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G D Thorburn

Publications and source records attributed to G D Thorburn.

At least 91 records · Page 5Linked to original sources
PubMed1986

Characterization of particle-associated choriomammotrophin and progesterone in ovine placentomes.

The subcellular distribution and compartmentalization of choriomammotrophin (CM) and progesterone within ovine placentomes was investigated using differential and density gradient centrifugation techniques. Approximately 67% of placental CM and 45% of progesterone was associated with subcellular particles. The 10,000 g particulate fraction contained the highest specific activity of both CM and progesterone (19.1 +/- 3.8 (S.E.M.) micrograms/mg and 71.5 +/- 9.2 pmol/mg protein respectively). This fraction was also shown to contain electron-dense granules with morphology similar to that of hormone-containing secretory granules isolated from other endocrine tissues. Particle-associated CM sedimented to a density of 1.051-1.054 g/ml in colloidal silica gradients and displayed physicochemical characteristics consistent with its storage in secretory granules. During in-vitro incubations, particle-associated CM was stable for up to 90 min, but dissociated when incubated in hypoosmotic medium. Particulate progesterone, which was also present in the CM-rich fraction and was stable for up to 90 min of incubation, was not affected by decreasing the osmolality of the incubation medium. These data suggest that ovine CM (but not progesterone) is stored within a population of secretory granules located within placentomes.

Animals↗
PubMed1986

Effect of electroimmobilisation on ovine plasma concentrations of beta-endorphin/beta-lipotrophin, cortisol and prolactin.

The effect of electroimmobilisation on the plasma concentrations of beta-endorphin/beta-lipotrophin (beta-EP/beta-LPH), cortisol and prolactin (PRL) has been assessed in sheep. Serial blood samples were collected from control and electroimmobilised animals during the first and fourth of a series of four repeated treatments over two days. After electroimmobilisation the mean (+/- SEM) plasma concentrations of beta-EP/beta-LPH increased significantly from 132 +/- 19 pg ml-1 to 545 +/- 111 pg ml-1; the plasma concentrations of cortisol also increased significantly from 22.3 +/- 3.5 ng ml-1 to 108.0 +/- 12.9 ng ml-1. There was no significant change in plasma PRL concentrations after electroimmobilisation and also no significant difference between the plasma concentrations of PRL in the control and electroimmobilised animals. There was no significant difference between the effects of the first and fourth exposure to electroimmobilisation on the plasma concentrations of beta-EP/beta-LPH, cortisol and PRL. These results suggest that the endocrine response to electroimmobilisation may be specific to the pituitary-adrenal axis.

Animals↗
PubMed1986

Effect of reduced uterine blood flow on fetal and maternal cortisol.

We have measured the changes in fetal and maternal plasma concentrations of cortisol in relation to blood gases and percent oxygen saturation during 2- and 4-h episodes of reversibly reduced uterine blood flow in sheep between 120 days gestation and term. During that period of reduced uterine blood flow there was a significant decrease in fetal arterial percent oxygen saturation (SaO2), PO2 and pH. Fetal SaO2 decreased from 59.5 +/- 3.2% to 31.8% +/- 2.8% by 15 min, 32.9 +/- 2.9% by 60 min, and 33.5 +/- 2.9% by 120 min. Fetal PO2 decreased from 3.2 +/- 0.1 KPa to 2.0 +/- 0.2 KPa by 15 min, 2.2 +/- 0.2 KPa by 60 min and 2.3 +/- 0.1 KPa by 120 min. Fetal pH decreased from 7.36 +/- 0.01 to 7.30 +/- 0.03 by 15 min, 7.27 +/- 0.02 by 60 min and 7.25 +/- 0.03 by 120 min. During the period of reduced uterine blood flow, fetal plasma concentrations of cortisol increased from 37.1 +/- 10.8 nmol/l to 53.3 +/- 9.2 nmol/l by 15 min, 49.2 +/- 11.4 nmol/l by 60 min and 43.3 +/- 9.0 nmol/l by 120 min. The greatest percentage increase in fetal plasma concentrations of cortisol occurred in fetuses of 126-139 days gestation. There was no significant change in maternal blood gases, SaO2 or plasma concentrations of cortisol. These experiments demonstrate that there is a significant increase in fetal plasma concentrations of cortisol in response to reductions in uterine blood flow from as early as 120 days gestation.

Animals↗
PubMed1985

Detection of endogenous epidermal growth factor-like activity in the developing chick embryo.

Epidermal growth factor-like activity has been detected by radioreceptor assay and radioimmunoassay in the developing chick embryo. Very little activity could be detected prior to Day 8 of embryonic life (hatching is at Day 21). A peak of EGF activity was detectable by both assays over Days 10 to 12. The EGF activity then fell to virtually undetectable levels during Days 14 to 17. A later rise in RRA detectable EGF like activity was then observed over Days 18-20. The EGF activity from a Day 11 embryo chromatographed on high-performance liquid chromatography as a single peak, with very high recovery of activity, at a later elution position than mouse EGF or human EGF.

Animals↗
PubMed1985

Inhibition of progesterone secretion by a 3 beta-hydroxysteroid dehydrogenase inhibitor in late pregnant sheep.

The role of progesterone in the initiation of parturition in the sheep is unclear. Whether a decrease in plasma progesterone is the essential prerequisite for the initiation of parturition or whether other factors also maintain uterine quiescence until delivery is not known. The effect of withdrawal of progesterone on the initiation of parturition has been investigated by intravenous administration of trilostane, a 3 beta-hydroxysteroid dehydrogenase delta 5-4 isomerase inhibitor, to late pregnant sheep. Twenty-five or 100 mg trilostane caused a precipitous decrease in plasma progesterone to about 30% of preinjection levels. Progesterone remained depressed for up to 7 days after treatment. 13,14-Dihydro-15-keto-prostaglandin F2 alpha (PGFM) became elevated between 7 and 36 h after trilostane injection but gradually returned to preinjection levels during the subsequent 36 h, at a time when plasma progesterone was still depressed. Four of 11 animals treated with 100 or 200 mg trilostane aborted prematurely at a time when plasma PGFM was maximal and plasma progesterone minimal. There were no consistent changes in plasma estradiol-17 beta or ovine placental lactogen concentrations after treatment with trilostane. It is suggested that a decrease in plasma progesterone will cause a transient increase in plasma PGFM concentrations which can lead to the premature initiation of parturition. In some instances the myometrium does not appear to respond to the elevated PGFM concentrations even when the estrogen:progesterone ratio is elevated by a decrease in plasma progesterone.

3-Hydroxysteroid Dehydrogenases↗
PubMed1985

Subcellular localization of oxytocin in the ovine corpus luteum.

The subcellular localization of oxytocin within the corpus luteum of sheep was investigated using differential and density gradient centrifugation. Oxytocin was associated with a particulate fraction which sedimented to a density of 1.054-1.061 g/mL. The exclusion of [3H]oxytocin from this particulate fraction is indicative that particulate oxytocin represents endogenous compartmentalization. Particulate oxytocin, incubated in buffered medium at 37 degrees C, was stable for up to 1 h and the release of oxytocin was not affected by the pH of the incubation medium, over the range 5.5-8.5. Oxytocin release, however, was stimulated by incubating particle-bound oxytocin in buffered medium of low osmolality (less than 200 mosmol). These data are similar to the physicochemical properties reported for peptide-containing neurohypophysial secretory granules. Ultrastructural analysis of oxytocin-containing fractions revealed the presence of electron-dense granules (diameter, 200-250 nm). These data are suggestive that oxytocin, in the corpus luteum of sheep, is contained within a population of secretory granules which occur in high numbers during the midluteal phase of the oestrous cycle.

Animals↗
PubMed1985

Induction of premature delivery in sheep following infusion of cortisol to the fetus. I. The effect of maternal administration of progestagens.

Premature induction of delivery in fetuses infused with graded doses of cortisol was brought about in 123.5 +/- 7.7 h (mean +/- SEM, n = 6) after the start of cortisol infusion. This treatment caused a rise in fetal plasma cortisol similar to that observed at normal delivery. Maternal and fetal progesterone and 20 alpha-dihydroprogesterone concentrations decreased to basal levels during infusion of cortisol to the fetus. Induction of premature delivery was delayed or prevented by concomitant treatment of the ewe with progestagen. Maternal intramuscular injection of 100 mg progesterone, 2 times daily, prevented delivery in four of four ewes treated during the time that cortisol was infused into the fetus (11-13 days). Maternal plasma progesterone and 20 alpha-dihydroprogesterone concentrations were maintained during this period, but fetal plasma progesterone concentrations decreased to the same extent as in the fetuses infused with cortisol alone. A single intramuscular injection of 250 mg of medroxyprogesterone acetate to ewes on the day before commencement of infusion of cortisol to the fetus prevented delivery in four of six ewes during the time that cortisol was infused for 9, 13, 14, and 15 days, respectively. One ewe delivered a live lamb at 133.5 h and another at 147.7 h after the start of infusion of cortisol to the fetus. Maternal and fetal plasma cortisol, progesterone, and 20 alpha-dihydroprogesterone concentrations were similar to those observed during infusion of cortisol alone to the fetus. Although fetal cortisol concentrations rose in a similar fashion, and to a similar extent, in all three groups during infusion of cortisol to the fetus, fetal 11-desoxycortisol concentrations only rose above basal levels close to the time of delivery in cortisol-infused fetuses or, in the progestagen-treated groups, when the fetus showed signs of being stressed.

20-alpha-Dihydroprogesterone↗
PubMed1985

Insulin-like growth factor receptor in fetal lamb liver: characterization and developmental changes.

Multiplication-stimulating activity (MSA), an insulin-like growth factor (IGF) (rat IGF II), binds to extracts of many tissues from fetal lambs. We now report the presence of high concentrations of a glycoprotein receptor with a high affinity for MSA-II in microsomes prepared from fetal lamb liver. The binding of radiolabeled MSA-II is inhibited by IGF but not by insulin, human, and ovine GH, ovine PRL, ovine placental lactogen, and mouse epidermal growth factor. The relative potencies of human IGF II, human IGF I, and MSA-II in competing with [125I]MSA-II for binding to this receptor are 100:17:3.5 by weight. Binding is pH, time, and temperature dependent. Gel permeation chromatography of the Triton X-100 soluble receptor indicates a hydrodynamic radius of 6.8 nm. Specific binding increases from mid- to late gestation and is associated with changes in both the affinity and concentration of receptors. Receptor concentration increases from 7.95 +/- 3.94 pmol/mg (mean +/- SE) at 78 days gestation to 15.8 +/- 4.3 pmol/mg at 134-140 days (P less than 0.05), whereas receptor affinity decreases from 1.14 +/- 0.34 X 10(9) liter/mol to 0.63 +/- 0.14 X 10(9) liter/mol over this period (P less than 0.05). The presence of very high concentrations of an IGF receptor in fetal lamb liver suggest that this organ may be a major target for IGF action in fetal life. The increase with advancing gestational age of the concentration of IGF receptors which have preferential specificity for IGF II may function to increase the responsiveness of the fetal lamb liver to IGF II stimulation and so compensate for the decline in plasma concentrations of this growth factor which occur near birth.

Animals↗
PubMed1984

The influence of acute hypoxia and sleep states on the electrical activity of the cerebellum in the sheep fetus.

The experiments were designed to examine (1) the effects of acute hypoxia and (2) the influence of sleep states on the electrical activity of the cerebellum in the fetus. Five fetal sheep were instrumented between 106 and 133 days of gestation and survived in utero until term (140-146 days). Insulated stainless steel electrodes (75 microns diam.) were introduced into the cerebellar cortex and cemented in place. Electrodes were also implanted into 4 fetuses to monitor the electrocorticogram, rapid eye movements and the EMG of the dorsal neck (nuchal) muscles. Recordings of cerebellar activity were made for 252 h in 4 fetuses. The recordings were derived from many units (probably Purkinje cells) with a high level of basal discharge. The mean firing frequency was related to fetal sleep state. The highest frequencies coincided with episodes of rapid eye movements with low-voltage electrocortical activity and the lowest occurred during high-voltage electrocortical activity when rapid eye movements are absent. Acute hypoxaemia (fetal pa O2 6-10 mm Hg for up to 30 min) abolished rapid eye movements and caused a marked reduction in cerebellar activity. High-voltage electrocortical activity and nuchal EMG activity were maintained indicating that the effects of hypoxia on the cerebellum were not due simply to a general CNS depression. Cerebellar neural activity returned to normal at the termination of the hypoxic stimuli demonstrating that fetal Purkinje cells can withstand short episodes of severe hypoxia.

Animals↗
PubMed1984

Pregnancy-related changes in the connective tissue of the ovine cervix.

During the course of gestation, changes in the metabolism and chemical composition of the cervical connective tissue occur. The concentrations of collagen, proteoglycan and hyaluronate in the cervix decrease with time of pregnancy, while there is a small but significant increase in tissue hydration. The collagen network loses its dense, ordered appearance and assumes a loose, frayed, disoriented structure. A small molecular weight dermatan sulphate proteoglycan with Kav = 0.48 on Sepharose CL-4B has been isolated from pregnant and nonpregnant ovine cervix. Proteoglycans isolated from dilated cervix yield a second peak at the excluded volume of a Sepharose CL-4B column which may represent a new proteoglycan species, or represent a proteoglycan monomer with larger glycosaminoglycan constituents. The rate of synthesis of proteoglycan is enhanced during pregnancy, and doubles in the time between 140 days and term (dilated). The increased rate of proteoglycan synthesis in the presence of a diminishing hexuronate concentration in the pregnant cervix is indicative of enhanced proteoglycan turnover. This may provide some insight into the mechanism whereby a new matrix with altered mechanical properties is produced, since a rapid turnover of matrix components enables a remodeling of the connective tissue framework. This reorganization of the matrix is discussed with respect to parturition.

Animals↗
PubMed1984

Inhibition of prostaglandin synthesis by ovine allantoic fluid: acute reduction in inhibitory activity during late gestation.

The capacity of ovine allantoic fluid to modulate prostaglandin (PG) synthesis was measured in fluid taken from ewes at 100-140 days gestation. An inhibitor of PG synthesis was found in allantoic fluid from ewes at 100-130 days gestation. The inhibitor had the capacity to inhibit PGF2 alpha, PGE2, and 6-keto-PGF1 alpha synthesis by endometrial cotyledon microsomes in a concentration-dependent manner. At 140 days gestation, the inhibitory potency of the fluid was significantly less than that present at 100-130 days gestation, at concentrations greater than 20% (v/v) (p less than 0.001). The inhibitor is not albumin and remained active after boiling, dialysis, and protease treatment. It was extracted with chloroform-methanol, indicating that the active portion of the molecule is a lipid. We suggest that parturition in the sheep may be associated with a local withdrawal of inhibition of prostaglandin synthesis.

Allantois↗
PubMed1984

Identification of epidermal growth factor-like activity in human male reproductive tissues and fluids.

Epidermal growth factor-like activity (EGF-LA) has been detected in human seminal plasma in concentrations of 5-150 ngeq/ml (36.4 +/- 2.1, mean +/- SEM), using a heterologous RRA with murine EGF. The samples were obtained from normal, subfertile and azoospermic men, aged 21-50 yr. No correlation was found between EGF concentration and age of donor, sperm count, sperm motility, or period of sexual abstinence before sample collection. High performance liquid chromatography of the seminal plasma resulted in a main peak of EGF-LA which eluted at 29% acetonitrile, compared to 33% for murine EGF. Microsomal membranes were prepared from several tissues from the human male reproductive tract and were tested for their ability to bind radioiodinated murine EGF. Specific EGF binding activity was detectable in testicular membrane preparations but was not detectable in membranes prepared from human prostate, seminal vesicle, epididymis, or spermatozoa. Endogenous EGF-LA was detectable in human testis, seminal vesicle, prostate, and epididymis.

Aged↗
PubMed1984

ACTH control of steroid secretion from adrenal cells of the developing rhesus monkey (Macaca mulatta).

Cells from adrenal glands of 140-160 days foetal, neonatal and infant Rhesus monkeys (Macaca mulatta) were prepared, by collagenase digestion and incubated with 10 pg-16 ng/ml ACTH. The production of cortisol, androstenedione, corticosterone, progesterone and prostaglandins was measured. The cortisol production in the 140 day and 160 day foetuses and in the neonatal adrenal cells was comparable. It was 2-fold higher in adrenal cells of 6 month infant monkeys. In all the groups there was an increasing production of cortisol with increasing ACTH concentration, and a response to low physiological concentrations of ACTH. The androstenedione production was significantly greater in the 160 day foetuses than in either those of 140 days or of the neonate which demonstrated a poor response to increasing ACTH concentrations. It responded well to increasing ACTH in adrenal cells from 6 month infant monkeys. Corticosterone output was 1/10th of cortisol with only the 140 day foetuses showing an increase in production with increasing ACTH concentrations. The results demonstrate that cells of the primate foetal adrenal gland are not inherently unresponsive to ACTH stimulation as regards cortisol production, which per/micrograms DNA does not appear to change over the last 25 days before term.

Adrenal Cortex Hormones↗
PubMed1984

Induction of transient functional luteolysis in cyclic sheep by a 3 beta-hydroxysteroid dehydrogenase inhibitor.

The mechanism by which prostaglandin F2 alpha terminates luteal function in the sheep is unclear even though it is used extensively in animal husbandry. At the time of luteal regression, a decrease in 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity is apparent in the corpus luteum, but it is not known whether the decrease in enzyme activity is the primary cause of structural luteolysis. The effect of trilostane, a 3 beta-HSD inhibitor, on luteal function and morphology has therefore been investigated. Intravenous injection of trilostane in the mid-luteal phase of the oestrous cycle caused a decrease in ovarian tissue progesterone content. A transient decrease in peripheral and utero-ovarian vein plasma progesterone was observed but there was no significant effect on the length of the luteal phase of the cycle. There was no significant change in plasma 13,14-dihydro-15-oxo-prostaglandin F2 alpha during the period when plasma progesterone was depressed. Morphological examination of the corpora lutea revealed a decrease in the concentration of electron-dense granules without any other features of impending luteal regression. When plasma progesterone was reduced for more than 10 h by two injections of trilostane 4h apart, there was again no subsequent effect on the length of the oestrous cycle or on the return to oestrus. Plasma progesterone returned to preinjection levels within 24 h of injection. This evidence suggests that competitive inhibition of 3 beta-HSD activity, per se, is ineffective in bringing about structural luteolysis.

3-Hydroxysteroid Dehydrogenases↗
PubMed1984

Extraction and purification of murine epidermal growth factor.

We have compared six different solutions commonly used for the extraction of peptides to optimize the extraction of Epidermal Growth Factor (EGF) from mouse submandibular glands. The yield of EGF was always higher in neutral pH extractions than in acidic ones. However, the EGF extracted at neutral pH was only poorly adsorbed on to octadecylsilyl silica, whereas the EGF extracted at acidic pH was be easily adsorbed. Subsequent purification of the EGF extracts by two-stage reversed-phase High Performance Liquid Chromatography yielded highly purified EGF. Identical chromatograms were obtained from each of the different extracts. Preparative scale quantities of EGF could be purified rapidly and reproducibly at high efficiency from acidic extracts.

Animals↗
PubMed1984

Isolation of choriomammotropin from the ovine placentome.

Placentomes, taken from ewes at 101-141 days gestation, were homogenized and subjected to differential and density gradient centrifugation. In the presence or absence of protease inhibitors, choriomammotropin (ovine chorionic somatomammotropin, oCS) was detected by radio-immunoassay, and banded at two positions in 30-60% w/v sucrose gradients. The first band (soluble form) eluted in the sample zone of the gradient and contained 33 +/- 6.1% (mean +/- s.e.m., n = 10) of the total oCS present in the gradient. The remainder (48 +/- 7.6%) of the oCS (particulate form) sedimented to 37.5-43% w/v sucrose. Both these bands became sharper with decreasing protein loaded onto the gradients. 125I-oCS, pre-equilibrated with a placentome preparation, eluted in the same position as the first band of endogenous oCS. When loaded onto a second gradient the second band eluted at 38-41% w/v sucrose, but after being subjected to ultrasonic disruption or treatment with Triton X-100 this oCS eluted in the sample zone. There was no correlation between gestational age of the ewe and the percentage oCS in either the soluble or particulate form, the concentration of oCS, or enrichment by protein. We have shown that following homogenization, differential and density gradient centrifugation, oCS exists in two forms. We suggest that the particulate form of the hormone is contained within the electron-dense granules of placentome cells. The soluble form may represent oCS in the process of secretion and hormone which has leached out of the granules during homogenization and centrifugation of the placentomes.

Animals↗
PubMed1983

Ultrastructural evidence of variation in the number of secretory granules within the granulosa cells of the sheep corpus luteum.

The granulosa luteal cells of the sheep corpus luteum secrete their hormonal products by exocytosis of granules. Electron micrographs of randomly selected granulosa cells from nine corpora lutea at day 10 of the oestrous cycle were examined to obtain the cellular density of these granules. From the area of the cell, calculated using an x-y digitiser, and the number of granules observed, the number of intracellular secretory granules per microns 3 of luteal cell cytoplasm was calculated. There was a large variation in the number of granules per cell within the same corpus luteum and between corpora lutea taken at the same stage of the cycle. The number of intracellular granules in nine corpora lutea varied from 2.12 +/- 1.05 granules per microns 3 (mean, SD, n = 30) cells to 0.36 +/- 0.18 granules per microns 3 (mean, SD, n = 26). These morphological data suggest that the variation in granule synthesis in individual cells may contribute to the variation in hormone content of corpora lutea at the same stage of the cycle, and the episodic release of hormone into the plasma.

Animals↗