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Biomedical subjects

G Jenkin

Publications and source records attributed to G Jenkin.

At least 91 records · Page 5Linked to original sources
PubMed1980

Plasma concentrations of progesterone and 13,14-dihydro-15-keto-prostaglandin F-2 alpha at parturition in the bandicoot, Isoodon macrourus.

The concentration of progesterone in maternal plasma of the bandicoot increased from 3.9 to 12.6 ng/ml between 11 and 4 days before parturition and remained at this level for at least 7 days. Concentrations of 13,14-dihydro-15-keto-prostaglandin F-2 alpha increased from basal levels of 288 pg/ml (4 days before birth) to maximal levels of 2534 pg/ml immediately after parturition, then decreased progressively. It is suggested that PGF-2 alplha, but not progesterone, influences the initiation of parturition in this species.

Animals↗
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↗
PubMed1980

Concentrations of placental lactogen in chronically catheterized ewes and fetuses in late pregnancy.

The concentration of ovine placental lactogen (oPL) was measured by radioimmunoassay in plasma samples from chronically catheterized ewes and their fetuses from day 110 of gestation to term (about day 145). Concentrations of oPL in the plasma of the mother and fetus were raised after surgery, and remained raised for 3--5 days after the operation. Concentrations of oPL were greatest in the fetus at days 120--124 of gestation, and then declined until delivery. Mean concentrations of oPL in the fetus in late pregnancy for single, twin and triplet pregnancies were 101 +/- 6 (S.E.M.), 100 +/- 11 and 115 +/- 59 ng/ml respectively and were not significantly different. Mean concentrations of oPL in the mother in late pregnancy for single, twin and triplet pregnancies were 718 +/- 227, 1387 +/- 160 and 1510 +/- 459 ng/ml respectively; the difference between these means was significant (P less than 0.05). Peak concentrations were noted at days 130--139 of gestation after which concentrations fell and were significantly lower on the day of delivery (P less than 0.01). Concentration of oPL in the mother showed no circadian rhythm. The mean concentrations of oPL in maternal plasma during late pregnancy was significantly correlated to the combined fetal weight at birth (r = 0.624, P less than 0.01).

Animals↗
PubMed1979

The relation between plasma oestrogen, progesterone and prolactin concentrations and the efficacy of vaginal prostaglandin E2 gel in initiating labour.

In an attempt to relate the efficacy of treatment to endogenous hormone levels, plasma oestrogen, progesterone and prolactin levels were analysed in women at term following the vaginal administration of prostaglandin E2 gel to induce labour. Patients who went into labour after treatment had significantly higher oestradiol-17 beta levels before treatment compared with those requiring formal surgical induction the following day. No difference could be demonstrated in levels of progesterone or prolactin in the two groups of patients. The significance of these results is discussed.

Estradiol↗
PubMed1978

Pituitary responsiveness to LH-RH and TRH and the effects of progesterone or progesterone and oestradiol treatment in anoestrous sheep.

Pituitary responsiveness to 200 microgram synthetic LH-RH and to 10 microgram TRH was determined in anoestrous sheep before and after treatment for 3 weeks with progesterone (100 mg/day), or oestradiol (250 microgram/day) plus progesterone (100 mg/day). There was a marked decrease in pituitary responsiveness to LH-RH after progesterone (P is less than 0.01), or oestradiol plus progesterone (P is less than 0.01) treatments, and an increase in response to TRH after oestradiol plus progesterone (P is less than 0.01) treatment. The results demonstrate selective and simultaneous feedback effects of oestradiol and progesterone on pituitary responsiveness to two hypothalamic releasing hormones.

Anestrus↗
PubMed1978

Prostaglandins in the sheep fetus: implications for fetal function.

1. In chronically catheterized sheep fetuses, during normal pregnancy, the concentration of PGE in the fetal femoral arterial plasma is invariably greater than that of PGF, and increases during the 12 to 24 hr preceding delivery. The concentration of both PGE and PGF decreases repidly after birth. 2. These changes in fetal prostaglandin levels contrast with the marked increase in PGF, but negligible increase in PGE, in the maternal uteroovarian vein before parturition. 3. The changes in prostaglandin concentrations in fetal plasma at term are associated with only small changes in the concentrations of PGE and PGF in tracheal fluid. In amniotic fluid the concentrations of PGE and PGF increase during the last 4 days in utero. At birth the concentrations of PGE and PGF in fetal urine are similar to the concentrations in amniotic fluid. 4. The concentration of PGE in fetal plasma and in tracheal fluid is significantly elevated for up to 3 days after surgery. The concentration of PGF is significantly elevated in fetal plasma nad tracheal fluid for at least 24 hr after surgery. 5. Three fetuses which were chronically hypoxemic had elevated plasma PGE concentrations in utero. However, acute (1 hr) hypoxia or hypercapnia induced in the fetal lamb by making the ewe breathe appropriate gas mixtures did not produce consistent changes in fetal plasma prostaglandin concentrations. 6. During late pregnancy (day 128) exogenous PGE2 infused at about 1.6 microgram/min for 60 min into the fetal carotid artery achieved concentrations in the fetal femoral artery which were within the physiological range seen at term. At this infusion rate, there was no effect on fetal arterial Po2, Pco2, pH, or hematocrit, and no consistent effect on fetal blood pressure or heart rate. PGE2 infusion had no significant effect on the concentration of growth hormone or prolactin in fetal plasma. Within 30 min after beginning the infusion, however, there was a significant increase in the cortisol concentration in fetal plasma. This effect was seen even at times in pregnancy when the fetal adrenal gland responds only poorly to exogenous or endogenous ACTH.

Amniotic Fluid↗
PubMed1977

Progesterone and oestrogen in pregnancy and parturition: comparative aspects and hierarchical control.

The different ways in which the progesterone requirements of pregnancy are met in various species are reviewed here. Progesterone production expressed in terms of metabolic body weight lies within about one order of magnitude in several species (but not in the rat), whether the hormone is predominantly ovarian or placental in origin. Parturition is usually preceded by a decrease in the plasma concentration of progesterone and the evidence which suggests that a decrease in secretion involves enzyme induction is summarized. In the sheep a sequence of well-marked hormonal changes can be discerned--an increase in fetal cortisol secretion followed by a fall in placental progesterone and a rise in oestrogen and prostaglandin F2alpha secretion. This sequence has been interpreted in terms of hierarchical control theory which envisages a series of levels placed in a descending order of importance and in which there is a downward transmission of a signal from a higher level that modifies activity at a lower level. A dominant level in the hierarchy in the sheep and pig seems to be the fetal hypothalamus and pituitary, but in the rabbit the maternal hypothalamus, pituitary and ovary play a more dominant role.

Adrenal Glands↗
PubMed1977

Pituitary responsiveness to synthetic LH-RH and pituitary LH content at various reproductive stages in the sheep.

In sheep the basal concentration of LH in jugular vein plasma was significantly higher during the first 50 days of gestation in late pregnancy or at parturition. The pituitary response to a single i.v. injection of 200 microng synthetic LH-RH was determined at different stages of gestation and compared with that of anoestrous and cyclic sheep. Pituitary response to LH-RH decreased progressively with advancing gestation: by 56 days after mating the response had declined to 35% and by parturition to 14% of the value in anoestrous sheep. The pituitary response to LH-RH increased after parturition and the pattern of recovery differed in non-lactating and lactating sheep. By 63 days postpartum the response to LH-RH in non-lactating and lactating animals had returned to values similar to those in sheep during anoestrus and sheep during the luteal phase of the oestrous cycle. A decrease in pituitary responsiveness during pregnancy was associated with a decrease in pituitary content of LH. The quantity of LH released in response to a standard injection of LH-RH was linearly related to pituitary LH content.

Animals↗