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Biomedical subjects

M D Mitchell

Publications and source records attributed to M D Mitchell.

At least 217 records · Page 12Linked to original sources
PubMed1986

The effect of fetal urine on arachidonic acid metabolism in human amnion cells in monolayer culture.

Human amnion cells in primary monolayer culture were used as a model system to evaluate the regulation of arachidonic acid metabolism and prostaglandin E2 production in amnion. Amnion cells were incubated with carbon 14-labeled arachidonic acid, and after various times the distribution of radiolabeled arachidonic acid in the lipids of these cells were determined. After incubation for 72 hours, 91% of the total radiolabeled arachidonic acid incorporated into cellular lipids was present in glycerophospholipids, and 9% was present in neutral lipids. The formation of [14C]prostaglandin E2 from [14C]arachidonic acid was maximal after 8 hours. In these studies the effect of human fetal urine on arachidonic acid metabolism in these cells was investigated (the production of prostaglandin E2 by amnion cells is increased by treatment with fetal urine). In cells incubated with [14C]arachidonic acid in the incubation medium, treatment with fetal urine for 4 hours caused a threefold to fourfold increase in [14C]prostaglandin E2 production, yet there were no detectable differences in the content of [14C]arachidonic acid in specific glycerophospholipids or neutral lipids of the cells after such treatment. In other studies, amnion cells were preincubated for 72 hours with [14C]arachidonic acid, and thereafter the cells were treated with fetal urine for 24 hours. With fetal urine treatment the amount of [14C]arachidonic acid in triacylglycerols decreased significantly compared with that in nontreated cells, but the formation of [14C]prostaglandin E2 was not increased. Thus we suggest that in response to fetal urine, prostaglandin E2 is formed from arachidonic acid that is released from a highly specific, stimulus-sensitive lipid pool or else from arachidonic acid that is derived from extracellular sources.

Amnion↗
PubMed1986

Prostaglandin E2 9-ketoreductase activity in human decidua vera tissue.

Amnion is believed to be a tissue of central importance in the biochemical processes of parturition. In this tissue, prostaglandin E2 is the near exclusive prostaglandin produced. And although the production of prostaglandin E2 is increased during labor in women, the levels of the major metabolite of prostaglandin E2 in maternal plasma are not elevated; rather, the levels of 13,14-dihydro-15-ketoprostaglandin F2 alpha, the major circulating metabolite of prostaglandin F2 alpha, are increased strikingly. Because of this apparent paradox, we considered the possibility that prostaglandin E2, originating in amnion, chorion laeve, or decidua vera, is converted to prostaglandin F2 alpha in decidua vera by the action of prostaglandin E2-9-ketoreductase. We found that prostaglandin E2 9-ketoreductase, the enzyme that catalyzes the conversion of prostaglandin E2 to F2 alpha, is present in cytosolic fractions prepared from homogenates of uterine decidua vera tissue. The specific activity of 9-ketoreductase in cytosolic fractions of decidua of six women varied from 3.2 to 155 pmol X min-1 X mg-1 protein. We also evaluated the conversion of exogenous prostaglandin E2 to F2 alpha in intact human endometrial stromal cells in monolayer culture. We found that prostaglandin E2, added to the culture medium, was converted to prostaglandin F2 alpha by endometrial stromal cells that were maintained in the presence of inhibitors of prostaglandin synthase. The extent of conversion of exogenous prostaglandin E2 to F2 alpha, however, was low relative to the specific activity of prostaglandin E2 9-ketoreductase found in decidual cytosol. These findings are consistent with the possibility that prostaglandin E2 formed in decidua vera tissue may be converted in that tissue to prostaglandin F2 alpha by 9-ketoreductase; on the other hand, prostaglandin E2 formed in contiguous tissues probably is not converted significantly to prostaglandin F2 alpha by decidual 9-ketoreductase.

Cytosol↗
PubMed1986

Prostaglandin secretion by adrenal tissue of human anencephalic fetuses.

Previously we reported that the human fetal adrenal gland secreted various prostaglandins and that prostaglandin secretion was inhibited by endogenously synthesized glucocorticoids. Furthermore, we reported that the neocortex secreted larger quantities of prostaglandins than did fetal zone tissue and that the pattern of secretion of prostaglandins of the two zones differed. In the present investigation the rate and pattern of prostaglandin secretion by adrenal tissue of anencephalic fetuses were assessed and compared to either whole or separated zones of human fetal adrenal tissue. The rate of prostaglandin secretion into the culture medium was determined by measuring prostaglandin E2 or prostaglandin F2 alpha with use of specific radioimmunoassays in media collected at 24-hour intervals. The rate of prostaglandin E2 secretion by adrenal glands obtained from two anencephalic fetuses declined rapidly from 1.71 +/- 0.65 ng/mg-1 of protein per 24 hours and 0.82 +/- 0.46 ng/mg-1 of protein per 24 hours on day 1, respectively, to 0.36 +/- 0.03 and 0.12 +/- 0.04 ng/mg-1 of protein per 24 hours by the fifth day in culture. The rate and pattern of prostaglandin F2 alpha secretion by anencephalic tissue was similar to that of prostaglandin E2. The pattern of prostaglandin secretion by anencephalic adrenal tissue was similar to that observed in neocortex tissue, but the rate of prostaglandin secretion was less. When the rates of prostaglandin secretion by anencephalic and neocortex adrenal tissue were compared to the rates of secretion of cortisol, an inverse relationship was observed. Finally, when whole human fetal adrenal glands or anencephalic tissues were incubated in the presence of adrenocorticotropic hormone, dexamethasone, metyrapone, or SU 10603, the data obtained seemed to suggest that the rate of prostaglandin secretion was regulated in both tissues by endogenously synthesized glucocorticosteroids. In summary, the pattern of secretion of prostaglandins by the anencephalic adrenal gland was similar to that of neocortex tissue, and the rate of secretion of prostaglandins was inhibited by endogenously synthesized cortisol.

Adrenal Cortex↗
PubMed1986

Glucocorticosteroid regulation of prostaglandin biosynthesis in human myometrial smooth muscle cells in monolayer culture.

In the present investigation, we evaluated the production of prostaglandins by human myometrial smooth muscle cells maintained in monolayer culture in the absence or presence of glucocorticosteroids. In the presence of cortisol (10(-7) M) or dexamethasone (10(-8) M), the rate of production of prostacyclin (PGI2) by these cells was decreased significantly. The glucocorticosteroid-mediated inhibition of prostaglandin production was attenuated when cortisol-21-mesylate (10(-6) M), a glucocorticosteroid antagonist, was present in the culture medium. The rate of conversion of radiolabeled arachidonic acid to radiolabeled prostaglandins as determined by use of sonicates of myometrial cells and optimal assay conditions, however, was not affected significantly by treatment with cortisol or dexamethasone in concentrations sufficient to inhibit prostaglandin formation by more than 80%. These findings are suggestive that glucocorticosteroids act in human myometrial smooth muscle cells in culture to inhibit prostaglandin formation by way of a receptor-mediated process that does not involve inhibition of enzyme activities that are involved in the biosynthesis of prostaglandins, i.e. the conversion of arachidonic acid to prostaglandin.

Arachidonic Acid↗
PubMed1986

Agarose as a tissue equivalent phantom material for NMR imaging.

Phantoms for evaluation of nuclear magnetic resonance (NMR) imaging systems were made from water-based agarose gels, according to a standard procedure herein described. Copper sulfate (CuSO4) was included in the gels to further affect their proton relaxation characteristics. The proton relaxation rates of each batch of gel are dependent on the concentrations of agarose and copper ions in it, with T1 depending more on copper than on agarose, and T2 depending more strongly on agarose than on copper. The wide range of T1 and T2 which can be covered, and the stability and physical characteristics of the agarose gel material make it well-suited for phantom use.

Copper↗
PubMed1986

Avascular necrosis of the hip: comparison of MR, CT, and scintigraphy.

The capabilities of MRI, radionuclide bone scanning, and X-ray CT in diagnosing avascular necrosis of the hip were compared in a controlled statistical study. Diagnostic ability was measured as the area under the receiver-operating-characteristic curve. Differences in efficacy among various case pools and the standard errors of those differences were calculated. MR was better than both other techniques over the entire case pool, with the difference between MR and radionuclide scanning exceeding 2 standard errors (p less than 0.01). In the subsample of patients including more early cases, MR was better than CT by greater than 2 standard errors and better than radionuclide scanning by over 3 standard errors. This is evidence that MR is the most sensitive imaging technique for the early diagnosis of avascular necrosis.

Adult↗
PubMed1986

Prostaglandin release following Nd:YAG iridotomy in rabbits.

In this study, iridotomies were performed in nine rabbit eyes using an Nd:YAG laser at 5.2 mJ, three pulses/burst, for one burst. Prostaglandin E2 (PGE2) in aqueous humor obtained at timed intervals after treatment was then measured using a sensitive and specific radioimmunoassay. Concentrations of PGE2 (mean +/- SD pg/ml) were: pretreatment, 377 +/- 89; 30 minutes, 1858 +/- 241; 120 minutes, 735 +/- 308; and 240 minutes, 401 +/- 59, postoperatively. The release of PGE2 into the aqueous humor parallels the rise in intraocular pressure following Nd:YAG iridotomies in rabbits and thus may contribute to this phenomenon.

Animals↗
PubMed1985

Inhibition of arachidonic acid metabolism by antipyrine and 4-aminoantipyrine.

Antipyrine and 4-aminoantipyrine are used to determine uterine and umbilical blood flows. When administered in vivo, these compounds produce a decrease in uterine contracture activity and maternal uterine vein 13,14-dihydro-15-keto-prostaglandin F2 alpha concentrations. In this paper we report that they also inhibit in vitro activity of prostaglandin synthase in bovine seminal microsomes.

Ampyrone↗
PubMed1985

Endogenous stimulant of prostaglandin endoperoxide synthase activity in human amniotic fluid.

In this study we describe the discovery and characterization of a substance in human amniotic fluid that stimulates prostaglandin biosynthesis by a microsome-enriched preparation of bovine seminal vesicles. The stimulatory activity is not retained substantially upon anisotropic ultrafiltration through a filter with a molecular weight exclusion limit of 500. Stimulation of prostaglandin biosynthesis by this substance is time- and concentration-dependent; maximal stimulation of approx. 200% being observed within 20 min of commencing incubation with 1 ml-equivalent of stimulant fraction. Stimulatory activity is demonstrable both in the presence of reduced glutathione (1.3 mM) and L-tryptophan (20 mM), either separately or combined, and in the presence of exogenous arachidonic acid (5-120 microM). In the absence of added cofactors, the stimulatory substance increases the rates of biosynthesis of prostaglandin E2 and prostaglandin F2 alpha to equal extents. The amount of stimulatory substance added to incubations is correlated positively with increased oxygen consumption during incubations. The stimulatory substance is stable to heating at 100 degrees C for 10 min but is inactivated substantially (to less than 20% of original activity) by treatment with pronase. It is concluded that human amniotic fluid contains a substance of relatively low molecular weight, which is proteinaceous in character, that stimulates prostaglandin endoperoxide synthase activity.

Amniotic Fluid↗
PubMed1985

Prostaglandins in the fetal circulation following maternal ingestion of a prostaglandin synthetase inhibitor during mid-pregnancy.

To assess the possible effect upon the fetus of maternal ingestion of the prostaglandin synthetase inhibitor, mefenamic acid, taken during mid-pregnancy (15-22 weeks) to prevent spontaneous abortion, samples of fetal blood were collected at fetoscopy from 13 treated and 14 untreated control cases. Mefenamic acid levels in the fetus were 32-54% of those in the mothers in the treated group, while prostaglandins E2 (PGE2), 6-oxo-PGF1 alpha and PGFM were all slightly but not significantly lower in those patients given 500 mg mefenamic acid 40-180 min prior to sampling than in untreated controls. Results indicate that the prostaglandin synthetase inhibitor crosses the placenta at this early gestation and may possibly suppress fetal prostaglandin production.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Prostaglandin biosynthesis stimulatory and inhibitory substances in human amniotic fluid during pregnancy and labor.

Human amniotic fluid has been separated into two fractions; one fraction inhibits prostaglandin biosynthesis and the other fraction is stimulatory. The activity of the stimulatory fraction increased with increasing gestational age and was greater still during labor. The activity of the inhibitory fraction decreased with increasing gestational age and was smaller still during labor. We speculate that these changes may play a significant role in parturition.

Amniotic Fluid↗
PubMed1985

Despite a massive increase in cortisol secretion in women during parturition, there is an equally massive increase in prostaglandin synthesis. A paradox?

In this investigation, we sought to resolve the apparent paradox that is posed by the fact that there is a simultaneous increase in the production of prostaglandin and cortisol in women during labor. A paradox obtains, since in most tissues, cortisol acts to inhibit prostaglandin formation. Using previously characterized model systems for the in vitro study of arachidonic acid metabolism in amnion, decidua, and myometrium, we found that prostaglandin production by amnion and endometrial stromal cells in monolayer culture was not decreased by glucocorticosteroid treatment. On the other hand, prostaglandin production by myometrial smooth muscle cells in culture was inhibited by greater than 90% in response to dexamethasone (10(-7) M) treatment. Importantly, the major prostaglandin produced by myometrium, as well as myometrial smooth muscle cells in culture, is prostacyclin, a prostaglandin that acts to cause uterine quiescence. We suggest that the immunity of amnion and decidua to the action of glucocorticosteroids may allow for the accelerated production of prostaglandins E2 and F2 alpha, which act to cause myometrial contractions; simultaneously, glucocorticosteroid produced in large quantities in women in labor may lead to decreased production of prostacyclin by myometrium, thereby reducing uterine quiescence. In this coordinated manner, the uterine contractions that culminate in delivery of the fetus may proceed uninterrupted in the face of increased cortisol production.

Amnion↗
PubMed1985

In vitro prostacyclin production by ovine uterine and systemic arteries. Effects of angiotensin II.

Normal pregnancy is associated with reduced systemic pressor responses to infused angiotensin II (ANG II); furthermore, the uterine vascular bed is even less responsive to vasoconstriction by ANG II than the systemic vasculature overall. The mechanism(s) for this refractoriness remains unknown. To determine if vessel production of prostacyclin may be responsible, uterine and omental artery segments were obtained from four groups of sheep, nonpregnant (NP), pregnant (P; 131 +/- 4 d), early postpartum (2.2 +/- 0.4 d), and late postpartum (16 +/- 2 d), and incubated in Krebs-Henseleit alone or with ANG II in the absence or presence of Saralasin. Prostacyclin was measured as 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha). Synthesis of 6-keto-PGF1 alpha was de novo, since aspirin inhibited its formation. P and early uterine arteries produced more 6-keto-PGF1 alpha than NP and late vessels (P less than 0.05): 386 +/- 60 (X +/- SE) and 175 +/- 23 vs. 32 +/- 5 and 18 +/- 4 pg/mg X h, respectively. A similar relationship was observed for omental arteries: 101 +/- 14 and 74 +/- 14 vs. 36 +/- 10 and 22 +/- 4 pg/mg X h, respectively. Furthermore, synthesis by arteries from P and early animals was greater in uterine than omental vessels (P less than 0.05); this was not observed in NP or late vessels. ANG II increased 6-keto-PGF1 alpha production 107 +/- 20% and 92 +/- 16% in P and early uterine arteries only; the threshold dose was between 5 X 10(-11) and 5 X 10(-9) M ANG II. This ANG II-induced increase in 6-keto-PGF1 alpha by uterine arteries was inhibited by Saralasin, which by itself had no effect. During pregnancy, the reduced systemic pressor response to ANG II and the even greater refractoriness of the uterine vascular bed may be reflective of vessel production of the potent vasodilator, prostacyclin. Furthermore, in the uterine vasculature, this antagonism may be potentiated by specific ANG II receptor-mediated increases in prostacyclin.

6-Ketoprostaglandin F1 alpha↗
PubMed1985

Experimental investigations of intraocular eicosanoids: cultured human trabecular cells and laser photocoagulation of the rabbit iris.

The significance of prostaglandins and other eicosanoids in normal ocular physiology and in ocular disease is not well understood. We have utilized cultured human trabecular cells and an in vivo model of laser-induced inflammation in the rabbit eye to gain information concerning eicosanoid biosynthesis and its regulation in the anterior segment. Further investigations using these experimental paradigms should help to elucidate the physiologic and pathophysiologic roles of eicosanoids in the eye.

Adolescent↗