Pharmacological concentrations of ascorbic acid are required for the beneficial effect on endothelial vasomotor function in hypertension.

Increased production of superoxide anion may contribute to impaired bioactivity of endothelium-derived nitric oxide in hypertension. Ascorbic acid is capable of scavenging superoxide anion; however, experimental studies have shown that high physiological concentrations (>1 mmol/L) of ascorbic acid are required to prevent superoxide-mediated vascular dysfunction. To seek kinetic evidence that superoxide anion contributes to endothelial vasomotor dysfunction in human hypertension, we examined the effects of 2.4 or 24 mg/min ascorbic acid intra-arterial infusions on forearm blood flow responses to methacholine or sodium nitroprusside in 30 patients with hypertension and 22 age-matched controls. Endothelium-dependent vasodilation to methacholine was significantly impaired in the hypertensive patients, with a response to the highest dose of methacholine (10 microg/min) of 12.3+/-6.7 compared with 16.1+/-5.8 mL. min(-1). dL tissue(-1) in the controls (P<0.001). The response to sodium nitroprusside was equivalent in the 2 groups. Ascorbic acid at 24 mg/min significantly improved the forearm blood flow response to methacholine in hypertensive patients with a peak response of 16.1+/-7.1 mL. min(-1). dL tissue(-1) (P=0.001). This dose produced a cephalic vein ascorbic acid concentration of 3.2+/-1. 4 mmol/L. In contrast, ascorbic acid at 2.4 mg/min had no effect on the methacholine response. Ascorbic acid at both doses had no effect on the vasodilator response to sodium nitroprusside in hypertensive patients or the methacholine response in the controls. These results agree with the predicted kinetics for superoxide anion-mediated impairment of endothelium-derived nitric oxide action. Thus, superoxide anion may contribute to impaired endothelium-dependent vasodilation in patients with hypertension.

Drug treatment of peripheral vascular disease.

There are a limited number of clinically effective pharmacotherapeutic agents for treatment of peripheral vascular disorders. Pentoxifylline and cilostazol are available for the symptomatic treatment of intermittent claudication. Analogs of carnitine and L-arginine are being evaluated for treatment of the symptoms of intermittent claudication, and prostaglandins and growth factors are being evaluated for critical limb ischemia. Calcium channel blockers remain the treatment of choice for Raynaud's phenomenon. Alternative vasodilators may be used selectively to treat individuals with Raynaud's phenomenon who are intolerant of calcium channel blockers or in whom such therapy has been unsuccessful. Prostaglandins have been evaluated in patients with refractory Raynaud's phenomenon who also have digital ulceration. The mainstay of short-term treatment (and prophylaxis) of deep vein thrombosis (DVT) has been unfractionated heparin, but now the use of low molecular weight heparin (LMWH) has emerged. Newer agents, such as heparinoids and direct thrombin inhibitors, hold promise for the prevention and treatment of DVT. Prolonged treatment with warfarin is still required to prevent recurrent thrombosis, although the duration of treatment has come under debate.

Association of the expression of an SR-cyclophilin with myeloid cell differentiation.

The role of a 150-kD SR-cyclophilin (NK-TR1) in monocyte differentiation was investigated. Using an antipeptide monoclonal antibody, we have detected NK-TR1 in human peripheral blood monocytes and HL-60 cells. Unstimulated monocytes showed a low intracellular level of NK-TR1 protein that increased over 3 days of lipopolysaccharide + interferon-gamma treatment, consistent with the kinetics of monocyte differentiation. Normal HL-60 cells also had a low level of NK-TR1 protein, and exposure to 1.25% dimethyl sulfoxide (DMSO) resulted in a marked transient increase in expression that returned to basal levels before the development of granulocyte differentiation-associated biochemical changes. Phorbol myristate acetate, a promoter of monocytic differentiation in HL-60 cells, also caused a significant increase in NK-TR1 over basal levels. Transfection of a vector expressing NK-TR1 antisense RNA into HL-60 cells suppressed DMSO-mediated growth arrest. In addition, the development of a more mature phenotype, as measured by expression of CD16, and the ability to reduce nitroblue tetrazoleum dye was inhibited in transfectants when compared with controls. These results are consistent with the hypothesis that the NK-TR1 gene product is required for the progression towards a mature differentiated phenotype.

Vasodilator responses in the forearm skin of patients with insulin-dependent diabetes mellitus.

The integrity of endothelium-dependent vasodilation in the skin of patients with insulin-dependent diabetes mellitus (IDDM) is unclear, especially with respect to the role of nitric oxide. To examine this, forearm skin blood flow by laser Doppler flowmetry and total blood flow by venous occlusion plethysmography was measured in response to brachial artery infusions of an endothelium-dependent (methacholine) and -independent (sodium nitroprusside) vasodilator. Peak hyperemic forearm blood flow, following 5 min of arterial occlusion, was also determined. Responses were compared in 11 control subjects and 16 patients with insulin-dependent diabetes mellitus. In ten normal subjects, co-infusion of NG-monomethyl-L-arginine with methacholine produced a significant reduction in total forearm blood flow response to methacholine (p < 0.002), measured by venous occlusion plethysmography, as well as vascular conductance (p < 0.001), confirming that nitric oxide contributes to this response. In contrast, NG-monomethyl-L-arginine had no significant effect on the methacholine-induced increase in forearm skin blood flow measured by laser Doppler flowmetry indicating that factors other than nitric oxide may be involved. Increases in forearm skin blood flow in response to methacholine, sodium nitroprusside and to an ischemic stimulus were not significantly different between the normal subjects and patients with IDDM. Dose-related increases in total forearm blood flow and vascular conductance were not significantly different between control subjects and diabetic patients during infusions of methacholine. The increases in these parameters during infusions of sodium nitroprusside, however, were significantly less in the diabetic group than in the control group (p < 0.05) as was the peak reactive hyperemic blood flow (p < 0.05). Since skin blood flow was not affected, the reduced vasodilator responses to sodium nitroprusside and an ischemic stimulus in the diabetic group are in forearm skeletal muscle. The reduced muscle blood flow does not reflect a decreased vasodilatory capacity, but rather a functional impairment in response to nitric oxide and ischemia since the methacholine dilation was normal. The normal vasodilator responses in the forearm skin, which is predominantly capillary as opposed to arteriovenous anastomatic blood flow, indicate that the response to nitric oxide and an ischemic stimulus in this vascular bed is intact in patients with IDDM. This is, therefore, an unlikely cause of diabetic skin, complications in these areas.

Effects of endothelium-derived nitric oxide on skin and digital blood flow in humans.

The effects of NG-monomethyl-L-arginine (L-NMMA) on total finger and forearm, and dorsal finger and forearm skin, blood flows were studied in the basal state and during reflex sympathetic vasoconstriction in normal subjects. Total flows were measured by venous occlusion plethysmography and skin flows by laser-Doppler flowmetry (LDF). L-NMMA in doses of 2, 4, and 8 microM/min given by constant infusion via a brachial artery catheter significantly decreased finger blood flow, forearm blood flow, and vascular conductances. At 8 microM/min, total finger blood flow decreased 38.4% and forearm blood flow decreased 24.8%. Dorsal finger and forearm skin LDF were also significantly decreased (25 and 37% at 8 microM/min). Body cooling significantly decreased finger blood flow (73.6%), vascular conductance, and finger LDF (59.7%). L-NMMA had no effect on total finger blood flow or dorsal finger LDF during body cooling. Nitric oxide or related compounds contribute to the basal dilator tone of the dorsal finger and forearm skin but not during reflex sympathetic vasoconstriction.

Enhanced cholinergic cutaneous vasodilation in Raynaud's phenomenon.

BACKGROUND: Vasodilator function was determined in patients with Raynaud's phenomenon during intra-arterial infusions of the endothelium-dependent and -independent vasodilators, methacholine and sodium nitroprusside, respectively. Reactive hyperemia, induced by 5 minutes of arterial occlusion with exercise, was also measured. METHODS AND RESULTS: Total blood flow was measured in the fingertip and forearm by venous occlusion plethysmography, and blood flow in the forearm skin was determined with laser Doppler flowmetry. Basal fingertip blood flow was not significantly different between control subjects and patients with Raynaud's phenomenon. Infusions of methacholine had no significant effect on fingertip blood flow in control subjects, whereas patients with Raynaud's phenomenon showed a significant increase in fingertip blood flow. Basal total forearm blood flow was significantly lower in patients with Raynaud's phenomenon than in control subjects. Infusions of methacholine and sodium nitroprusside produced dose-related increases in total forearm blood flow that were of similar magnitudes in the two groups, as were the reactive hyperemic responses. Laser Doppler measurements of forearm skin blood flow, however, showed a significantly greater vasodilator response to methacholine in patients with Raynaud's phenomenon than in control subjects. Infusions of sodium nitroprusside produced a relatively small vasodilator response in the skin of the forearm that was smaller than that to methacholine and not significantly different between the two groups. CONCLUSIONS: In Raynaud's phenomenon, a greater vasodilator response to infusions of methacholine in the fingertip, where changes in blood flow mainly reflect those of skin, and in the skin of the forearm may reflect increased responsiveness of cutaneous blood vessels to stimulation of the endothelium. The mechanism involved is unclear but may result from a general abnormality of blood vessels in the skin, which is related to the pathophysiology of cutaneous vasospasm.

Plasma levels of 5-hydroxytryptamine during sympathetic stimulation and in Raynaud's phenomenon.

1. The involvement of plasma 5-hydroxytryptamine in normal subjects during sympathetic stimulation and in patients with Raynaud's phenomenon was studied. 2. Arterial and venous plasma levels of 5-hydroxytryptamine were measured in normal subjects in a warm room, during reflex sympathetic stimulation by body cooling and during intra-arterial infusions of tyramine. Normal subjects (n = 19) had significantly higher levels of 5-hydroxytryptamine in venous plasma [mean 1.42 (SEM 0.23) ng/ml] than in arterial plasma [0.67 (0.12) ng/ml; P < 0.01]. Body cooling (n = 10) or tyramine infusion (n = 8) did not increase venous levels of 5-hydroxytryptamine despite significant decreases in blood flow and increases in vascular resistance. 3. Venous plasma levels of 5-hydroxytryptamine were also determined in patients with primary Raynaud's phenomenon (n = 12) or secondary Raynaud's phenomenon due to scleroderma (n = 11). Patients with primary or secondary Raynaud's phenomenon did not have significantly higher venous plasma levels of 5-hydroxytryptamine than normal subjects, even during vasospastic attacks (n = 3). 4. It is concluded that either 5-hydroxytryptamine is not involved in sympathetic nerve vasoconstriction or in Raynaud's phenomenon, or 5-hydroxytryptamine released in the microcirculation is largely taken up or metabolized by endothelial cells or platelets.

Chronic inhibition of nitric oxide production augments skin vasoconstriction in the rabbit ear.

The effect of chronic inhibition of nitric oxide (NO) synthesis by NG-nitro-L-arginine methyl ester (L-NAME) on cutaneous ear blood flow (EBF) in the rabbit was examined in vivo with use of laser Doppler flowmetry. Additionally, the efficacy of inhibition of NO by L-NAME was studied ex vivo in isolated preparations of aortic rings from these rabbits. Before surgical implantation of osmotic pumps loaded with L-NAME, resting EBF was not significantly different in rabbits selected for control or L-NAME treatment. Although chronic L-NAME treatment had no significant effect on resting core temperature, resting EBF was reduced significantly in L-NAME-treated rabbits as compared with EBF in control rabbits. Short-term body warming for 10-20 min caused a significant increase in EBF, but not in body temperature, to levels that were not significantly different between groups at 0, 1 and 2 weeks. Prolonged body warming for a further 30-40 min produced a rise in body temperature and a further increase in EBF of 22% to levels that were not significantly different in control and L-NAME-treated groups. Acetylcholine-induced relaxations of aortic rings and levels of cyclic GMP were significantly reduced in L-NAME-treated rabbits as compared with control rabbits, whereas relaxations to sodium nitroprusside were enhanced significantly. These findings demonstrate that the synthesis of NO can be inhibited chronically in the rabbit and are consistent with the concept that NO participates in the control of skin blood flow by counteracting vasoconstrictor tone but not in the vasodilation induced by body warming.

Alpha-adrenergic and serotonergic receptors and forearm venous compliance in normal human subjects.

The effect of alpha-adrenergic and serotonergic receptor agonists and antagonists on forearm venous capacitance and vascular resistance was studied in normal subjects. Venous volumes were significantly decreased by phenylephrine, an alpha 1-adrenoceptor agonist, and norepinephrine, which stimulates both alpha 1- and alpha 2-adrenoceptors, but not by the alpha 2-adrenoceptor agonist clonidine. Vascular resistance was increased significantly by all three agonists. Both the alpha 2-adrenoceptor antagonist yohimbine and the alpha 1-adrenoceptor antagonist prazosin attenuated the venoconstrictor and vasoconstrictor response to norepinephrine, indicating that both adrenoceptors are present. 5-Hydroxytryptamine significantly decreased venous volumes, while vascular resistance was not affected. Ketanserin, a 5-HT2 and alpha 1-adrenoceptor antagonist, attenuated the venous volume responses to 5-hydroxytryptamine and phenylephrine. It is concluded that there are alpha 1- and alpha 2-adrenoceptors and 5-HT2 receptors in the forearm venous system. However, vasoactive doses of clonidine are not venoconstricting. Forearm veins are sensitive to doses of 5-hydroxytryptamine, which do not change vascular resistance compared to alpha-adrenoceptor agonists, which affect both.

Raynaud's phenomenon. An update.

The pathogenesis of primary Raynaud's phenomenon remains an enigma. Most evidence favors a local abnormality in the digital arteries as opposed to an increased activity of the sympathetic nervous system. The local fault may involve the alpha 2-adrenergic receptors, which are most important in reflex sympathetic vasoconstriction. Cooling blood vessels increase the sensitivity of alpha 2-adrenergic receptors, increased levels of alpha 2-adrenergic receptors are present in primary Raynaud's disease, and patients show an increased sensitivity to alpha 2-adrenergic receptor agonists on finger blood flow. Serotonin has also been implicated, but the evidence is not compelling. In secondary Raynaud's phenomenon, vasospastic attacks can often be explained by a low arterial distending pressure, a thickened vessel wall, or absence of beta-adrenergic receptor activity. Diagnosis of primary Raynaud's disease relies on a typical history and normal physical examination, laboratory studies, and nailfold capillaroscopy. Finger systolic blood pressures during local cooling with ischemia may be helpful to document vasospastic attacks but does not distinguish primary from secondary Raynaud's phenomenon. The treatment of Raynaud's phenomenon is usually conservative. Pavlovian conditioning or biofeedback may be beneficial. When drug therapy is necessary, the calcium channel entry blocker nifedipine or sympatholytic agents have been shown to decrease the frequency and duration of vasospastic attacks in about two thirds of patients, although subjective improvement does not usually correlate with objective testing. Direct-acting vasodilators have not been shown to be of definite benefit. New therapies include prostaglandins, captopril, and the serotonergic antagonist ketanserin. Surgical sympathectomy has not been beneficial.

Pathogenesis and treatment of Raynaud's phenomenon.

The pathogenetic theories and treatment of Raynaud's phenomenon are reviewed. In primary Raynaud's disease, most evidence supports a local defect at the digital artery level, with vasoconstriction or vasospasm of the digital arteries inducing the color changes. Normal sympathetic activity, low transmural arterial distending forces, and serotonin may be associated factors in the production of vasospastic attacks. In Raynaud's phenomenon, persistent vasoconstriction, thickened vessel walls, increased blood viscosity, and low digital artery blood pressure distal to obstructions may lead to vasospastic attacks with normal sympathetic nerve stimuli. Since the underlying cause of primary Raynaud's disease is unknown, treatment involves the use of agents to reduce sympathetic nerve activity or to prevent vascular smooth muscle contraction. Most patients will respond to conservative measures, but if they fail nifedipine is the drug of choice and alleviates the syndrome in about two thirds of patients. Reserpine and guanethidine may be as effective, but well-controlled studies have not been performed. The beneficial response to prazosin is moderate and dissipates with time. Side effects with these drugs prevent their use in many patients. Diltiazem and nitroglycerin ointments are of questionable value. Ketanserin, a serotonergic S2-receptor antagonist, which has been shown to decrease the frequency of vasospastic attacks, and parenteral prostacyclin are among the new promising therapies.

Deep venous thrombosis and pulmonary emboli: etiology, medical treatment, and prophylaxis.

Risk factors for venous thrombosis include conditions leading to venous stasis, hypercoagulable states, and trauma to veins. The most important factor is venous stasis. Both extrinsic and intrinsic coagulation pathways are intimately involved in the thrombotic process. In recent years, the importance in thrombus formation of the endothelium, platelet products, the fibrinolytic system, and inhibitors of clotting mechanisms has been discovered. Deficiencies of proteins that normally protect against venous thrombosis have been found. Heparin therapy with subsequent warfarin therapy is still the primary treatment for deep venous thrombosis or pulmonary emboli. Fibrinolytic agents lyse pulmonary emboli but are not as effective in deep venous thrombosis. The incidence of serious bleeding complications has hampered the use of fibrinolytic agents except in emergency situations. Even the newer agents, which act more specifically on thrombi instead of on plasma factors, are associated with a similar incidence of hemorrhagic events. Dextrans are a suitable alternative for treatment of deep venous thrombosis when heparin cannot be used. In the prophylaxis of deep venous thrombosis, minidose heparin (5,000 U every 8 hours subcutaneously) is effective, safe, and convenient in most situations. Heparin-dihydroergotamine, dextran, or warfarin can also be used. Aspirin has been disappointing. In orthopaedic surgery, minidose heparin is not protective; large pulmonary emboli may be prevented by starting warfarin therapy at the time of surgery or by daily dextran infusions. Finally, recent studies have shown that lower doses of warfarin than previously recommended are protective against recurrent venous thrombosis and have a reduced risk of hemorrhagic complications.

International study of ketanserin in Raynaud's phenomenon.

PURPOSE: The effects of ketanserin on primary or secondary Raynaud's phenomenon due to connective tissue disease were studied in a large, international group of patients. PATIENTS AND METHODS: The study population consisted of 222 patients from 10 countries. After a run-in period of one month of placebo therapy, patients were randomly assigned in a double-blind manner to receive ketanserin 40 mg three times daily (n = 113) or placebo (n = 109) for three months. Total finger blood flow was measured in 41 patients in a warm and cool room before and during treatment. Vasospastic episodes were assessed by diaries and global evaluations. RESULTS: A significant reduction of 34% in frequency of episodes occurred with ketanserin, compared to 18% with placebo (p = 0.011). There was a 1% reduction in duration of episodes with ketanserin therapy, compared to a 2% increase with placebo therapy, but this finding was not statistically significant (p = 0.29). No difference was observed in severity of attacks. Global evaluations by investigators (p = 0.03) and patients (p less than 0.01) showed an overall benefit with ketanserin compared to that seen with placebo. Patients with primary or secondary Raynaud's phenomenon responded similarly to treatment. No changes in total finger blood flow were found. CONCLUSION: Ketanserin significantly improves the subjective symptoms of patients with primary or secondary Raynaud's phenomenon and is an appropriate agent to use in this disease when conservative measures fail.

Pathophysiology of obstructive arterial disease.

Intermittent claudication is due to ischemia of working muscles in patients with stenoses or obstructions of large or medium sized arteries. Arteriosclerosis obliterans is by far the most common etiology. As an arterial stenosis develops, the distal blood flow and blood pressure are not affected until a critical diameter occurs. Then, blood flow and blood pressure fall precipitously with further narrowing of the lumen area. The most important factors that influence blood flow and the blood pressure drop across a stenosis are the radius of the stenosis and of the artery, and the velocity of blood flow. The velocity of blood flow varies inversely with the peripheral resistance. A decrease in peripheral resistance which occurs with exercise, vasodilator drugs, or sympathectomy leads to an increased blood flow velocity and an increased pressure drop across a stenosis. Thus, a non-critical stenosis at rest can become critical and limit blood flow during exercise. In arterial occlusions and critical arterial stenoses, the distal perfusion pressure is decreased due to the high resistance of the small collateral vessels but blood flow may be normal at rest. With exercise, the distal perfusion pressure decreases to a lower level due to the fall in peripheral resistance. Then, the external pressure of muscle contraction may close the arterial bed and stop blood flow. The stimulus to collateral blood vessel development is not known but may involve the pressure differential across the involved vascular bed and metabolic products produced during the ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of alpha-adrenoceptor subtypes mediating sympathetic vasoconstriction in human digits.

The effects of intra-arterial administration of alpha-1 and alpha-2 adrenoceptor agonists and antagonists on human digital blood flow were studied before and during reflex sympathetic vasoconstriction in normal subjects. Total finger flow was measured by venous occlusion air plethysmography and capillary flow by the disappearance rate of a radioisotope from a local injection in a fingerpad. Intra-arterial phenylephrine (0.2-1.3 micrograms min-1) and clonidine (0.12-0.48 micrograms min-1) produced dose-related decreases in finger blood flow and increases in vascular resistance. Clonidine was the more potent vasoconstrictor. Prazosin (0.4-3 micrograms min-1) effectively blocked the vasoconstrictor effect of phenylephrine but not clonidine, while yohimbine (30-70 micrograms min-1) blocked the effect of clonidine but not phenylephrine. In a 20 degrees C room, prazosin (0.4-13.2 micrograms min-1) caused no significant changes in finger blood flow (7.7 +/- 2.1 to 11.7 +/- 3.3 ml min-1 100 ml-1) or vascular resistance (30.9 +/- 8.8 to 28.1 +/- 8.7 mmHg ml-1 min-1 100 ml-1). In the 20 degrees C room, yohimbine (30-70 micrograms min-1) produced a significant increase in finger blood flow (7.8 +/- 2.8 to 23.4 +/- 6.8 ml, P less than 0.01) and decrease in vascular resistance (20.5 +/- 5.7 to 6.0 +/- 2.2 units, P less than 0.01). No significant changes occurred in finger capillary flow with prazosin or yohimbine infusions. It is concluded that alpha-1 and alpha-2 adrenoceptors are present in human digital vasculature and that alpha-2 adrenoceptors are more important than alpha-1 adrenoceptors in sympathetic neural vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)