The acute effects of nifedipine on calf and forefoot blood flow in patients with peripheral arterial insufficiency

Protective effect of the K+ channel opener KRN4884 on peripheral occlusive arterial disease in rats

1. The effect of the potassium channel opener KRN4884 on the peripheral arterial occlusion model induced by laurate was examined and compared with that of beraprost sodium and nilvadipine. 2. KRN4884 or beraprost sodium prevented macroscopic changes in the paw after the injection of laurate. In contrast, nilvadipine did not improve the lesions. 3. KRN4884 produced a dose-dependent increase in gastrocnemius blood flow in the chronic femoral artery-ligated rats. The effect of KRN4884 on the blood flow was stronger in the hypoxic muscle than in the normal muscle. 4. KRN4884 did not have a direct antiplatelet aggregation activity. 5. These findings suggest that KRN4884 is useful for the therapy of peripheral arterial occlusive disease and that the effect of KRN4884 is associated with an increase in blood flow in ischemic skeletal muscle.

Experimental models of chronic lower extremity arterial occlusive disease: lessons for drug development

Peripheral vascular disease is the result of chronic vascular insufficiency. As the vascular insufficiency of the lower limbs progressively deteriorates, the condition progresses from intermittent claudication (pain upon exercise) to pain at rest and gangrene. In very severe cases amputation of the leg may be necessary. Whilst dieting, cessation of smoking and physical exercise all beneficially affect the progression of the disorder, the available drug therapy is of limited benefit. Very effective pharmacological agents capable of alleviating the symptoms of chronic peripheral vascular disease have not been developed. In order to mimic the vascular insufficiency of intermittent claudication, an animal model was developed in rats. This involves short-term and long-term 6-10 weeks ligation of the femoral artery of the rat. As demonstrated using measurements of hindlimb skeletal muscle, blood flow, pO2, metabolism and function, a model of intermittent claudication was produced. Using this model, the beneficial effects of physical training was demonstrated. Physical training induced an increase in blood flow and a greater capacity for aerobic metabolism in the partially ischaemic skeletal muscle. The effect of vasodilators has also been examined in this model; in contrast to agents such as Ca2+ antagonists, K+ channel openers appear to improve nutritional blood flow and metabolism in the afflicted skeletal muscle. This model can also be utilized to demonstrate the effects of haemorrheological interventions and of agents modulating muscle metabolism. However, additional effort is required to develop models for the evaluation of efficacy of antiatherothrombotic drugs.

Effect of felodipine on regional blood supply and collateral vascular resistance in patients with peripheral arterial occlusive disease

This double-blinded, randomized, placebo-controlled study was designed to investigate the acute effect of felodipine on regional blood supply and collateral vascular resistance in patients with peripheral arterial occlusive disease (PAOD). Thirty men with PAOD were treated with a single dose of 5 mg felodipine or placebo. Systolic blood pressure (SBP), Doppler ankle pressure (DAP), calf blood flow (CBF) by venous occlusion plethysmography and calf transcutaneous oxygen tension (tcpO2) were measured during a cycle ergometry. Felodipine reduced SBP significantly (from 149 to 136 mmHg, p < 0.05), while placebo did not. DAP increased slightly but not significantly in both groups. The pressure gradient between SBP and DAP fell significantly in the felodipine group (60 vs 39 mmHg, p < 0.01) but not in the placebo group (59 vs 56 mmHg). There was a trend for lower velocity in tcpO2 decrease during the stress test and higher velocity of tcpO2 increase during recovery from exercise in the felodipine group although the differences between both groups were not significant. In the felodipine group, CBF increased by 35.6% (p < 0.05) whereas it did not change in the placebo group. In conclusion, while lowering SBP, felodipine increased slightly, or at least maintained, the blood supply to the calves in PAOD patients, which probably results from reducing collateral vascular resistance.

Double-blind comparison of captopril with nifedipine in hypertension complicated by intermittent claudication

In a double-blind, crossover trial 12 patients with hypertension and peripheral arterial disease were randomized to three months' treatment with captopril 25-50 mg twice daily or nifedipine SR 20-40 mg twice daily. While both treatments were equally effective at lowering blood pressure, postexercise calf blood flow availability was greater during treatment with captopril (P less than 0.04). This was not reflected in walking capacity assessed by treadmill exercise. The results suggest that both captopril and nifedipine are appropriate antihypertensive agents in patients with peripheral arterial disease.

Leg ulcers

The treatment of leg ulcers is a common and sometimes difficult problem. They can be costly to treat and are associated with loss of working capacity and sometimes significant morbidity. In the western world, leg ulcers are most frequently caused by venous insufficiency, arterial insufficiency, neuropathy (usually diabetic), or a combination of these factors. The pathogenesis, clinical features, and management of these types of leg ulcers are emphasized in this review.

beta blockade and intermittent claudication: placebo controlled trial of atenolol and nifedipine and their combination

OBJECTIVE

To determine the effects of the beta 1 selective adrenoceptor blocker atenolol, the dihydropyridine calcium antagonist nifedipine, and the combination of atenolol plus nifedipine on objective and subjective measures of walking performance and foot temperature in patients with intermittent claudication.

DESIGN

Randomised controlled double blind four way crossover trial.

SETTING

Royal Hallamshire Hospital, Sheffield.

SUBJECTS

49 patients (40 men) aged 39-70 with chronic stable intermittent claudication.

INTERVENTIONS

Atenolol 50 mg twice daily; slow release nifedipine 20 mg twice daily; atenolol 50 mg plus slow release nifedipine 20 mg twice daily; placebo. Each treatment was given for four weeks with no washout interval between treatments.

MAIN OUTCOME MEASURES

Claudication and walking distances on treadmill; skin temperature of feet as measured by thermistor and probe; blood pressure before and after exercise; subjective assessments of walking difficulty and foot coldness with visual analogue scales.

RESULTS

Atenolol did not significantly alter claudication distance (mean change -6%; 95% confidence interval 1% to -13%), walking distance (-2%; 4% to -8%), or foot temperature. Nifedipine did not alter claudication distance (-4%; 3% to -11%), walking distance (-4%; 3% to -10%), or foot temperature. Atenolol plus nifedipine did not alter claudication distance but significantly reduced walking distance (-9%; -3% to -15% (p less than 0.003)) and skin temperature of the more affected foot (-1.1 degrees C; 0 to -2.2 degrees C (p = 0.05)). These effects on walking distance and foot temperature seemed unrelated to blood pressure changes.

CONCLUSIONS

There was no evidence of adverse or beneficial effects of atenolol or nifedipine, when given singly, on peripheral vascular disease. The combined treatment, however, affected walking ability and foot temperature adversely. This may have been due to beta blockade plus reduced vascular resistance, which might also explain the reported adverse effects of pindolol and labetalol on claudication.

Nifedipine in patients with peripheral vascular disease

The calcium antagonist nifedipine has been studied in a group of patients with intermittent claudication. In a long-term double blind, placebo controlled trial in 27 patients there was no effect on exercise tolerance as measured by pedal ergometry and only a limited improvement in symptom score on double dose nifedipine. Common femoral artery volumetric blood flow (measured by duplex ultrasound) was unaffected. The acute effects on blood flow were also studied, with a mean increase of 23% in common femoral artery blood flow 30 min after sublingual nifedipine. The administration of nifedipine to patients with peripheral vascular disease will not adversely affect claudication symptoms, and may result in an acute improvement in lower limb blood flow. Nifedipine is a suitable antihypertensive in patients who suffer from intermittent claudication.

In vivo and in vitro evidence of an adenosine-mediated mechanism of calcium entry blocker activities

Drugs such as dipyridamole (200 micrograms/kg/min), an adenosine uptake inhibitor, and theophylline (300 micrograms/kg/min), an adenosine receptor antagonist, respectively increased and decreased postischemic hyperemia in normal subjects, as well as in POAD patients. Moreover, dipyridamole pretreatment was able to antagonize the reduction of peak flow induced by nifedipine, and the potentiating effect of flunarizine on postischemic hyperemia was affected significantly by theophylline, thus suggesting a possible interference of calcium entry blocker drugs with the endogenous adenosine system. In a cellular model (polymorphonuclear leukocytes--PMN) the inhibitory effect of calcium entry blockers on stimulated functions (degranulation and free radical production) was highly antagonized by theophylline. Finally, a 1H-NMR spectroscopy study showed a binding interaction between adenosine and flunarizine on the cell membrane. An adenosine-receptor coupling to the calcium entry blocker channels is suggested.

Effects of nifedipine on the hemodynamic response to clamping and declamping of the abdominal aorta in dogs

Clamping and declamping of the infrarenal abdominal aorta may adversely affect cardiovascular function, particularly in the presence of heart disease. This effect may be further altered by drugs used in the treatment of symptomatic coronary artery disease. The effect of nifedipine on the hemodynamic response to aortic clamping and declamping was determined in 12 dogs anesthetized with 50% nitrous oxide and 0.6% end-tidal isoflurane and monitored with aortic, left ventricular (LV), and thermodilution pulmonary artery catheters. Six dogs received a nifedipine bolus of 100 micrograms/kg followed by an infusion of 4 micrograms/kg/min. Six dogs did not receive any nifedipine and served as controls. Before clamping, nifedipine produced immediate decreases in arterial pressure, systemic vascular resistance (SVR), and LV dP/dt, and a modest increase in cardiac output (CO). During aortic clamping, nifedipine-treated dogs demonstrated marked increases in heart rate (HR), dP/dt, and CO while maintaining a low SVR. There were no significant changes upon declamping. The nifedipine-treated animals maintained a high CO and low SVR. Thus, nifedipine greatly altered the hemodynamic responses to aortic clamping and declamping. Awareness of these alterations is important when caring for patients being treated with nifedipine who are undergoing aortic surgery.

The effects of nifedipine and felodipine on cerebral blood flow during anoxic episodes

Cerebral blood flow (CBF) in the rat was monitored by a venous outflow technique with an extracorporeal circulation, which allows for the continuous recording of flow over periods of several hours. Brief periods of anoxia increase the rate of flow. The dihydropyridine calcium antagonists did not affect basal flow rate and depressed the increase in CBF elicited by anoxia. These findings may have significant implications for the therapeutic use of dihydropyridine calcium antagonists in brain ischaemia.