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J R Tippins

Publications and source records attributed to J R Tippins.

At least 19 recordsLinked to original sources
PubMed2001

Reactive oxygen species mediate endothelium-dependent relaxations in tetrahydrobiopterin-deficient mice.

(6R)-5,6,7,8-Tetrahydro-biopterin (H(4)B) is essential for the catalytic activity of all NO synthases. The hyperphenylalaninemic mouse mutant (hph-1) displays 90% deficiency of the GTP cyclohydrolase I, the rate-limiting enzyme in H(4)B synthesis. A relative shortage of H(4)B may shift the balance between endothelial NO synthase (eNOS)-catalyzed generation of NO and reactive oxygen species. Therefore, the hph-1 mouse represents a unique model to assess the effect of chronic H(4)B deficiency on endothelial function. Aortas from 8-week-old hph-1 and wild-type mice (C57BLxCBA) were compared. H(4)B levels were determined by high-performance liquid chromatography and NO synthase activity by [(3)H]citrulline assay in homogenized tissue. Superoxide production by the chemiluminescence method was measured. Isometric tension was continuously recorded. The intracellular levels of H(4)B as well as constitutive NO synthase activity were significantly lower in hph-1 compared with wild-type mice. Systolic blood pressure was increased in hph-1 mice. However, endothelium-dependent relaxations to acetylcholine were present in both groups and abolished by inhibition of NO synthase with N(G)-nitro-L-arginine methyl ester as well. Only in hph-1 mice were the relaxations inhibited by catalase and enhanced by superoxide dismutase. After incubation with exogenous H(4)B, the differences between the 2 groups disappeared. Our findings demonstrate that H(4)B deficiency leads to eNOS dysfunction with the formation of reactive oxygen species, which become mediators of endothelium-dependent relaxations. A decreased availability of H(4)B may favor an impaired activity of eNOS and thus contribute to the development of vascular diseases.

Acetylcholine↗
PubMed2000

Nippostrongylus brasiliensis: infection induces upregulation of acetylcholinesterase activity on rat intestinal epithelial cells.

Expression of cholines terases and muscarinic acetylcholine receptors in the jejunal mucosa has been investigated during infection of rats with the nematode parasite Nippostrongylus brasiliensis. Selective expression of m3 receptors was observed on epithelial cells from uninfected rats and animals 7 days postinfection, and saturation binding with [(3)H]quinuclidinyl benzilate indicated that receptor expression on cell membranes was unaltered by infection. Butyrylcholinesterase was highly expressed in mucosal epithelia, but acetylcholinesterase was present at low levels in uninfected animals. In contrast, discrete foci of intense acetylcholinesterase activity were observed on the basement membrane of intestinal epithelial cells in animals infected with N. brasiliensis. This was demonstrated to be due to upregulation of expression of endogenous enzyme, which peaked at Day 10 postinfection and subsequently declined to preinfection levels. It is suggested that this occurs in response to hyper-activation of the enteric nervous system as a result of infection, and may benefit the host by limiting excessive fluid secretion due to cholinergic stimulation.

Acetylcholinesterase↗
PubMed1999

The vasoconstrictor effect of 8-epi prostaglandin F2alpha in the hypoxic rat heart.

1. 8-epi prostaglandin (PG) F2alpha, a vasoconstrictor isoprostane, is synthesized under conditions of oxidative stress. This study was undertaken to investigate the vasoconstrictor effect of 8-epi PGF2alpha in the coronary circulation before and after a period of oxidative stress. 2. The effects of the isoprostane 8-epi PGF2alpha and the thromboxane mimetic U46619 were compared in the isolated rat heart perfused in the Langendorff mode at a constant pressure of 80 mmHg. 3. In normal hearts U46619 caused a dose-related reduction in coronary flow (ED50 4.7+/-2.2 nmol). In contrast, 8-epi PGF2alpha had no effect. 4. After reducing perfusion pressure to 20 mmHg for 30 min and reperfusing at 80 mmHg, the dose-response curve to U46619 was unaffected. In contrast, 8-epi PGF2alpha caused a dose-dependent drop in coronary flow (ED50 52.6+/-12.7 nmol), producing a similar maximal reduction to U46619. 5. Similarly, after perfusion with xanthine and xanthine oxidase for either 15 or 30 min there was little change in the response to U46619 in comparison to control hearts. In contrast, 8-epi PGF2alpha caused a reduction in coronary flow similar to that produced by U46619, the magnitude of the response being related to the length of xanthine/xanthine oxidase perfusion. 6. Responses to both U46619 and 8-epi PGF2alpha after xanthine/xanthine oxidase perfusion were blocked by the selective thromboxane receptor antagonist SQ29548 10(-7) M. 7. These results show that oxidative stress in the isolated perfused rat heart reveals a potent vasoconstrictor effect of the isoprostane 8-epi PGF2alpha by an action on the thromboxane receptor. 8. The data also suggest that, since 8-epi PGF2alpha is a partial agonist at the thromboxane receptor, thromboxane receptor reserve is increased by oxidative stress.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1998

Actions of 8 epi prostaglandin F2alpha on isolated rat aorta.

8-epi prostaglandin F2alpha(8-epi PGF2alpha) contracted rat thoracic aorta rings in a concentration-dependent manner in the presence or absence of functional endothelium [median effective concentration (EC50) values, 455+/-52 and 268+/-34 nM, respectively; Student's t test; p=0.006]. U46619 was a more potent agonist with or without functional endothelium (EC50 values, 6.8+/-1.6 and 4.5+/-1.0 nM, respectively). SQ29548 [a thromboxane (TP)-receptor antagonist] inhibited contractions to both 8-epi PGF2alpha and U46619 in a competitive manner, with mean pA2 values of 8.3 and 7.9, respectively. 8-Epi PGF2alpha had a further contractile effect in vessels that had been contracted with noradrenaline and had been shown to possess a functional endothelium. Inhibition of thromboxane synthesis with OKY-046 or blockade of endothelin receptors with bosentan had no effect on responses to 8-epi PGF2alpha or U46619. Preincubation with 8-epi PGF2alpha or noradrenaline shifted the concentration-response curves to U46619 upward at low concentrations of U46619 with no significant change in EC50 values or maximal responses. Reduction of TP-receptor number in rat aorta with dithiothreitol caused a concentration-dependent inhibition of responses to both U46619 and 8-epi PGF2alpha, with no effect on maximal responses and or on the responses to U46619 after the preincubation with 8-epi PGF2alpha. These results indicate that 8-epi PGF2alpha is a potent vasoconstrictor in the rat aorta and are suggestive of an action of 8-epi PGF2alpha at the TP receptor.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1998

Regional variations in endothelin-1 and its receptor subtypes in human coronary vasculature: pathophysiological implications in coronary disease.

Endothelin-1 is a potent vasoconstrictor peptide and mitogen for vascular smooth muscle cells. Increased plasma or tissue levels of endothelin-1 have been described after myocardial infarction and in atherosclerosis, suggesting that this peptide may play a pathophysiological role in various coronary syndromes. Here, we have studied regional variations in ET-1 and its receptors in control and atherosclerotic human coronary vasculature using standard immunohistochemistry and in vitro autoradiography. ET-1 immunoreactivity was associated with luminal endothelial cells and smooth muscle cells at regions of atherosclerosis. ET(A) receptors were present on smooth muscle cells of coronary arteries and on cardiac myocytes. Medial ET(B) receptor binding at the proximal region of coronary arteries was weak, but increased significantly towards distal regions of this vessel (p<0.005 in control and p<0.0005 in ischaemic heart disease). Microvascular endothelial cells in the adventitia of coronary arteries, myocardial microvessels and the endocardial endothelium expressed the ET(B) receptor exclusively. The receptor variations revealed in this study provide supporting evidence that ET-1 is associated with (1) vascular smooth muscle and endothelial cell proliferation, including areas of intimal hyperplasia and regions of neovascularization (2) increased ET-1-induced reactivity of distal portions of the human coronary artery, (3) ET-1-mediated constriction of myocardial microvessels. These results provide new insights into different potential roles for this peptide in healthy and diseased human coronary vasculature.

Autoradiography↗
PubMed1997

Hypothalamic hypertensive factor: an inhibitor of nitric oxide synthase activity.

Human and rat plasma and rat hypothalamus contain a cytochemically detectable substance, the concentration of which rises with an increase in salt intake. The plasma concentration of this material is also raised in essential hypertension and in the spontaneously hypertensive rat (SHR), the Milan hypertensive rat, and the reduced renal mass (RRM) hypertensive rat. In the normal rat, the greatest concentration is found in the hypothalamus of the SHR and the RRM hypertensive rat. The physicochemical characteristics of this cytochemically detectable hypothalamic hypertensive factor (HHF), including chromatographic behavior and molecular weight range, suggest that it may share features common to a substituted guanidine that is present in established nitric oxide synthase (NOS) inhibitors. It was therefore decided to determine the effect on NOS activity of the HHF obtained from mature SHR. The ability of HHF to inhibit NOS activity was studied on (1) NOS extracted from bovine aorta, rat brain, and human platelets by measuring the conversion of radiolabeled L-arginine to L-citrulline and (2) rat liver NOS measured indirectly with a cytochemical technique based on the stimulation of soluble guanylate cyclase activity in hepatocytes by NO. HHF showed a biphasic inhibitory action on platelet NOS activity that was greater with HHF obtained from SHR than from Wistar-Kyoto rats. HHF also had a biphasic inhibitory effect on hepatocyte NOS activity that was more potent when obtained from SHR. It is proposed that the increase in HHF, a novel form of NOS inhibitor that is elevated in SHR, may be involved in the rise in arterial pressure.

Animals↗
PubMed1996

Coronary artery constriction by the isoprostane 8-epi prostaglandin F2 alpha.

1. This study was undertaken to compare the effects of 8-epi prostaglandin F2 alpha (8-epi PGF2 alpha) to those of prostaglandin F2 alpha (PGF2 alpha) and U46619, a thromboxane mimetic, on ovine, bovine and porcine coronary arteries. 2. 8-epi PGF2 alpha constricted porcine and bovine coronary arteries in a concentration-dependent manner with EC50 values of 689.0 +/- 229.3 and 1361.0 +/- 272.3 nM, respectively, but had no effect on ovine coronary arteries. 3. U46619 was a potent vasoconstrictor of porcine, ovine and bovine coronary arteries with EC50 values of 33.0 +/- 23.5, 373.3 +/- 69.7 and 254.1 +/- 134.3 nM, respectively. Emax values were significantly greater than those obtained with 8-epi PGF2 alpha. 4. PGF2 alpha constricted procine and bovine coronary arteries in a concentration-dependent manner with EC50 values of 1631.0 +/- 207.6 and 3644.0 +/- 344.8 nM, respectively, but had no effect on ovine coronary arteries. 5. Concentration-dependent constriction to U46619 in porcine coronary arteries was competitively inhibited by SQ29548 (10(-8) M to 10(-7) M) and BM13505 (10(-8) M to 10(-6) M) with no decrease in maximal responses. 6. Concentration-dependent constriction to 8-epi PGF2 alpha in porcine coronary arteries was inhibited in a concentration-dependent manner by SQ29548 (10(-8) M to 10(-7) M) and BM13505 (10(-8) M to 10(-6) M). However, the inhibition was associated with a decrease in maximal response. 7. Maximal responses of porcine coronary artery to U46619 (1 microM) and 8-epi PGF2 alpha (30 microM) were inhibited in a concentration-dependent manner by SQ29548 with IC50 values 99 +/- 12.36 nM and 46.5 +/- 18.67 nM, respectively. 8. Although ovine coronary arteries did not constrict to 8-epi PGF2 alpha pre-incubation of these vessels with 8-epi PGF2 alpha caused a rightward shift of the U46619 response curve in a concentration-dependent manner. 9. Pre-incubation of porcine coronary arteries with 8-epi PGF2 alpha competitively inhibited responses to U46619 with a Schild slope of 0.99 and a pA2 of 6.13. 10. We conclude that 8-epi PGF2 alpha is a vasoconstrictor within porcine and bovine coronary arteries, with a potency approximately twice that of PGF2 alpha but 5-20 times lower than U46619. The data suggest that 8-epi PGF2 alpha is acting as a partial agonist on the TP-receptor in the coronary vasculature.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1995

[3H]bosentan binding to human coronary artery: functional correlates.

The binding characteristics and localization of bosentan, an orally active endothelin-1 (ET-1) antagonist, were studied on sections of human coronary artery by in vitro autoradiography. Competition studies were performed to determine the ability of bosentan to prevent [125I]ET-1 binding to the coronary vasculature. The effects of bosentan on ET-1-induced contraction of the coronary artery were also studied in vitro. [3H]Bosentan bound to the tunica media of the human coronary artery. Unlabeled bosentan prevented [125I]ET-1 binding to this vessel in a concentration-dependent manner, and functional studies indicated that bosentan antagonizes ET-1--induced constriction. These data show that bosentan is able to reduce ET-1 binding to the human coronary artery and ET-1 constrictor effects in vitro. Bosentan is an orally active ET-1 antagonist, and these results suggest that this compound might be used to block the effects of locally released ET-1 in pathologic conditions, such as atherosclerosis, angina, and myocardial ischemia.

Autoradiography↗
PubMed1992

WEB 2086 inhibits neutrophil dependent increases in coronary resistance in blood perfused rabbit heart.

OBJECTIVE: The aim was to investigate the mechanism of the pressor action of the chemotactic peptide formyl-methionyl-leucyl-phenylalanine in the blood perfused Langendorff preparation of the isolated rabbit heart; and in particular to establish whether the response was dependent on the presence of neutrophils and whether the release of platelet activating factor contributed to the pressor effect. METHODS: An isolated rabbit heart was perfused with blood from an anesthetised support rabbit. Formyl-methionyl-leucyl-phenylalanine was injected intra-arterially proximal to the isolated heart and measures of cardiac performance recorded. In some experiments the support animal was depleted of neutrophils by pretreatment with mechlorethamine while in others the specific platelet activating factor receptor antagonist WEB 2086 was given to the support animal before formyl-methionyl-leucyl-phenylalanine. Differential blood cell counts were determined throughout the course of each experiment. Each heart was examined histologically after the experiment. RESULTS: Formyl-methionyl-leucyl-phenylalanine caused a significant rise in perfusion pressure which was virtually abolished by leucocyte depletion of the support animal. The response could also be reduced by about 80% with intravenous WEB 2086. Histological examination of the perfused hearts showed that the number of accumulated neutrophils was very variable and not correlated with the rise in perfusion pressure. There was no significant difference between control hearts and those receiving WEB 2086. CONCLUSIONS: The results confirm previous reports that the response to formyl-methionyl-leucyl-phenylalanine is neutrophil dependent and show that this model of a blood perfused heart can be used successfully to examine the response to a leucocyte dependent stimulus. The results also suggest that the response to formyl-methionyl-leucyl-phenylalanine may not only be due to physical obstruction of the coronary circulation or "neutrophil plugging", but may also be due to the release of platelet activating factor.

Animals↗
PubMed1990

Structure-activity relationship of human calcitonin-gene-related peptide.

The calcitonin-calcitonin-gene-related peptide (CGRP) gene complex encodes a small family of peptides: calcitonin, CGRP and katacalcin. Calcitonin is a circulating hormone that prevents skeletal breakdown by inhibiting the resorption of bone by osteoclasts. CGRP, a potent vasodilator, is involved in normal regulation of blood flow. The calcitonins structurally resemble the CGRP peptides, and both are known to cross-react at each others' receptors. The present study was undertaken to examine the structural prerequisites for biological activity of the intact CGRP molecule. We therefore prepared eight chymotryptic and tryptic fragments of CGRP and synthesized its acetylated and S-carboxyamidomethylcysteinyl analogues. The analogues were purified by h.p.l.c. and their structures were confirmed by fast-atom bombardment mass spectrometry. We have examined the effects of structurally modified analogues and fragments of human CGRP in a calcitonin-receptor-mediated assay, the osteoclast bone resorption assay, and in one or two CGRP-receptor-mediated assays, the rabbit skin blood flow assay and the oedema formation assay. The results showed that (1) in the osteoclast bone resorption assay, both CGRP peptides, alpha and beta, were equipotent, and were both at least 1000-fold were both approx. 1000-fold more potent than salmon calcitonin; human calcitonin had no effect; (3) the bis- and N-acetylated CGRP analogues retained reduced levels of biological activity in all assays, whereas S-carboxyamidomethylcysteinyl-human CGRP was without activity; and (4) all tryptic and chymotryptic fragments of CGRP were without biological activity, with the exception of hCGRP-(Ala1-Lys35): this fragment had much reduced activity compared with the intact peptide in inhibiting osteoclastic bone resorption and increasing blood flow in the rabbit skin. The results suggest that: (1) calcitonin and CGRP act at distinct receptors to mediate different physiological effects; (2) minor amino acid substitutions, as between the alpha and beta forms of CGRP (these two forms have 94% structural similarity) do not result in differences in biological activity; (3) the intact peptide is required for full biological activity of the CGRP molecule, and even the loss of two amino acids at the C-terminus of the molecule results in a marked decrease in activity; (4) the disulphide bridge appears to play an important role in the interaction of the intact CGRP molecule with its receptor; and (5) the C-terminal region is probably necessary for the peptide to assume the right conformation in the interaction with the receptor.

Amino Acid Sequence↗
PubMed1989

The role of cyclic AMP in the inhibition of leukotriene biosynthesis by neuropeptides.

Certain neuropeptides, including vasoactive intestinal peptide, inhibit peptidoleukotriene release from platelet activating factor-stimulated rat lung. We have now shown that vasoactive intestinal peptide will also inhibit peptidoleukotriene release from platelet activating factor-stimulated or ovalbumin-challenged guinea pig lung, but not from calcium ionophore-stimulated rat or guinea pig lung. In rat lung a pre-incubation with the peptide prior to addition of platelet activating factor was required for the effect to be maximal. When vasoactive intestinal peptide was substituted with cyclic AMP, the inhibitory effect was reproduced. In addition, pre-incubation with MDL 12330A, an inhibitor of adenylate cyclase, reduced the inhibitory effect of vasoactive intestinal peptide on platelet activating factor-stimulated leukotriene C4 biosynthesis. We suggest that the inhibition of platelet activating factor-stimulated peptidoleukotriene release in rat lung by vasoactive intestinal peptide involves the events prior to phospholipase A2 activation and requires cyclic AMP as a mediator.

Animals↗
PubMed1989

The synthesis, release and action of leukotrienes in the isolated, unstimulated, buffer-perfused rat heart.

When the perfusion medium of an isolated, non-recirculating, Langendorff rat heart is changed from Krebs buffer to coronary effluent, a significant vasoconstriction (23%, P less than 0.005) is observed. In this study we have investigated the involvement of leukotrienes in this phenomenon. We have extracted and quantified leukotrienes C4, D4 and E4 in samples of coronary effluent taken at different times during the first 2 h of perfusion; the total amounts released during this time were 9, 5 and 32 pmol of LTC4, LTD4 and LTE4 respectively. We have used two different methods to prevent the action of the effluent leukotrienes on the heart. Firstly, we have blocked the leukotriene receptors in the heart, with FPL 55712 (3.8 microM), during perfusion with effluent and, secondly, we have perfused with coronary effluent which was collected in the presence of a leukotriene synthesis inhibitor, AA861 (1 microM). The addition of FPL 55712 to the effluent decreased the normally observed vasoconstriction such that after 30 min the coronary flow rate (CFR) was 114 +/- 3% (n = 6) compared with 66 +/- 1% (n = 7) with effluent alone (P less than 0.005). Effluent collected in the presence of AA861 also caused a decrease in the normally observed vasoconstriction such that by 30 min the CFR was still 88 +/- 2% (n = 6, P less than 0.005 compared to controls). We have confirmed the proposed involvement of leukotrienes in the effluent-induced vasoconstriction by investigating the effect of a mixture of the synthetic leukotrienes C4, D4 and E4, when each of them was present at the same concentration as measured in the coronary effluent; the vasoconstriction observed was superimposable upon that seen with effluent. This vasoactive effect of the leukotriene mixture was not secondary to a change in contractility, since this only decreased to 97 +/- 5% (n = 9) during the 30 min of the leukotriene infusion. Finally, we have studied the effects of the same two leukotriene blockers in normal, buffer-perfused hearts after an initial perfusion of either 30 or 120 min. Application of either AA861 or FPL 55712 resulted in a dramatic vasodilatation (25 to 45% increase), a larger effect always being observed after the shorter initial period of perfusion. Our conclusions are two-fold. Firstly, isolated, buffer-perfused rat hearts synthesize leukotrienes C4, D4 and E4 in considerable amounts and release them into the coronary effluent and secondly, the coronary flow rates of isolated, buffer-perfused rat hearts are partly controlled by the action of internally produced leukotrienes.

Animals↗
PubMed1989

Endothelin-1 is a potent constrictor in conductive and resistive coronary arteries.

The action of endothelin-1 (ET-1) in canine and porcine coronary artery ring preparations and perfused canine and porcine myocardium was examined in vitro to determine the site of action of ET-1 in the coronary vasculature. ET-1 had a vasoconstrictor effect that was more potent in smaller diameter ring preparations. The EC50s for both canine and porcine ring preparations decreased with a decrease in vessel diameter and the EC50 of ET-1 in the perfused myocardium was three to four times lower than in the smallest ring preparation. The results suggest that ET-1 may cause cardiac ischemia by constriction of resistive vessels rather than by epicardial coronary artery spasm.

Animals↗
PubMed1988

Endothelin induces potent microvascular constriction.

Endothelin is a recently discovered peptide produced by endothelial cells. It has been shown to have potent constrictor effects on major arteries in vitro and to raise rat blood pressure in vivo. The present experiments show that endothelin has a potent constrictor action on the microvasculature. Blood flow changes were measured by a xenon clearance technique in rabbit skin. Endothelin, when injected intradermally into rabbit skin, decreased local blood flow in a dose-dependent manner. Endothelin reduced basal skin blood flow and reversed the increased blood flow induced by a vasodilator. These results show that endothelin, administered extravascularly, has potent vasoconstrictor activity. This adds further support to the suggestion that endothelin may have an important role in the physiological control of blood flow and pressure.

Animals↗
PubMed1988

Leukotriene release by human fetal membranes, placenta and decidua in relation to parturition.

Complete placentas and membranes were obtained from women after uncomplicated singleton pregnancies. Six were collected after labour at term, six after preterm labour and six after elective Caesarean section at term. Leukotriene C4 (LTC4), leukotriene D4 (LTD4) and leukotriene E4 (LTE4) release was examined using a short-term incubation technique. Release by amnion was significantly higher than that by the other tissues for the three modes of delivery. Comparison of LTC4, LTD4 and LTE4 release by individual tissues with regard to the type of delivery showed no significant difference.

Cesarean Section↗
PubMed1988

Bradykinin- and chemotactic peptide fMLP-stimulated leukotriene biosynthesis in rat lungs and its inhibition by vasoactive intestinal peptide.

The release/biosynthesis of peptidoleukotrienes (pLT) from rat lung tissue was stimulated with either bradykinin (Bk) or the chemotactic peptide formyl-methionyl-leucinyl-phenylalanine (fMLP). Bk- and fMLP-induced stimulation of pLT levels was dose-related for leukotriene D4 (LTD4), E4 (LTE4) and total pLTs and was maximal when a 10 microM concentration of either peptide was used. This stimulation was partially counteracted by vasoactive intestinal peptide (VIP), in agreement with the previously reported VIP inhibition of platelet activating factor- and IgG-stimulated pLT biosynthesis.

Animals↗