular patterns of secretion and normal cyclical ovarian function as indicated by plasma progesterone measurement. Relatively large day to day fluctuations in content were evident, but there was no consistent relationship between concentration and stage of the oestrous cycle. Concentrations of PGF in excess of 100 ng/ml were common in preparations where autopsy later revealed infection or tissue irritation, and the concentration of PGF invariably exceeded 75 ng/ml when the concentration of protein in the oviducal fluid was abnormally high.

Animals↗
PubMed1978

Inhibition of cholesterol biosynthesis in ovine ovarian follicles in vitro by human chorionic gonadotrophin.

Cholesterol biosynthesis from DL-[2-14C]mevalonic acid ([14C]MVA) was demonstrated in ovine ovarian follicles and isolated thecal tissues and granulosal cells incubated in vitro. Thecal tissues more readily synthesized cholesterol than did granulosal cells when incubated separately, but in the intact follicle the newly synthesized cholesterol distributed evenly between the two tissue layers, indicating that the theca could act as a supplementary source of cholesterol for the granulosal cells. Human chorionic gonadotrophin (hCG) added to the incubation medium was found to inhibit cholesterol biosynthesis from [14C]MVA by intact follicles and isolated thecal tissues, but not granulosal cells. This hCG-induced inhibition was evident in whole follicles incubated for 12--48 h, but not at 3--6 h, and was demonstrated in thecal tissues incubated for 3 h. In all cases where inhibition of cholesterol biosynthesis was observed, 14C label accumulated in a product characterized by thin layer and vapour phase chromatography as lanosterol, implying that the hCG block lies between lanosterol and cholesterol. Treatment of follicles with hCG also reduced the amount of 14C label incorporated into the cholesteryl ester fraction. These changes were accompanied by a corresponding reduction in the tissue content of cholesteryl ester, but there were no changes in the specific activities to indicate that newly synthesized cholesteryl ester was used selectively as a substrate for progestin biosynthesis.

Animals↗