Effects of dietary flaxseed on vascular contractile function and atherosclerosis during prolonged hypercholesterolemia in rabbits

Dietary flaxseed has significant anti-atherogenic effects. However, the limits of this action and its effects on vascular contractile function are not known. We evaluated the effects of flaxseed supplementation on atherosclerosis and vascular function under prolonged hypercholesterolemic conditions in New Zealand White rabbits assigned to one of four groups for 6, 8, or 16 wk of feeding: regular diet (RG), 10% flaxseed-supplemented diet (FX), 0.5% cholesterol-supplemented diet (CH), and 0.5% cholesterol- and 10% flaxseed-supplemented diet (CF). Cholesterol feeding resulted in elevated plasma cholesterol levels and the development of atherosclerosis. The CF group had significantly less atherosclerotic lesions in the aorta and carotid arteries after 6 and 8 wk than the CH animals. However, the anti-atherogenic effect of flaxseed supplementation was completely attenuated by 16 wk. Maximal tension induced in aortic rings either by KCl or norepinephrine was not impaired by dietary cholesterol until 16 wk. This functional impairment was not prevented by including flaxseed in the high-cholesterol diet. Aortic rings from the cholesterol-fed rabbits exhibited an impaired relaxation response to acetylcholine at all time points examined. Including flaxseed in the high-cholesterol diet completely normalized the relaxation response at 6 and 8 wk and partially restored it at 16 wk. No significant changes in the relaxation response induced by sodium nitroprusside were observed in any of the groups. In summary, dietary flaxseed is a valuable strategy to limit cholesterol-induced atherogenesis as well as abnormalities in endothelial-dependent vasorelaxation. However, these beneficial effects were attenuated during prolonged hypercholesterolemic conditions.

Adrenergic influences on uterine smooth muscle

1. The mechanism of β adrenergic inhibition of pregnant rat myometrium was investigated. 2. Isoproterenol (4 x 10 -7 mol/l) caused membrane hyperpolarization of about 12 mV . The magnitude of this hyperpolarization was unaffected by K-free and Cl-free (isethionate substitution) solutions, and was reduced by about 50 % in the presence of ouabain (10 -3 mol/1) and at 10 °C. Hyperpolarization was calcium -dependent, was partially reduced by 12.5 mmol/1 [Ca 2+ ]0 and was abolished when 2.0 mmol/1 La was added to the bathing solution. 3. Isoproterenol (4 x 10 -7 mol/1) increased tissue cyclic AMP levels with a time course paralleling that of the relaxation both at 37 and at 10 °C. Papaverine (10 -4 mol/1) also showed similar actions. 4. Tissue calcium content as measured by the lanthanum technique increased during a K induced contracture and decreased when isoproterenol (4 x 10 -7 mol/1), papaverine (10 -4 mol/1), or dibutyryl cyclic AMP (10 -3 mol/1) relaxed the K contracture. 5. Another relaxant, D-600, a methoxy derivative of verapamil, (10-5 mol/1) had no effect on membrane polarization, tissue cyclic AMP or tissue calcium content. 6. It is concluded that there is an active component to the β adrenergic hyperpolarization of the rat myometium, although an electrogenic sodium pump is not likely to be involved. Rather an electrogenic calcium pump, possibly activated by cyclic AMP, is consistent with the data obtained. Moreover, a mechanism in which cyclic AMP stimulates calcium extrusion may underlie the adrenergically mediated relaxation in the myometrium .

Effect of tetraethylammonium on tonic airway smooth muscle: initiation of phasic electrical activity

We have previously shown that in the presence of tetraethylammonium (TEA, 6.7-67 mM) phasic mechanical activity and a myogenic response (MR) to quick stretch are produced in normally multi-unit tracheal smooth muscle. The present studies were designed to investigate the electrophysiological basis for these changes in the mechanical properties of the muscle. Intracellular recordings showed that in the presence of TEA the membrane was partially depolarized and trains of small (8-20 mV), decrementally conducted action potentials were produced spontaneously at a frequency of 15-20/min. Action potentials could also be stimulated by external electrodes, and the conduction velocity over short distances was 0.84 plus or minus 0.2 cm/s. Membrane conductance and rectification, as measured by the magnitude of electrotonic potentials in response to external stimulation, were reduced in the presence of TEA. The length constant was increased from 1.6 plus or minus 0.1 to 2.8 plus or minus 0.2 mm. These results are consistent with the notion that TEA produces phasic membrane electrical activity by reducing P-K.

Neostriatal administration of somatostatin:differential effect of small and large doses on behavior and motor control

The administration of small doses of somatostatin (SRIF) (0.01 and 0.1 microgram) into the neostriatal complex of unrestrained, freely moving rats induced general behavioral excitation associated with a variety of stereotyped movements, tremors, and a reduction of rapid eye movements (REM) and deep slow wave sleep (SWS). In contrast, the higher doses of SRIF (1.0 and 10.0 microgram) caused movements to be uncoordinated and frequently induced more severe difficulties in motor control such as contralateral hemiplegia-in-extension which restricted or completely prevented the expression of normal behavioral patterns. As a result, the animals appeared drowsy and inhibited. Analysis of the sleep-waking cycle revealed prolonged periods of a shallow SWS while REM sleep and deep SWS were markedly reduced; electroencephalogram recordings revealed periods of dissociation from behavior. The administration of endocrinologically inactive as well as the active analogues of SRIF failed to induce effects comparable with those observed after the administration of the same dose of the native hormone (10.0 microgram).

Evidence that tamoxifen is a histamine antagonist

Recently we reported that both the triphenylethylene antiestrogen tamoxifen, and the novel compound N,N-diethyl-2-[(4 phenylmethyl)-phenoxy]-ethanamine. HCl (DPPE), which is selective for the antiestrogen binding site, may be histamine antagonists and have suggested that the antiestrogen binding site may be a growth-promoting histamine receptor different from H1 and H2 (?H3). We now show that along with established H1-antagonists, tamoxifen and DPPE specifically block the histamine-induced (H1) contraction of canine tracheal smooth muscle in the order: pyrilamine = hydroxyzine greater than tamoxifen = 4-hydroxytamoxifen greater than DPPE. The H1-antagonist hydroxyzine, which competes about equally with DPPE for the antiestrogen binding site, is up to 10(3) times stronger than DPPE in blocking histamine-induced muscle contraction. This shows that H1 antagonism is distinct from binding to the antiestrogen binding site and suggests that if the latter is a histamine receptor, it is not H1; presumably tamoxifen and DPPE compete for this novel site in addition to, and with greater affinity than, H1.

Glucose antimetabolites and hunger (theoretical article)

A decrease in the cellular utilization of glucose produced by several glucose antimetabolites and especially by 2 deoxy-D-glucose considerably stimulates food intake. An analysis of this phenomenon is presented in terms of the available experimental evidence. Experiments in which glucose antimetabolites have been administered so as to influence selectively the central and peripheral glucosensitive loci suggest a possible mechanism for the action of the substances. The mechanisms by which glucose antimetabolites and exogenous insulin induce cellular glucoprivation and the subsequent changes in food intake are compared and discussed.

Induction of a myogenic response in tonic airway smooth muscle by tetraethylammonium

In multi-unit tracheal smooth muscle (TSM), quick stretches applied at a velocity of 5 times the measured maximum velocity of isotonic shortening of the muscle, of a magnitude 3 times the measured extension of the series-elastic component when the muscle contracts maximally, and at optimal muscle length (L-o) were unable to elicit any myogenic response (MR). Experimental conditions such as hypoxia (P-O2 smaller than 60 mmHg) and acidosis (pH equals 6.8) or the presence of Ba2+ (2 mM), acetylcholine (10-6 M), or high (K+)-o (59 mM) were also unable to elicit the MR. However, tetraethylammonium chloride (TEA, 0.4-67 mM) produces 1) spontaneous phasic contractions and 2) a MR to quick stretch. The ionic basis for these changes was then investigated by studying the Ca and Mg dependence of the response to TEA. The dose-response relationship to TEA was shifted to the left by decreasing external Mg2+ from 2.5 to 0.5 mM. The ability of TSM to produce a MR was absolutely dependent on external Ca, but the threshold concentration required shifted from 2.5 times 10-5 M at normal external Mg (2.5 mM) to 5 times 10-4 M at the reduced external Mg (0.5 mM). The effects of TEA on spontaneity and the MR were abolished by D-600. These results suggest that 1) TEA functionally converts multiunit smooth muscle into a single unit one and leads to the development of a MR and 2) the MR results from a depolarization-activated mobilization of Ca and is inhibited by ionic conditions known to increase membrane permeability.

Apparent finger systolic pressures during cooling in patients with Raynaud's syndrome

Despite considerable research, the mechanisms responsible for the vasospasm associated with Raynaud's syndrome are not well understood and there is no reliable diagnostic test. In the present studies, measurements of systolic pressure in locally cooled fingers were used to address these issues. We found that local cooling produced a marked decrease or loss of the apparent finger systolic pressure in patients with Raynaud's syndrome in whom a standardized vasoconstriction had been induced by body cooling. Abnormal responses were encountered in 109 of 125 patients with secondary Raynaud's syndrome, in 21 of 37 patients with primary Raynaud's disease or the syndrome of uncertain cause, and in two of 63 subjects without symptoms of Raynaud's. These data suggest a high accuracy of the test in patients with secondary Raynaud's syndrome and lower accuracy in those with disease of primary or uncertain cause. We studied responses of systolic pressures to alterations in body and local temperatures in fingers with and without low pressures secondary to proximal arterial obstruction. Our data show that although local cooling has a small independent effect that increases vascular tone: (1) sympathetic vasoconstriction induced by body cooling is necessary to produce vasospasm and often produces it without local cooling, (2) high local temperature (30 degrees C) protects from vasospasm, and (3) low finger blood pressure predisposes to it. Delayed opening of the vessels observed after sudden deflation of blood pressure cuffs suggests that abnormal responses of finger systolic pressure to cold represent combined effects of high vascular tone, delayed opening, and local blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of endothelium-dependent vascular relaxation by lysophosphatidylcholine: impact of lysophosphatidylcholine on mechanisms involving endothelium-derived nitric oxide and endothelium derived hyperpolarizing factor

Hyperlipidemia has been associated with an increase in the incidence of atherosclerosis. The oxidation of low density lipoprotein (LDL) plays an important role in the initiation and progression of atherosclerosis, one of its effects being the inhibition of endothelium dependent relaxation (EDR). The elevated level of lysophosphatidylcholine (LPC) in oxidatively modified LDL has been shown to be a biochemical factor responsible for the impairment of EDR in vascular ring preparations. Several endothelium-derived modulators are thought to control vascular responsiveness. The present work examined whether acetylcholine (ACh)-induced EDR in rat aorta (pre-contracted with phenylephrine, PE) involved both endothelium-derived nitric oxide (EDNO) and endothelium-dependent hyperpolarizing factor (EDHF) and whether LPC inhibited either of these selectively. Indomethacin (10(-5) M), had no significant effect on EDR, indicating that products of cyclooxygenase, including prostacyclin, are not involved. Treatment with either N(W)-nitro-L-arginine methyl ester (L-NAME, 6.8 microM) to inhibit the production of EDNO or with elevated K+ (15 mM), to block the hyperpolarizing effect of EDHF impaired EDR considerably (each of these shifting the inhibitory dose-response relationship to ACh by almost one log unit); in muscles treated with both of these agents EDR was completely inhibited. In each of L-NAME- and K-treated muscles, the addition of LPC (20 microM) further impaired EDR. LPC did not independently raise the tone of resting- or PE-contracted aorta. We conclude that the inhibition of EDR of rat aorta by LPC involves the actions of both EDNO and EDHF.

Cataract formation is prevented by administration of verapamil to diabetic rats

The purpose of the present study was to examine the effects on cataractogenesis of daily sc administration of the Ca2+ antagonist drug verapamil to diabetic rats. Streptozotocin-induced diabetic rats were given verapamil half-way through the 8-week experimental period or during the full 8 weeks of diabetes. Verapamil administration had no effect on the high blood glucose values, low circulating insulin levels, or elevated triglyceride and cholesterol concentrations in the diabetic rats. Untreated diabetic rats had a 90% incidence of cataracts. Four weeks of verapamil administration reduced this incidence to 41%, and a full 8 weeks of drug treatment further lowered the incidence to 20%. Diltiazem, another Ca2+ antagonist, lowered the incidence of cataracts in the diabetic rats to a similar extent. Verapamil administration to the diabetic animals also partially protected against the presence of retinal microangiopathy in the diabetic animals. Lenticular hydration and lipid accumulation were only indirectly related to cataractogenesis in the diabetic rats and its protection by verapamil treatment. Lenticular electrolyte imbalance, particularly Ca2+, in the diabetic animals was closely correlated with cataract formation, and verapamil significantly reduced the alterations in these ion concentrations. The present results demonstrate the efficacy of verapamil as a protective agent against cataractogenesis and some retinal damage in diabetic animals. Most importantly, this occurs in the absence of any change in the glycemic status of the diabetic animals. The findings strongly support a role for lenticular Ca2+ imbalance in cataract development in diabetes and provide initial evidence to suggest its clinical use in the diabetic population at risk for blindness.

Effects of atorvastatin treatment on the oxidatively modified low density lipoprotein in hyperlipidemic patients

Atorvastatin is an established HMG-CoA reductase inhibitor which effectively reduces the plasma low density lipoprotein (LDL)-cholesterol level in hyperlipidemic patients. The present study was designed to investigate whether atorvastatin treatment can modify the biochemical content of oxidized LDL in hyperlipidemic patients and the ability of oxidized LDL to impair the endothelium-dependent relaxation of blood vessels. With atorvastatin (10 mg/day) treatment for 4 weeks in 19 type IIa hyperlipidemic patients, total cholesterol level was lowered by 23%, LDL-cholesterol was lowered by 32% and triacylglycerol was lowered by 19% as compared with dietary therapy alone. High density lipoprotein levels increased by approximately 9%. The ability of oxidized LDL from hyperlipidemic patients after atorvastatin treatment to impair the endothelium-dependent relaxation was significantly reduced as compared with dietary intervention alone. Analysis of the biochemical contents of oxidized LDL from this group revealed that there was an 11% reduction in lysophosphatidylcholine (LPC) as compared with the group that received only dietary counseling. A decrease in the C16:0 moiety with a corresponding increase in the C18:0 moiety of LPC in the oxidized LDL was also observed in the atorvastatin treated group. We propose that the observed reduction and the change in composition of acyl groups in LPC in the oxidized LDL of the atorvastatin-treated group results from a combination of the continued dietary treatment as well as drug therapy. In view of an observation that both C16:0 and C18:0 LPC species are equally potent in the impairment of endothelium-dependent relaxation of the aortic rings, we feel that the reduced level of LPC in the oxidized LDL produced by atorvastatin treatment is partially responsible for the improvement in endothelium control of vascular tone.

The effect of fenofibrate treatment on endothelium-dependent relaxation induced by oxidative modified low density lipoprotein from hyperlipidemic patients

The objective of the research project was to investigate whether fenofibrate treatment may alter the biochemical content of the oxidized LDL and consequently its ability to impair the endothelium-dependent relaxation in hyperlipidemic patients. We hypothesized that fenofibrate treatment of hyperlipidemic patients may attenuate the ability of their oxidized LDL to impair the endothelium-dependent relaxation of the blood vessels as a consequence of fenofibrate-induced changes to the content and composition of lysoPC in the LDL molecule. Hyperlipidemic patients (Type IIb and Type IV) were recruited from the Lipid Clinic, HSC, Winnipeg, Canada, for this study. A blood sample was taken immediately after the recruitment, a second sample was taken after 6 weeks of dietary treatment, and a third sample was taken after 8 weeks of fenofibrate treatment. LDL was isolated from the plasma and oxidized by copper sulfate. Fenofibrate was shown to be highly effect in the reduction of total cholesterol, LDL cholesterol and triglycerides in these patients. Fenofibrate treatment also caused the attenuation of impairment of endothelium-dependent relaxation by the oxidized LDL from these patients. A slight reduction of lysophosphatidylcholine level was also found in the oxidized LDL of the fenofibrate treated patients, relative to LDL isolated after dietary treatment. In addition there were no changes in the fatty acid levels of the lysophosphatidylcholine isolated from LDL. Taken together, our results suggest that while the reduced lysophosphatidylcholine levels may contribute to the attenuated impairment of the endothelium-dependent relaxation of the aortic ring, other unidentified factors impacted by fenofibrate are likely to contribute to the attenuated effects.

Effect of ionic environment on oxygen uptake and lactate production of myometrium

The present studies were designed to measure the metabolic cost, in terms of oxygen consumption (QO2) and lactate production, of membrane ion transport, and activation of the contractile apparatus of rat myometrium. The normal QO2 of 16.98 +/- 0.84 mumol/g wet tissue per h was reduced to 15.42 +/- 0.66 in the presence of high-K (127 mM) solution. This was further reduced to 14.05 +/- 0.77 and 13.53 +/- 0.76 by the addition of D-600 (10(-5) M), which inhibits Ca influx or in the presence of Ca-deficient high-K solutions, respectively. Ouabain (10(-3) M) reduced QO2 by an amount similar to that produced by high K. Addition of K+ to Na-rich preparations produced an immediate ouabain-sensitive increase of QO2 whose rate was a linear function of [K+]o up to 30 mM in Ca-deficient solution. In all of the above conditions, changes in lactate release paralleled those in QO2. Isoproterenol (10(-6) M), which causes mechanical inhibition of myometrium, had no effect on the QO2 of muscles in normal solution but reduced the QO2 of muscles in Ca-deficient solution. Lactate release was increased by isoproterenol in both normal and Ca-deficient solutions. These results show that the Na pump is an important site of energy utilization in myometrium. Components which can be interpreted in terms of energy utilization for Ca pumping and the contractile apparatus were also demonstrated.

Intracellular pH in hypoxic smooth muscle

Hypoxia impairs contractility in canine tracheal smooth muscle (TSM). This is attributed to intracellular lactacidosis. The present studies were undertaken to confirm this. Lactate was found to be significantly increased in hypoxic TSM (65.36 +/- 7.37 mg/100 g wet tissue), compared to normoxic (29.83 +/- 5.05). Intracellular pH (pHi) was, however, significantly increased in hypoxic active TSM to 7.71 +/- 0.05 as compared to 7.30 +/- 0.03 in normoxic active muscle. pHi of resting normoxic muscle (7.20 +/- 0.04) was statistically not different from that of resting hypoxic muscle. The pHi's of resting normoxic and active hypoxic muscles were significantly different. These results show that under in vitro, hypoxic conditions: 1) an increase in glycolysis in TSM is indicated by the increased lactate production, 2) there is a surprising, concomitant rise in pHi rather than a decrease as previously expected, and 3) it is mechanical activity of the muscle which leads to this paradoxical result, inasmuch as pHi is unaltered in the resting hypoxic muscle.

On the mechanism of the losartan-mediated inhibition of phosphatidylcholine biosynthesis in H9c2 cells

Phosphatidylcholine is the major phospholipid in mammalian tissues and the biosynthesis of phosphatidylcholine in H9c2 cells was previously shown to be stimulated by angiotensin II. In this study, we used the potent AT1 receptor antagonist, losartan, to determine if the angiotensin II-mediated stimulation of phosphatidylcholine biosynthesis was mediated by AT1 receptors. H9c2 cells were incubated with angiotensin II in the absence or presence of various concentrations of losartan. The cells were then incubated with [methyl-3H]choline for an additional 60 min and the radioactivity incorporated into phosphatidylcholine and its choline-containing metabolites determined. Losartan at concentrations which block AT1 receptors did not effect phosphatidylcholine biosynthesis mediated by angiotensin II. In contrast, higher concentrations of losartan inhibited radioactivity incorporated into phosphatidylcholine and its metabolites and this was due to a losartan-mediated reduction in choline uptake. Kinetic studies revealed that the losartan-mediated inhibition of choline uptake was competitive. High concentrations of losartan caused a translocation of CTP:phosphocholine cytidylyltransferase from the cytosolic (inactive) to the membrane (active) fraction likely as a compensatory mechanism for the losartan-mediated reduction in new phosphatidylcholine biosynthesis. Incubation of cells with PD123319, a potent AT2-receptor antagonist, did not block the angiotensin II-mediated stimulation of phosphatidylcholine biosynthesis. The results suggest that angiotensin II stimulates phosphatidylcholine biosynthesis independent of AT1- and AT2-receptor activation and losartan inhibits phosphatidylcholine biosynthesis by reducing choline uptake in H9c2 cells.

Protection by benzamil against dysfunction and damage in rat myocardium after calcium depletion and repletion

Perfusion of the rat right ventricular wall muscle for 4 min with a Ca2(+)-free medium followed by perfusion with a Ca2(+)-containing solution resulted in a 42% recovery of developed tension, contracture, and a massive release of creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) from the muscle. High concentrations (1-5 mM) of amiloride partially protected the ventricular wall from Ca2+ paradox-induced dysfunction. The inclusion of benzamil, an amiloride analogue, 2 min before and during the Ca2(+)-free perfusion period prevented contracture development, restored force development, and almost totally eliminated the release of CPK and LDH from the muscle. Contractile function was best protected by 10-50 microM benzamil. The results demonstrate the efficacy of benzamil as a protective agent against Ca2+ paradox-induced myocardial dysfunction and damage. In view of the known capacity of benzamil to block transsarcolemmal Na(+)-Ca2+ exchange, this study supports the involvement of elevated intracellular Na+ and a stimulation of Na(+)-Ca2+ exchange in this model of cardiac pathology.