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Biomedical subjects

C E Martin

Publications and source records attributed to C E Martin.

At least 55 records · Page 3Linked to original sources
PubMed1987

The effect of vitreous humour on prostaglandin production by cultured rabbit chorioretinal fibroblasts.

Factors in vitreous humour which regulate prostaglandin production were investigated using cultured rabbit chorioretinal fibroblasts. These cells produced predominantly prostaglandin E2, 6-ketoprostaglandin F1 alpha, a compound likely to be a metabolite of prostaglandin E2 and 5-hydroxyeicosatetraenoic acid. The synthesis of 6-ketoprostaglandin F1 alpha was nearly completely inhibited by the cyclooxygenase inhibitor aspirin and partially inhibited by 10(-6) M dexamethasone (49%) and 10(-5) M forskolin (68%). Addition of 10% rabbit vitreous humour to subconfluent cells maintained in Dulbecco's modified Eagle's medium plus 1% fetal bovine serum resulted in stimulation of 6-ketoprostaglandin F1 alpha production by as much as 246% as measured by radioimmunoassay. Chorioretinal fibroblasts labelled by [3H]arachidonic acid incorporation into cellular phospholipids synthesised greater amounts of all labelled arachidonic acid metabolites in response to vitreous humour. It was concluded, therefore, that there are factors present in vitreous humour of molecular weight above 10 kDa which are capable of stimulating cellular cyclooxygenase activity. Confluent cells also responded to a factor(s) present in vitreous humour. The fraction of less than 10 kDa inhibited 6-ketoprostaglandin F1 alpha production by 50% when used at a concentration of 10%. Furthermore, 6-ketoprostaglandin F1 alpha production in confluent cells (but not subconfluent cells) was inhibited to 40% of control levels by vitamin C at a concentration of 1 mg/100 ml. The latter result points to an inhibitory role for vitamin C in vitreous humour. We conclude, therefore, that vitreous humour contains factors important for the regulation of prostaglandin metabolism in the eye.

Animals↗
PubMed1986

Effects of Irradiance on Crassulacean Acid Metabolism in the Epiphyte Tillandsia usneoides L. (Bromeliaceae).

Spanish moss (Tillandsia usneoides L.) was collected in South Carolina, maintained in a greenhouse, then exposed to five levels of photosynthetic photon flux density (PPFD) for 3 weeks. Following this treatment, plants were sampled for chlorophyll concentrations, nocturnal acid accumulations, and photosynthetic responses to subsequent exposure at a range of PPFD. No acclimation to PPFD was observed; all plants exhibited similar patterns of nocturnal CO(2) uptake and acid accumulation regardless of initial PPFD treatment. These patterns revealed that at a PPFD level of approximately 200 micromoles per square meter per second (daytime integrated PPFD of 10 moles per square meter per day), CAM saturated or, in low-PPFD plants, was optimal. The results of this study indicate that adaptation to high PPFD is not necessarily a requirement of CAM.

Journal Article↗
PubMed1985

Human anti-luteinizing hormone-releasing hormone antibodies in patients treated with synthetic luteinizing hormone-releasing hormone.

One hundred sixty-three patients who were given synthetic LH-RH therapeutically underwent monitoring of serum IgG anti-LH-RH antibodies. Five of the patients showed specific binding to antibodies. Development of anti-LH-RH antibodies was not limited to those patients with a congenital deficiency of LH-RH. Urticarial responses occurred in four patients, only one of whom had IgG antibodies. Patients who had IgG antibodies or an urticarial response underwent monitoring of their serum IgE anti-LH-RH antibodies, but none had a positive binding response. The refractory state which has been reported in patients in whom similar antibodies to LH-RH develop was not invariably observed among these patients.

Adult↗
PubMed1985

Taxol for the treatment of proliferative vitreoretinopathy.

Proliferative vitreoretinopathy (PVR) results in retinal detachment and visual impairment due to fibroblastic proliferation in the vitreous and subsequent cellular contraction. The authors have used an in vitro model for PVR to evaluate the action of the antineoplastic drug, taxol, on chorioretinal fibroblast proliferation and contractility. Dose response curves obtained show taxol to be a potent inhibitor of both cellular events. Fifty percent inhibition of contraction and proliferation occurred at 2 X 10(-8)M and 3 X 10(-9)M, respectively. On the basis of this pharmacodynamic data, three dosage regimes were chosen to evaluate possible prevention of PVR in an animal model based on the intravitreal injection of cultured fibroblasts. These animals trials show that a single intravitreal dose of either 35 micrograms or 0.5 microgram taxol significantly reduces incidence and extent of PVR. The average grade of vitreoretinal traction at 28 days for 35 micrograms taxol and 250,000 cells was 0.4 (control 1.8); for 35 micrograms taxol and 700,000 cells, 1.0 (control 2.2); and for 0.5 microgram taxol and 250,000 cells, 1.0 (control 2.3). Delayed optic nerve damage was noted with the highest dose used, but a good therapeutic margin may exist. Long-term clinical histopathologic and electrophysiologic studies will be required. The authors conclude from these preliminary studies that taxol holds definite promise for the relief of traction retinal detachment and PVR.

Alkaloids↗
PubMed1984

Effect of cyclic AMP on cellular contractility and DNA synthesis in chorioretinal fibroblasts maintained in collagen matrices.

Dibutyryl cyclic AMP (db-cAMP), theophylline and forskolin were found to be potent inhibitors of DNA synthesis and cell contractility in chorioretinal fibroblasts maintained in 3-dimensional collagen matrices. Dose-response curves were constructed for the inhibitory action of these agents on both cellular parameters and their interrelationship examined by regression analysis. The results obtained indicate that these parameters were equally inhibited by cAMP with the exception of high concentrations of db-cAMP (greater than 10(-3) M) where a greater effect on DNA synthesis than cell contractility was observed which was attributed to additional inhibition of DNA synthesis by db-cAMP degradation products. It is proposed from the present results and those of other investigators that cAMP regulates non-transformed fibroblast proliferation and contraction through a common regulatory mechanism possibly involving cAMP-dependent protein kinases and calcium ions.

Animals↗
PubMed1983

Temperature-induced modifications of glycosphingolipids in plasma membranes of Neurospora crassa.

Plasma membranes isolated from a cell-wall-less mutant of Neurospora crassa grown at 37 and 15 degrees C display large differences in lipid compositions. A free sterol-to-phospholipid ratio of 0.8 was found in 37 degrees C membranes, while 15 degrees C plasma membranes exhibited a ratio of nearly 2.0. Membranes formed under both growth conditions were found to contain glycosphingolipids. Cultures grown at the low temperature, however, were found to contain 6-fold higher levels of glycosphingolipids and a corresponding 2-fold reduction of phospholipid levels. The high glycosphingolipid content at 15 degrees C compensates for the reduced levels of phospholipids in such a way that sterol/polar lipid ratios are almost the same in plasma membranes under the two growth conditions. Temperature-dependent changes in plasma-membrane phospholipid and glycosphingolipid species were also observed. Phosphatidylethanolamine levels were sharply reduced at 15 degrees C, in addition to a moderate increase in levels of unsaturated phospholipid fatty acids. Glycosphingolipids contained high levels of long-chain hydroxy fatty acids, which constituted 75% of the total fraction at 37 degrees C, but only 50% at 15 degrees C. Compositional changes were also observed in the long-chain base component of glycosphingolipids with respect to growth temperature. Fluorescence polarization studies indicate that the observed lipid modifications in 15 degrees C plasma membranes act to modulate bulk fluidity of the plasma-membrane lipids with respect to growth temperature. These studies suggest that coordinate modulation of glycosphingolipid, phospholipid and sterol content may be involved in regulation of plasma-membrane fluid properties during temperature acclimation.

Acclimatization↗
PubMed1983

Iron-binding proteins in vitreous humour.

The soluble protein composition of Macaque monkey vitreous humour was studied in order to understand its iron-binding properties. The protein content of vitreous humour was 217 micrograms/ml +/- 4.6%, 40% of which was serum albumin and 30% an iron-binding protein of hydrodynamic properties identical to that of transferrin or lactoferrin. Relative to serum, the vitreous humour contained a 13-fold excess of this protein(s). Isoelectric focusing, iron-binding and immunoelectrophoretic studies indicated that both vitreous humour and aqueous humour contained lactoferrin as well as serum transferrin. The iron-binding capacity of these proteins in vitreous humour was equivalent to the mass of haemoglobin iron contained in at least 570000 monkey erythrocytes. It was concluded that the intraocular lactoferrin originated from within the eye. These iron-binding proteins may play a protective role in ocular disturbances such as vitreous haemorrhage, iron foreign body toxicity and infection.

Animals↗
PubMed1983

Changes in fatty acid distribution and thermotropic properties of phospholipids following phosphatidylcholine depletion in a choline-requiring mutant of Neurospora crassa.

Growth of a choline requiring auxotroph of Neurospora crassa on medium lacking exogenous choline produces large changes in the levels of phosphatidylethanolamine and phosphatidylcholine. Whole cell fatty acid distributions were found to vary widely between different phospholipid species of normally growing, choline-supplemented cultures with phosphatidylcholine showing the highest levels of unsaturation and anionic phospholipids and cardiolipin having the lowest. In these lipids, choline deprivation produced little change in fatty acid profiles of phosphatidylethanolamine, whereas changes in fatty acids of phosphatidylcholine and acidic phospholipids resulted in increased levels of unsaturation at both growth temperatures. Microsomal phospholipids also showed fatty acid variability with sharp decreases in phosphatidylcholine unsaturates and increases in acidic phospholipid unsaturated fatty acids at low growth temperatures. Fluorescence polarization of 1,6-diphenylhexatriene in vesicles formed from total cellular and microsomal lipids showed that choline deprivation produces changes in thermotropic properties in the lipids in deprived cultures at either growth temperature. The effective differences in fluorescence polarization between choline-deprived and supplemented cultures grown at a given temperature were found to be comparable to those produced by temperature were found to be comparable to those produced by temperature acclimation in normally growing cultures over a temperature range of 22 K.

Choline↗
PubMed1983

C(3) Photosynthesis and Crassulacean Acid Metabolism in a Kansas Rock Outcrop Succulent, Talinum calycinum Engelm. (Portulacaceae).

The potential for Crassulacean acid metabolism (CAM) was investigated in the sandstone outcrop succulent Talinum calycinum in central Kansas. Field studies revealed CAM-like diurnal acid fluctuations in these plants. These fluctuations persisted under all moisture and temperature regimes in the laboratory. Despite this CAM-like acid metabolism, simultaneous gravimetric determinations of day- and nighttime transpiration rates indicated the presence of a C(3) gas exchange pattern. Subsequent analyses of diurnal CO(2) and H(2)O exchange patterns under well-watered conditions and after 3, 5, and 7 days of drought confirmed these findings, though low rates of nocturnal CO(2) uptake were observed on the fifth night after continuous drought. Finally, the delta(13)C/(12)C value of this succulent, -27.8 per thousand, emphasizes the insignificance of any nocturnal CO(2) uptake in the lifelong accumulation of carbon in this species. Thus, it is proposed that T. calycinum is a C(3) plant with some CAM characteristics, including the ability to re-fix respiratory CO(2) at night under all moisture regimes, potentially resulting in a conservation of carbon, and occasionally to fix atmospheric CO(2) at night. These findings may prove to be common among rock outcrop succulents.

Journal Article↗
PubMed1982

The effects of altered levels of phosphatidylcholine and phosphatidylethanolamine on fatty acid desaturase activity and sterol metabolism during temperature acclimation in a choline auxotroph of Neurospora crassa.

Experiments were conducted to determine the effects of choline deprivation on levels of phospholipid fatty acids in a choline auxotroph (chol-1; chol-2) of Neurospora crassa with respect to high (37 degrees C) and low (15 degrees C) growth temperatures and during acclimation following a shift from high to low temperature conditions. Although grossly altered levels of phosphatidylethanolamine and phosphatidylcholine were observed at both temperatures, phospholipid fatty acid levels remained virtually identical to those found in a phenotypically wild-type and maximally supplemented chol-1; chol-2 strains grown under the same conditions. Deprivation of choline from supplemented cultures of the mutant followed by a shift from high to low growth temperatures did not significantly affect the level of fatty acid desaturation with respect to control cultures. Free sterols did not significantly affect the level of fatty acid desaturation with respect to control cultures. Free sterols were reduced, however, and sterol ester levels were elevated in choline-deprived cultures, suggesting that sterol interconversions may be closely tied to aspects of phospholipid biosynthesis. These experiments suggest that although major modifications in membrane fluidity may be brought about by thermally induced changes in fatty acid desaturase activity, it seems probable that additional cellular mechanisms may be involved if fluidity is under precise control.

Acclimatization↗
PubMed1982

The effects of temperature acclimation on membrane sterols and phospholipids of Neurospora crassa.

Experiments were conducted to examine the effects of temperature acclimation on sterol and phospholipid biosynthesis in Neurospora crassa. Cultures grown at high (37 degrees C) and low (15 degrees C) temperatures show significant differences in free and total sterol content, sterol/phospholipid ratios and distribution of major phospholipid species in total lipids and two functionally distinct membrane fractions. The ratio of free sterols to phospholipids in total cellular lipids from 15 degrees C cultures was found to be about one-half that found at 37 degrees C, whereas sterol/phospholipid ratios of mitochondrial and microsomal membranes were found to be higher at the low growth temperature. Total sterol and phospholipid biosynthetic rates showed parallel reductions in cultures acclimating to a shift from 37 to 15 degrees C growth conditions. Distribution of [14C]acetate label into free sterols was significantly lower under these conditions, however; indicating an increase in the conversion rate of sterols to sterol esters at the lower temperature. Mitochondrial and microsomal membrane fractions showed distinct phospholipid distributions which also differed from total lipid distributions at the two growth temperatures. In each case there was a consistent decrease in phosphatidylcholine and a corresponding increase in phosphatidylethanolamine as growth temperatures were lowered.

Acclimatization↗
PubMed1982

Relationship of serum testosterone to sexual activity in healthy elderly men.

There are reports of decreases in both sexual activity and serum testosterone in older men but not of any clear association between the two variables. In healthy participants in the Baltimore Longitudinal Study on Aging, despite the fact that serum testosterone did not decline with age, sexual activity decreased in a highly predictable fashion. In men over 60 years old, those with higher levels of sexual activity (for age) had significantly greater levels of serum testosterone. Although we found an inverse correlation between testosterone and percentage of body fat, there was no relationship between percentage of body fat and sexual activity. We also found no correlation between testosterone or sexual activity and smoking or coronary heart disease. Subjects drinking more than 4 oz. of ethanol per day were more likely to have decreased sexual activity but not diminished testosterone concentration. Our data suggest that, although serum testosterone level and ethanol intake may affect sexual activity in older men to some degree, age itself still appears to be the most influential variable.

Aged↗
PubMed1981

Effects of temperature acclimation on Neurospora phospholipids. Fatty acid desaturation appears to be a key element in modifying phospholipid fluid properties.

Experiments were conducted on the effect of growth temperature on phospholipids of Neurospora. Strains grown at high (37 degrees C) and low (15 degrees C) temperatures show large differences in the proportions of phospholipid fatty acid alpha-linolenate (18 : 3) which can vary by 10-fold over this temperature range. Changes in the phospholipid base composition are less dramatic; the most significant is an increase in phosphatidylethanolamines at low temperatures accompanied by a concomitant decrease in phosphatidylcholine. It appears that phospholipid fatty acid desaturation is closely regulated with respect to growth temperature. Over the 37 to 15 degrees C growth temperature range there appear to be at least two desaturase systems in Neurospora which are under different controls. Production of 18 : 1 and 18 : 2 species appears to occur at high levels over the entire temperature range, whereas the production of 18 : 3 seems to be inversely related to growth temperature. Shifting 37 degrees C-acclimated cultures to 15 degrees C produces a growth lag period of approximately 3 h, during which the level of 18 : 3 increases markedly. Differential scanning calorimetry of phospholipids from 37 degrees C cells shows a phase transition at -22 degrees C while lipids from 15 degrees C cultures exhibit a phase transition with reduced enthalpy at about -41 degrees C. The data are consistent with the idea that phospholipid composition in Neurospora is under strict control and suggest that membrane fluidity is regulated with respect to growth temperature through changes in membrane lipid composition.

Acclimatization↗
PubMed1981

Factor affecting sexual functioning in 60-79-year-old married males.

In data obtained from interviews with 60-79-year-old, married uppermiddle-class males, frequency of sexual expression proved to be independent of such factors as marital adjustment, sexual attractiveness of wives, sexual attitudes, and demographic features of the marital history. However, former levels of sexual functioning, as revealed by retrospective inquiry, appeared as highly significant correlates of current functioning in accordance with the hypothesis that males generally maintain relatively high or low rates of sexual activity throughout their lives. Of particular interest was the finding that, in the male, sexual frequency, erotic responsiveness to visual stimuli, and time comfortable without sex are closely interrelated phenomena, suggesting that all three variables are strongly commensurate with degree of motivation. Finally, those subjects found to be less than fully potent at report were also found to be virtually free of performance anxiety, feelings of sexual deprivation, and loss of self-esteem. This is consistent with lack of motivation being responsible for lower sexual functioning.

Aged↗
PubMed1981

Crassulacean Acid Metabolism in the Epiphyte Tillandsia usneoides L. (Spanish Moss) : RESPONSES OF CO(2) EXCHANGE TO CONTROLLED ENVIRONMENTAL CONDITIONS.

Patterns of CO(2) exchange in Spanish moss under various experimental conditions were measured using an infrared gas analysis system. Plants were collected from a study site in North Carolina and placed in a gas exchange chamber for several days of continuous measurements. No substantial seasonal effects on CO(2) exchange were observed. High rates of nocturnal CO(2) uptake were observed under day/night temperature regimes of 25/10, 25/15, 25/20, 30/20, and 35/20 C; however, daytime temperatures of 40 C eliminated nighttime CO(2) uptake and a nighttime temperature of 5 C eliminated nocturnal CO(2) uptake, regardless of day temperature. Constant chamber conditions also inhibited nocturnal CO(2) uptake. Constant high relative humidity (RH) slightly stimulated CO(2) uptake while low nighttime RH reduced nocturnal CO(2) uptake.Reductions in daytime irradiance to approximately 25% full sunlight had no effect on CO(2) exchange. Continuous darkness resulted in continuous CO(2) loss by the plants, but a CO(2) exchange pattern similar to normal day/night conditions was observed under constant illumination. High tissue water content inhibited CO(2) uptake. Wetting of the tissue at any time of day or night resulted in net CO(2) loss. Abrupt increases in temperature or decreases in RH resulted in sharp decreases in net CO(2) uptake.The results indicate that Spanish moss is tolerant of a wide range of temperatures, irradiances, and water contents. They also indicate that high nighttime RH is a prerequisite for high rates of CO(2) uptake.

Journal Article↗