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Biomedical subjects

D A Cox

Publications and source records attributed to D A Cox.

At least 37 records · Page 2Linked to original sources
PubMed1999

Bradykinin and phorbol ester but not 5-HT2B receptor activation stimulate phospholipase D activity in the rat stomach fundus.

1. Serotonin has been implicated as a mediator involved in migraine headache, an effect that may involve central 5-HT2B receptor activation. 5-HT2B receptor signal transduction in controversial. 2. Rat stomach fundus contraction to serotonin has been used as a model for 5-HT2B receptor activation. Serotonin-induced contractility involves intracellular calcium release and activation of protein kinase C without stimulation of phosphoinositide (PI) hydrolysis. 3. Since phospholipase D (PLD) activation results in phosphatidic acid production, which can release intracellular calcium and provide diacylglycerol for PKC activation, the purpose of this study was to determine whether the 5-HT2B receptor coupled to PLD activation using the rat stomach fundus as a model system. 4. Using phosphatidylethanol production to measure PLD activity, both bradykinin (0.01-1 microM) and phorbol dibutyrate (PDBu, 1 microM) stimulated PLD activity in rat stomach fundal strips, indicating that this tissue possesses an active PLD system. 5. Under identical conditions, 5-hydroxytryptamine (5-HT) failed to stimulate PLD activity over a concentration range (1 nM-1 microM) documented to induce 5-HT2B receptor-mediated contraction in rat stomach fundus. Thus, the 5-HT2B contractile receptor in rat stomach fundus is not coupled to PLD activation, whereas both bradykinin and phorbol ester do couple to PLD.

Animals↗
PubMed1999

Raloxifene hydrochloride, a selective estrogen receptor modulator: safety assessment of effects on cognitive function and mood in postmenopausal women.

Raloxifene hydrochloride (HCl) is a selective estrogen receptor modulator with estrogen agonist effects on bone and lipid metabolism and estrogen antagonist effects on reproductive tissues. Animal studies suggest that raloxifene may affect brain function as well, although the effects of raloxifene on the human brain remain to be established. This paper presents an early safety assessment of raloxifene effects on cognition and mood in postmenopausal women participating in a randomized, double-blind osteoporosis treatment trial. Psychometric test batteries were administered to postmenopausal women at baseline and 1, 6, and 12 months after initiating treatment with raloxifene (60 and 120 mg/day). The Memory Assessment Clinics (MAC) battery and Walter Reed Performance Assessment Battery (PAB) were used to assess multiple and independent aspects of cognitive function, while mood was assessed with the Geriatric Depression Scale (GDS). After 12 months of treatment, there were no significant differences between the raloxifene groups and placebo on performance in either the MAC battery or the PAB. The only significant difference observed was a slight increase in performance favoring the raloxifene 120 mg/day group in an assessment of verbal memory on the MAC battery after 1 month of treatment. Scores on the GDS and the self-reported incidence of mood-related events were not different between treatment groups at any of the assessment periods. These data do not suggest that raloxifene impairs cognition or affects mood in postmenopausal women treated for 1 year. Studies to further assess the safety and potential efficacy of raloxifene with respect to cognitive function are ongoing.

Adult↗
PubMed1998

Hormone and nonhormone therapy for the maintenance of postmenopausal health: the need for randomized controlled trials of estrogen and raloxifene.

Multiple health benefits have been postulated for the long-term use of hormone therapy in postmenopausal women, most notably for prevention of osteoporotic fractures and coronary heart disease, as well as several risks, including cancer of the breast and uterus and venous thromboembolism. Cardiovascular disease is the most common cause of death among postmenopausal women. If real, the reduction in risk of coronary heart disease by hormone use suggested by observational studies would likely outweigh the risks. The decision to initiate and maintain hormone therapy is complicated by uncertainties about estrogen's true benefits and risks. Raloxifene, a selective estrogen receptor modulator (SERM), appears to have many of the benefits of estrogen without the cancer risks. It is not known if SERMs can provide significant cardiovascular protection. This article reviews the relation of use of postmenopausal hormones and raloxifene to women's health and addresses the need for large randomized trials to quantify the effect of both postmenopausal estrogen and raloxifene on cardiovascular health.

Cardiovascular Diseases↗
PubMed1998

Enhanced expression of transforming growth factor-beta type I and type II receptors in wound granulation tissue and hypertrophic scar.

In the present study we have analyzed and compared, by immunohistochemistry and in situ hybridization, the expression pattern of the R4/ALK5 transforming growth factor (TGF)-beta type I receptor (RI) and the TGF-beta type II receptor (RII) in normal human skin, in wounded skin at various stages during the transition of wound granulation tissue to scar, and in long-persisting post-burn hypertrophic scars. In normal human skin, expression of RI and RII was clearly visible in the epidermis, in epidermal appendages, and in vascular cells, although only a small number of dermal fibroblasts revealed detectable levels of TGF-beta receptor expression. In contrast, granulation tissue fibroblasts showed strong expression of both TGF-beta receptor types, although in normal-healing excisional wounds their density decreased during granulation tissue remodeling. However, in post-burn hypertrophic scars, RI- and RII-overexpressing fibroblasts were found in high densities up to 20 months after injury. From these findings we suggest that the repair process of deep wounds involves the transformation of a subset of fibroblastic cells toward an increased TGF-beta responsiveness and a transient accumulation of these cells at the wound site. In addition, our study provides evidence that excessive scarring is associated with a failure to eliminate TGF-beta receptor-overexpressing fibroblasts during granulation tissue remodeling, which leads to a persistent autocrine, positive feedback loop that results in over-production of matrix proteins and subsequent fibrosis.

Actins↗
PubMed1997

Amyloid beta-induced neurotoxicity is associated with phospholipase D activation in cultured rat hippocampal cells.

The role of phospholipase D (PLD) in amyloid beta (Abeta)-induced neurotoxicity was studied by comparing the effects of Abeta (1-40) on PLD activity and release of lactate dehydrogenase (LDH) from cultured rat hippocampal cells. PLD activity was determined in [3H]myristic acid-labeled cells by measuring the formation of [3H]phosphatidylethanol in the presence of ethanol (0.5%), and LDH activity in the cell media was measured via colorimetric assay. Abeta (50 microM), aged for 3 days to allow for peptide aggregation, acutely (1 h) stimulated PLD activity. Unaged Abeta (50 microM) had no acute (1 h) effect on PLD activity, but significantly stimulated PLD activity by 87% when incubated with cells for 1-3 days. Abeta (50 microM)-induced PLD activity was closely correlated with Abeta (50 microM)-induced LDH release over a time course of 1-3 days. These data suggest that PLD activation may be involved in Abeta-induced neurotoxicity.

Amyloid beta-Peptides↗
PubMed1997

Transforming growth factor beta 3 (TGF beta 3) accelerates wound healing without alteration of scar prominence. Histologic and competitive reverse-transcription-polymerase chain reaction studies.

BACKGROUND: Transforming growth factor (TGF) beta 3 is a new isoform of the TGF beta superfamily and is presumed to play an important role in wound repair and scarring. OBJECTIVE: To examine the effects of TGF beta 3 on wound healing and on reducing scarring. DESIGN AND INTERVENTIONS: Dermal ulcers were created on the ears of 75 anesthetized young female rabbits. Either TGF beta 3 or vehicle was applied topically to the wounds. Wounds were bisected and analyzed histologically at postwounding day 7. A second group of wounds was treated with topical TGF beta 3 and TGF beta 2 or vehicle at days 0 and 3 and harvested at days 21 through 42 as an excessive scarring model. The third group of wounds was treated with TGF beta 1, TGF beta 2, and TGF beta 3 and vehicle. The granulation tissue was harvested at day 7, and cellular RNA was extracted for performing competitive reverse-transcription polymerase chain reaction. MAIN OUTCOME MEASUREMENT: The amount of new epithelium and granulation tissue was measured in TGF beta 3- and vehicle-treated wounds. The hypertrophic index was calculated for scarring wounds treated with TGF beta 2 and TGF beta 3 or vehicle. Levels of TGF beta 1 messenger RNA were measured in those wounds that were treated with TGF beta 1, TGF beta 2, and TGF beta 3 and in their controls. RESULTS: The use of TGF beta 3 (0.3-0.75 microgram per wound) increased granulation tissue formation by more than 100% (P < .005). Epithelialization showed a biphase, either increasing 30% (P < .04) or decreasing 25% (P < .001) dependent on dose. No significant difference in the hypertrophic index was noted in TGF beta 3-treated wounds compared with controls. Levels of TGF beta 1 messenger RNA increased (7.1- to 14.9-fold) in those wounds treated with TGF beta s compared with controls at day 7. CONCLUSIONS: Exogenous TGF beta 3 displays substantial vulnerary properties in wound healing and may be useful in treating nonhealing wounds. However, the observation that TGF beta 3 can reduce scarring was not confirmed in this study, and the messenger RNA level in response to TGF beta 3 suggests that it behaves similarly to TGF beta 1.

Animals↗
PubMed1997

Influence of gender on vasomotor effects of oxidized low-density lipoprotein in porcine coronary arteries.

This study compared 5-hydroxytryptamine (5-HT)-induced contraction and relaxation in coronary arteries from male and female pigs and compared the vasomotor effects of the atherosclerotic lipoprotein, oxidized low-density lipoprotein (LDL), in these tissues. 5-HT-induced contraction and endothelium-dependent relaxation were similar, as was sodium nitroprusside-induced relaxation, in coronary arteries from male and female pigs. These data suggest that there were no gender-related differences in 5-HT-induced contraction or 5-HT-mediated nitric oxide (NO) release from the coronary endothelium. In contrast, oxidized LDL (100 micrograms/ml) enhanced 5-HT-induced contraction to a greater extent in coronary arteries from male versus female pigs. Because oxidized LDL inhibited 5-HT-induced relaxation similarly in arteries from male and female animals, a greater effect of oxidized LDL on agonist-induced NO release in tissues from male pigs cannot explain the greater effect on 5-HT-induced contraction. Oxidized LDL contracted coronary arteries from males with a greater force than arteries from females when measured from baseline tone, suggesting that oxidized LDL inhibited basal NO release to a greater extent in coronary arteries from male pigs compared with females, an effect that may have participated in the greater enhancement of 5-HT-induced contraction that occurred in arteries from male pigs. These gender-related differences in the vasomotor effects of oxidized LDL may play an important role in the lesser incidence of cardiovascular disease in premenopausal females than in males and may provide insight into the cardioprotective effect of estrogen.

Animals↗
PubMed1997

Relationship between phospholipase D activation and endothelial vasomotor dysfunction in rabbit aorta.

Lysophosphatidylcholine (lysoPC) causes endothelial vasomotor dysfunction in isolated blood vessels, although the signaling pathways involved in this effect remain to be established. Although lysoPC stimulated phospholipase D (PLD) activity in cultured endothelial cells, the role of PLD in the vascular effects of lysoPC remains unclear. This study investigated the hypothesis that PLD is involved in lysoPC-induced endothelial vasomotor dysfunction in isolated rabbit aorta. LysoPC (3-30 microM) stimulated vascular PLD activity and inhibited endothelium-dependent vasorelaxation to acetylcholine within an identical concentration range. In contrast, lysoPC-induced inhibition of vasorelaxation was not prevented by the selective protein kinase C (PKC) inhibitor, GF109203X (3 microM), which suggested that this enzyme was not involved in the endothelial vasomotor dysfunction produced by lysoPC. The ability of two other lysophospholipids, lyso-platelet-activating factor (3-30 microM) and lysophosphatidylserine (10-30 microM) to induce endothelial vasomotor dysfunction was also associated closely with their ability to stimulate vascular PLD activity. Parallel stimulation of PLD activity and inhibition of acetylcholine-induced relaxation was also observed with orthovanadate (0.1-3 mM), which suggested that the association between PLD activation and endothelial vasomotor dysfunction was not a phenomenon particular to lysophospholipids. The magnitude of PLD stimulation and the extent of endothelial dysfunction induced by these diverse stimuli were highly correlated (r2 = 0.88). These observations suggest that the PLD signal transduction pathway is important in the endothelial vasomotor dysfunction produced by lysophospholipids and perhaps other agents.

Animals↗
PubMed1996

The crystal structure of TGF-beta 3 and comparison to TGF-beta 2: implications for receptor binding.

Transforming growth factors beta belong to a group of cytokines that control cellular proliferation and differentiation. Five isoforms are known that share approximately 75% sequence identity, but exert different biological activities. The structure of TGF-beta 3 was solved by X-ray crystallography and refined to a final R-factor of 17.5% at 2.0 A resolution. Comparison with the structure of TGF-beta 2 (Schlunegger MP, Grütter MG, 1992, Nature 358:430-434; Daopin S, Piez KA, Ogawa Y, Davies DR, 1992, Science 257:369-373) reveals a virtually identical central core. Differences exist in the conformations of the N-terminal alpha-helix and in the beta-sheet loops. In TGF-beta 3, the N-terminal alpha-helix has moved approximately 1 A away from the central core. This movement can be correlated with the mutation of Leu 17 to Val and Ala 47 to Pro in TGF-beta 3. The beta-sheet loops rotate as a rigid body 9 degrees around an axis that runs approximately parallel to the dimer axis. If these differences are recognized by the TGF-beta receptors, they might account for the individual cellular responses. A molecule of the precipitating agent dioxane is bound in a crystal contact, forming a hydrogen bond with Trp 32. This dioxane may occupy a carbohydrate-binding site, because dioxane possesses some structural similarity with a carbohydrate. The dioxane is in contact with two tryptophans, which are often involved in carbohydrate recognition.

Amino Acid Sequence↗
PubMed1996

5-HT2B receptor signaling in the rat stomach fundus: dependence on calcium influx, calcium release and protein kinase C.

The rat stomach fundus is enriched with the 5-hydroxytryptamine (5-HT)2B receptor, a recently cloned subtype of the 5-HT2 receptor family. Unlike other members of the 5-HT2 receptor family, the 5-HT2B receptor in the rat stomach fundus was not coupled to phosphatidylinositol (PI) hydrolysis. The purpose of this study was to characterize further the signal transduction mechanism of the 5-HT2B receptor in rat stomach fundus. Nitrendipine (1 microM) inhibited the maximal contraction to 5-HT (10 microM) by approx. 60%. 5-HT contractions were inhibited by approximately the same magnitude in the absence of extracellular calcium as in the presence of nitrendipine, indicating that calcium influx through voltage-dependent calcium channels accounted fully for the dependence of the 5-HT contraction on extracellular calcium. Depletion of both extracellular calcium and intracellular calcium stores abolished 5-HT contraction. Ryanodine (30 microM), an inhibitor of calcium release from internal stores, inhibited significantly the nitrendipine-insensitive 5-HT contraction, suggesting that this component of the contraction was due to calcium release from a ryanodine-sensitive site. Bisindolylmaleimide (5 microM), a specific inhibitor of protein kinase C (PKC), inhibited 5-HT contraction in either the absence or presence of nitrendipine, suggesting that activation of PKC is also important. Taken together, these data indicate that the 5-HT2B contractile receptor in the rat stomach fundus is coupled to calcium influx through voltage-dependent calcium channels, intracellular calcium release, and activation of PKC. These actions may reflect a novel coupling mechanism unrelated to increases in PI hydrolysis.

Animals↗
PubMed1996

Lysophosphatidylcholine stimulates phospholipase D in human coronary endothelial cells: role of PKC.

Lysophosphatidylcholine (lyso PC) mediates multiple potentially atherogenic effects on endothelial cells, although the cellular mechanism of these effects remains unclear. Phospholipase D (PLD) has been recognized as a novel second-messenger system that may regulate cellular function. The purpose of this study was to determine the effect of lyso PC on PLD activity in human coronary artery endothelial cells (HCAEC) by measuring [3H]phosphatidylethanol production in cells labeled with [3H]myristic acid. After incubation with lyso PC (20 microM) for 40 min, PLD activity was markedly stimulated from five- to sixfold. Stimulation of PLD activity by lyso PC was concentration dependent (half-maximum effective concentration of 7.6 microM) and was not mimicked by phosphatidylcholine (20 microM). Because PLD can be regulated by protein kinases, the effect of several protein kinase inhibitors on lyso PC-stimulated PLD activity was tested. The protein kinase A inhibitor H-89 (300 nM) and the tyrosine kinase inhibitors genistein (30 microM) and tyrphostin A25 (100 microM) had no effect on the stimulation of PLD by lyso PC (20 microM). The protein kinase C (PKC) inhibitor calphostin C (10-300 nM) affected neither lyso PC (20 microM)-nor 4 beta-phorbol 12,13-dibutyrate (PDBu, 300 nM)-stimulated PLD activity, suggesting that this agent may not inhibit PKC in these cells. In contrast, the selective PKC inhibitors GF-109203X (0.3-10 microM) and chelerythrine (1-30 microM) concentration dependently inhibited lyso PC (20 microM)-stimulated PLD activity and blocked PDBu (300 nM)-stimulated PLD activity. Together, these data document that lyso PC stimulated PLD in human endothelial cells, possibly by a PKC-dependent mechanism, and provide evidence that PLD activation in human endothelium is a novel and important mechanism by which lyso PC mediates its cellular and possibly atherogenic effects.

Alkaloids↗
PubMed1996

Neomycin selectively inhibits 5-hydroxytryptamine-induced contraction in the guinea pig trachea.

Neomycin (3 mM) inhibited maximal 5-HT-induced contraction by approximately 50% without inhibiting [3H]5-HT binding to 5-HT2A receptors. In contrast, neomycin had no effect on carbamylcholine- or histamine-induced contraction. Carbamylcholine (10 microM) and histamine (10 microM) both stimulated phosphatidylinositol (PI) hydrolysis but neomycin had no effect on the increase in PI hydrolysis. 5-HT (10 microM) did not stimulate PI hydrolysis in the absence or presence of neomycin, suggesting that neomycin inhibited 5-HT contraction in the guinea pig trachea independent of PI turnover. Although bradykinin stimulated phospholipase D (PLD) activity, 5-HT did not activate PLD, suggesting that the 5-HT2A receptor is not coupled to this enzyme in the guinea pig trachea. Neomycin (3 mM) and nitrendipine (1 microM) inhibited 5-HT-induced contraction to a similar extent, and neomycin did not further inhibit contraction in the presence of nitrendipine. These data indicate that neomycin inhibited 5-HT-induced contraction, like nitrendipine, via an effect on calcium influx through L-type calcium channels and did not affect intracellular calcium release. However, unlike nitrendipine which completely blocked KCl-induced contraction, neomycin only marginally reduced the maximal KCl-induced contraction. Taken together, these data suggest that neomycin may indirectly inhibit calcium influx through L-type calcium channels in guinea pig tracheal smooth muscle. The mechanism by which neomycin inhibited calcium influx in the guinea pig trachea may provide insight into the novel signaling pathway of the 5-HT2A receptor in this tissue.

Animals↗
PubMed1996

Effects of oxidized low-density lipoprotein on vascular contraction and relaxation: clinical and pharmacological implications in atherosclerosis.

Oxidized LDL exerts profound effects on the vasomotor response of isolated blood vessels to various stimuli that closely mimic the vascular dysfunction associated with hypercholesterolemia and atherosclerosis in humans. The beneficial effect of lipid-lowering therapy in normalizing vascular function and greatly decreasing the frequency of clinical events associated with atherosclerosis, combined with the ability of antioxidants to alleviate vasomotor disturbances in hypercholesterolemia and slow the progression of atherosclerosis, strongly support a causative role of oxidized LDL in mediating vascular dysfunction in vivo and contributing to the clinical sequalae of coronary artery disease. Further research to understand more fully the mechanisms of oxidized LDL formation and actions in vivo may reveal novel strategies to inhibit these events, and may prove beneficial in the therapeutic management of atherosclerotic disease.

Arteriosclerosis↗
PubMed1996

Selective enhancement of 5-hydroxytryptamine-induced contraction of porcine coronary artery by oxidized low-density lipoprotein.

Oxidatively modified low-density lipoprotein(LDL) may be involved in the vasomotor disturbances associated with hypercholesterolemia and atherosclerosis, but effects of this lipoprotein on agonist-induced coronary vasoconstriction have not been reported. This study determined the effects of oxidized LDL on contraction of isolated porcine coronary arteries to several contractile agonists and investigated the mechanism of these effects. Oxidized LDL (10-100 microgram/ml) enhanced 5-hydroxytryptamine (5-HT)-induced contraction in a concentration-dependent manner, whereas native LDL (100 microgram/ml) had no effect. Enhancement of 5-HT-induced contraction was dependent on the presence of endothelium and blocked by L-NG-monomethyl-arginine (100 microM). Oxidized LDL (100 microgram/ml) similarly inhibited endothelium- and nitric oxide-dependent relaxation induced by 5-HT, but had no effect of relaxation induced by sodium nitroprusside. Furthermore, contraction to U46619 and acetylcholine, agonists that did not mediate endothelium-dependent relaxation, was unaffected by oxidized LDL (100 microgram/ml). Lysophosphatidylcholine (10-30 mumol/liter) also enhanced 5-HT-induced contraction and inhibited 5-HT-induced, endothelium-dependent relaxation. Endothelium-dependent relaxation to bradykinin was unaffected by lysophosphatidylcholine (20 muM). Thus, oxidized LDL enhanced 5_HT-induced coronary vasoconstriction in an endothelium dependent manner, actions that were mimicked by relevant concentrations of lysophosphatidylcholine. These in vitro effects of oxidized LDL mimicked effects of hypercholesterolemia and atherosclerosis on 5-HT vasoactivity in human coronary arteries in vivo, suggesting that oxidized LDL may play an important role in the development of vasomotor disturbances in these pathologies.

Acetylcholine↗