Dietary L-arginine normalizes endothelin-induced vascular contractions in cholesterol-fed rabbits

Reduced contribution of endothelin to the regulation of systemic and pulmonary vascular tone in severe familial hypercholesterolaemia

Vascular dysfunction has been associated with familial hypercholesterolaemia (FH), a severe form of hyperlipidaemia. We recently demonstrated that swine with FH exhibit reduced exercise-induced systemic, but not pulmonary, vasodilatation involving reduced nitric oxide (NO) bioavailability. Since NO normally limits endothelin (ET) action, we examined the hypothesis that reduced systemic vasodilatation during exercise in FH swine results from increased ET-mediated vasoconstriction. Systemic and pulmonary vascular responses to exercise were examined in chronically instrumented normal and FH swine in the absence and presence of the ETA/B receptor antagonist tezosentan. Intrinsic reactivity to ET was further assessed in skeletal muscle arterioles. FH swine exhibited ∼9-fold elevation in total plasma cholesterol versus normal swine. Similar to our recent findings, systemic, not pulmonary, vasodilatation during exercise was reduced in FH swine. Blockade of ET receptors caused marked systemic vasodilatation at rest and during exercise in normal swine that was significantly reduced in FH swine. The reduced role of ET in FH swine in vivo was not the result of decreased arteriolar ET responsiveness, as responsiveness was increased in isolated arterioles. Smooth muscle ET receptor protein content was unaltered by FH. However, circulating plasma ET levels were reduced in FH swine. ET receptor antagonism caused pulmonary vasodilatation at rest and during exercise in normal, but not FH, swine. Therefore, contrary to our hypothesis, FH swine exhibit a generalised reduction in the role of ET in regulating vascular tone in vivo probably resulting from reduced ET production. This may represent a unique vascular consequence of severe familial hypercholesterolaemia.

Role of arginase in the male and female sexual arousal response

The NO-cGMP pathway plays a key role in the male and female genital sexual arousal response. Nitric oxide synthase (NOS) utilizes L-arginine and oxygen as substrates to produce nitric oxide (NO) and citrulline. Arginase is a metalloenzyme that catalyzes the hydrolysis of L-arginine to produce L-ornithine and urea. It is proposed that arginase competes for L-arginine and reduces NOS activity in genital tissues, thus modulating sexual function. Using 2 transition state analogue inhibitors of arginase, 2(S)-Amino-6-boronohexanoic acid (ABH) and S-(2-boronoethyl)-L-cysteine (BEC), we have characterized arginase activity in penile and vaginal tissue. Neither of these inhibitors has activity against NOS. Thus, ABH and BEC are useful compounds for examining the role of arginase in genital tissue physiology, without directly influencing NOS activity. We present data to suggest that arginase may regulate NO production by competing for endogenous pools of L-arginine. In this fashion, arginase is an indirect regulator of penile and vaginal blood flow and specific arginase inhibitors may improve genital blood flow during sexual arousal. As evidenced by the upregulation of arginase in specific disease states, its distribution in the vagina, and its modulation by sex steroid hormones, this enzyme may also participate in numerous other physiological and pathophysiological processes, such as tissue growth, fibrosis, and immune function.

Nucleoprotamine diet derived from salmon soft roe protects mouse hippocampal neurons from delayed cell death after transient forebrain ischemia

The nutritional benefits of nucleoprotamine (NP), the main component of fish soft roe, have been rarely addressed. In the present study, the preventive effect of oral supplements of nucleoprotamine and its derivatives, DNA and protamine (PT), extracted from salmon soft roe, on survival rate and hippocampal cell death induced by transient brain ischemia, was evaluated in mice. Artificially formulated nucleoprotamine-free (NF) diet with/without nucleoprotamine, DNA or protamine was fed orally. One week after commencement of respective diets, animals were subjected to transient brain ischemia, which was performed by common carotid artery (CCA) occlusion for 25 (severe) or 15 min (mild). After severe ischemia, the survival rate of the NF group was lower than that in the group fed standard diet or NP. Morphological changes in the hippocampal CA1 region were estimated 48 h after mild ischemia. The NP and PT groups significantly decreased the neuronal damage compared with the NF group. The number of cell death in the DNA group, however, was affected similar to that of the NF group. Our data suggests that the nucleoprotamine content in salmon soft roe could be a useful nutritional resource for the prevention of cell damage caused by ischemia such as those occurring with cerebral and/or heart infarction.

Dietary L-arginine restores aspirin-induced endothelial dysfunction in rat aorta

L-Arginine induced elevation of the vascular prostanoid led us to think that the risk of coronary spasm may increase in L-arginine consumers when they are subjected to cyclooxygenase inhibitors and this limits the therapeutic value of aspirin. So the aim was to investigate the interaction of aspirin and dietary L-arginine in male rats. Animals were divided into four groups and fed with normal food. The first group received tap water while the second, third and fourth groups were subjected daily to aspirin (8.6 mg/kg), L-arginine (143 mg/kg) and aspirin + L-arginine combination in their drinking water respectively for 7 days. Vasomotor responses were recorded in the aortic rings suspended for isometric-force recordings. Aspirin treatment significantly reduced the dilation to acetylcholine and sodium nitroprusside. Attenuated phenylephrine contractility was associated with normal acetylcholine response in L-arginine group. Addition of L-arginine to aspirin treatment completely prevented aspirin-induced endothelial dysfunction but defective response to sodium nitroprusside persisted. Dietary L-arginine without affecting maximal dilation to acetylcholine significantly increased the share of dilator prostanoid which appears to resist aspirin. These results demonstrated that dietary L-arginine increases dilator prostaoid in rat aortic rings. Contrary to our expectation, co-administered L-arginine protected aspirin induced endothelial dysfunction and ruled out the limitation of aspirin use in L-arginine consumers.

Improvement of vascular function by chronic administration of a cyclo-oxygenase inhibitor in cholesterol-fed rabbits

1. Atherosclerotic cardio- and cerebrovascular disease is a leading cause of mortality in Western countries. Aspirin-like drugs are widely used to prevent and treat these occlusive cardio- and cerebrovascular diseases. The beneficial effects of these drugs have been largely attributed to inhibition of platelet cyclo-oxygenase activity and thromboxane (TX) A2 production. We investigated the effect of an aspirin-like drug, namely indomethacin, on endothelial function, plaque and platelet aggregation and the formation of vasoactive substances during the development of atherosclerosis in cholesterol-fed rabbits. 2. Rabbits were fed 1% cholesterol (n = 8), 1% cholesterol plus 25 mg/day indomethacin (n = 8) or normal rabbit chow (control group; n = 8) for 12 weeks. Urinary excretion rates of 2,3-dinor-TXB2, 6-keto-prostaglandin (PG) F1alpha, 8-iso-PGF2alpha and nitrate were analysed at the beginning of dietary intervention and at 4 weekly intervals thereafter. At the end of the study period, platelet aggregation, aortic plaque formation and endothelium-dependent and -independent vascular functions of isolated aortic rings ex vivo were assessed. 3. Compared with control, in the cholesterol-fed group, urinary 2,3-dinor-TXB2, 6-keto-PGF1alpha and 8-iso-PGF2alpha excretion and platelet aggregation were significantly increased (P < 0.05), but urinary excretion of nitrate was decreased (P < 0.05). Treatment with indomethacin significantly reduced platelet aggregation, urinary 2,3-dinor-TXB2, 6-keto-PGF1alpha and 8-iso-PGF2alpha excretion (P < 0.05 vs the cholesterol-fed group) and attenuated the reduction in urinary nitrate excretion. 4. Cholesterol feeding progressively increased aortic intimal thickening and impaired endothelium-dependent vasodilator function (P < 0.05 vs control), whereas indomethacin partially prevented aortic plaque formation and restored endothelium-dependent vasodilation (P < 0.05 vs the cholesterol-fed group). 5. The present study demonstrates that indomethacin reduces the progression of atherosclerotic lesions and improves endothelium-mediated vascular responses ex vivo in cholesterol-fed rabbits. The beneficial effects of indomethacin may be due to its ability to prevent the elevation of platelet aggregation, TXA2 (measured as urinary 2,3-dinor-TXB2 excretion) and 8-iso-PGF2alpha formation and to retard the decrease in endogenous nitric oxide synthesis (assessed as urinary excretion of nitrate). Despite indomethacin treatment leading to the suppression of prostacyclin biosynthesis (assessed as urinary 6-keto-PGF1alpha excretion), according to our data, indomethacin appears to preserve endothelial function.

Lipids and endothelium-dependent vasodilation--a review

Studies using both in vitro and in vivo techniques have repeatedly shown that endothelium-dependent vasodilation (EDV) is impaired in different forms of experimental as well as human hypercholesterolemia. Clearly this impaired EDV can be reversed by lowering cholesterol levels by diet or medical therapy. Competitive blocking of L-arginine, changes in nitric oxide synthase activity, increased release of endothelin-1, and inactivation of nitric oxide due to superoxide ions all contribute to the impairment in EDV during dyslipidemia. The oxidation of low density lipoprotein, with its compound lysophosphatidylcholine, plays a critical role in these events. However, data on the role of triglycerides and fat-rich meals regarding EDV are not so consistent as data for cholesterol, although a view that the compositions of individual fatty acids and antioxidants are of major importance is emerging. Thus, this review shows that while impaired EDV is a general feature of hypercholesterolemia, the mechanisms involved and the therapeutic opportunities available still have to be investigated. Furthermore, discrepancies regarding the role of triglycerides and fat content in food may be explained by divergent effects of different fatty acids on the endothelium.

Dietary arginine alters time of symptom onset in Huntington's disease transgenic mice

Recent neuroimaging studies reported complex changes in cerebral blood flow (CBF) in early-staged Huntington's disease (HD) patients. Deckel and co-workers [Deckel and Duffy, Brain Res. (in press); Deckel and Cohen, Prog. Neuro-Psychopharmacol. Biol. Psychiatry 24 (2000) 193; Deckel et al., Neurology 51 (1998) 1576; Deckel et al., J. Nucl. Med. 41 (2000) 773] suggested that these findings might be accounted for, in part, by alterations in cerebral nitric oxide (NO) and its byproduct, peroxynitrite. The current experiment tested this hypothesis by altering NO levels via manipulations of dietary L-arginine (ARG), the dietary precursor of NO, in mice transgenic for HD. Seventy-one mice were assigned at 12 weeks of age to one of three isocaloric diets that varied in their content of ARG. These diets included: (a) 0% ARG, (b) 1.2% ARG (i.e. typical mouse chow), or (c) 5% ARG. The 5% ARG diets in HD mice accelerated the time of onset of body weight loss (P<0.05) and motor impairments (P<0.05), and increased resting CBF in HD relative to control (P<0.05). Conversely, the 0% ARG diet demonstrated no loss of body weight and had no changes in CBF relative to controls. However, the 0% ARG HD group continued to show significant deficits on motor testing (P<0. 05). The 1.2% ARG HD group showed reduced body weight loss, better motor functioning, and fewer changes in CBF compared to the 5% ARG HD group. Immunocytochemistry analysis found greater deposition of nitrotyrosine in the cortex, and vasculature, of HD+ mice, 5% and 1. 2%>0% arginine diets. When collapsed across all conditions, CBF inversely correlated (P<0.05) both with the body weight and motor changes suggesting that changes in CBF are associated with behavioral decline in HD mice. Collectively, these findings indicate that dietary consumption of the NO precursor ARG has a measurable, but complex, effect on symptom progression in HD transgenic mice, and implicates NO in the pathophysiology of HD.

Effects of cholesterol diets on vascular function and atherogenesis in rabbits

Vascular endothelial dysfunction is an important early event in atherogenesis. To evaluate the effects of different levels of cholesterol-containing diets on vascular function and atherogenesis, 17 New Zealand White male rabbits were randomized into four groups: Control with noncholesterol, 10-week 0.5% (0.5C-10) or 1% cholesterol (1C-10), and 14-week 0.5% cholesterol (0.5C-14) feedings. After 10 or 14 weeks, the aortas were harvested for studies of vascular endothelial function and percentage surface lipid lesions. The 0.5% and 1% cholesterol feedings resulted in the same degree of hypercholesterolemia independent of the level and period of cholesterol feeding. There was a decreased trend in vascular endothelial-dependent relaxation to acetylcholine in cholesterol-fed rabbits. Fourteen-week cholesterol feeding induced the least vascular dilation at a concentration of 10-7 M acetylcholine (-38 +/- 3%, -23 +/- 4%, -23 +/- 2%, and -15 +/- 5% in control, 0.5C-10, 1C-10, and 0.5C-14 groups, respectively, P = 0.003). More cumulative exposure of arterial walls to cholesterol induced more surface lipid lesions in the aorta (r = 0.877, P < 0.001). There was a negative relationship between aortic lesions and vasodilation (r = -0.557, P = 0.020 for calcium ionophore; r = -0.463, P = 0.062 for acetylcholine). We conclude that the 0.5% and 1% cholesterol feedings induce similar degrees of hypercholesterolemia. However, aortic lipid lesions and vascular reactivity are dependent on cumulative exposure to cholesterol rather than serum cholesterol level only. Furthermore, decreased vascular endothelial relaxation in cholesterol-fed rabbits was related to lipid plaques in the aorta.

Effects of dietary L-arginine on the reactivity of canine coronary arteries

Experiments were designed to determine the effects of supplemental dietary L-arginine on the endothelial and smooth muscle function of canine coronary arteries. One group of dogs was fed the standard laboratory chow while another group was supplemented with 250 mg/kg per day L-arginine. All dogs had undergone bilateral reversed interposition saphenous vein grafting and received 325 mg/day oral aspirin. After 5 weeks of arginine feeding, left circumflex coronary arteries were removed, cut into rings, and suspended for the measurement of isometric force in organ chambers. Concentration-response curves were obtained to L-arginine, UK-14,304 (alpha2-adrenergic agonist) and A23187 (calcium ionophore) in the absence and presence of N(G)-monomethyl-L-arginine (L-NMMA) and tetraethylammonium (TEA) alone or in combination. Serum concentrations of L-arginine increased by about 20% following 2 weeks of arginine feeding and remained elevated throughout the study. In rings with and without endothelium contracted with prostaglandin F2alpha, L-arginine caused concentration-dependent contractions in rings from control animals but no significant change in tension in rings from arginine-fed animals. Contractions to L-arginine in control animals were reduced by either L-NMMA or TEA. Endothelium-dependent relaxations to the alpha2-adrenergic agonist were decreased with arginine feeding while relaxations to the calcium ionophore and the endothelium-derived factor nitric oxide were similar among groups. Relaxations to UK-14,304 were reduced by L-NMMA in both groups but by TEA only in rings from control animals. These results suggest that dietary supplementation with L-arginine modifies reactivity of endothelium and smooth muscle by at least two mechanisms: one associated with activation of potassium channels and the other with receptor-coupled release of nitric oxide.

The effects of chronic L-arginine treatment on vascular responsiveness of streptozotocin-diabetic rats

In this study, the protective effects of L-arginine treatment in vivo on vascular reactivity of streptozotocin (STZ)-induced 12-week-old diabetic rats were examined. Loss of weight, polydipsia, polyphagia, hyperglycemia, hypoinsulinemia, and elevated levels of plasma cholesterol and triglyceride were observed in diabetic rats. L-arginine treatment (1 mg/mL in drinking water) did not significantly affect these metabolic and biochemical abnormalities. Plasma malondialdehyde (MDA) levels in untreated diabetic rats were also significantly higher than untreated controls. However, L-arginine treatment prevented the increase in MDA level of plasma of diabetic rats. Contractile responses, but not sensitivity to noradrenaline (NA), were significantly increased in diabetic rats compared to controls. Treatment of diabetic rats with L-arginine completely prevented the increase in NA responses. Relaxation response to acetylcholine (ACh), but not to sodium nitroprusside (SNP), in diabetic aorta has been found to be significantly decreased as compared with controls. However, there were no significant differences in pD2 values of acetylcholine in either of the groups. L-arginine treatment increased the ACh responses to the control level. All effects of L-arginine on vascular reactivity were found to be specific for diabetic rats and not controls. These results suggest that functional abnormalities occurred in aorta from diabetic rat might at least in part result from L-arginine deficiency, and the lipid peroxidation-lowering effect of L-arginine may account for its protective effect on vascular reactivity of diabetic rats.