Blockade of Vasospastic Attacks by α2-Adrenergic but Not α1-Adrenergic Antagonists in Idiopathic Raynaud’s Disease
Background Idiopathic Raynaud’s disease is characterized by cold-induced digital vasospasms, but its origin has not been established. Previous research has shown that peripheral vascular α2-adrenergic receptors are hypersensitive to local cooling in these patients, but the role of α1-adrenergic receptors is not clear. Moreover, the role of adrenergic receptors in the production of actual vasospastic symptoms has not been investigated.
Methods and Results We studied 23 patients with idiopathic Raynaud’s disease who were screened using conservative criteria. They were randomly assigned to receive brachial artery infusions of an α1-antagonist, an α2-antagonist, or both while vasospastic attacks were induced by cooling in the laboratory. Each patient’s hands were photographed, and the number of attacks in the infused hand was compared with the number in the contralateral hand. The number of fingers (mean±SEM) with attacks in infused hands was yohimbine 0.3±0.3, prazosin 2.3±0.3, and both drugs 0.6±0.2. The difference between prazosin and the other two drug groups was significant (P<.001).
Conclusions These findings demonstrate that activation of α2-adrenergic receptors but not α1-adrenergic receptors is necessary for the production of vasospastic attacks in idiopathic Raynaud’s disease.
Idiopathic Raynaud’s disease is characterized by digital vasospastic attacks that are usually provoked by exposure to cold. Although the prevalence of the disease is not known, estimates range from 4.3% of women in the southern United States1 to 19% in the United Kingdom.2
Two main theories have been postulated to explain the pathophysiology of idiopathic Raynaud’s disease. Raynaud3 hypothesized that excessive sympathetic nervous system activity caused an increased vasoconstrictive response to cold, whereas Lewis4 hypothesized that a “local fault” caused cold hypersensitivity of the digital arteries.
Recent evidence favors the theory of Lewis. It has been shown that the vasospastic attacks of Raynaud’s disease can be provoked despite digital nerve blockade5 and that sympathetic nerve impulse activity in these patients is normal.6 It also has been shown that vasoconstrictive responses to intra-arterial clonidine (an α2-adrenergic agonist) are significantly greater in idiopathic Raynaud’s disease patients than in healthy volunteers.7 8 However, the role of α1-adrenergic receptors in Raynaud’s disease is not clear. Whereas some investigations have found increased vasoconstrictive responses to intra-arterial phenylephrine (an α1-adrenergic agonist) in Raynaud’s disease patients,7 9 others have not.8 Moreover, the role of adrenergic receptors in actual vasospastic attacks has not been studied.
There is considerable evidence that α2-adrenergic receptors are more important than α1-adrenergic receptors in agonist-induced and cold-induced vasoconstriction. Coffman and Cohen10 showed that intra-arterial clonidine was considerably more potent than intra-arterial phenylephrine in reducing finger blood flow and that intra-arterial yohimbine (α2-antagonist) but not prazosin (α1-antagonist) significantly increased finger blood flow in a cold room. These findings were supported by subsequent studies showing that an α2-antagonist but not an α1-antagonist abolished cold-induced vasoconstriction in human finger skin11 and that α2-agonists were more potent than α1-agonists in reducing cutaneous blood flow.12
To more precisely delineate the pathophysiology of idiopathic Raynaud’s disease we sought to determine whether α1, α2, or both adrenergic receptor subtypes are necessary to produce vasospastic attacks. We therefore provoked vasospastic attacks in the laboratory during brachial artery infusions of selective α1-adrenergic and α2-adrenergic antagonists.
Twenty-three patients (17 women, 6 men; ages 25 to 57 years old; mean±SD, 41.0±7.7 years old) meeting the Allen and Brown13 criteria for primary Raynaud’s disease were examined by a rheumatologist. All were negative for antinuclear and anticentromere antibodies (tested using HEp2 substrate) and had normal nailfold capillaries using the method of Maricq et al.14 Average patient weight and height were 69.5±10.5 kg and 167.6±7.6 cm, respectively. The average duration of Raynaud’s disease was 9.2±7.3 years, and patients reported an average of 2.0±1.8 vasospastic attacks per day. None of the patients was taking medication, and all gave written informed consent according to procedures approved by our institutional review board.
Maximum Vasodilation Test
All patients received a maximum vasodilation test to determine the patency of digital blood vessels. We have used this procedure before for the same purpose.5 7 9 Patients wearing cotton hospital scrub suits were supine in a 28°C room. Finger blood flow was measured three times per minute from both index fingers, using venous occlusion plethysmography, and recorded on a polygraph.5 7 9
After 16 minutes, patients were heated ventrally and dorsally with two 91×152-cm circulating water pads maintained at 42°C. The upper extremities were not covered by the pads. After 45 minutes of heating, the peak finger blood flow responses to 2 and 4 minutes of ischemia were measured. Data from these patients were compared with data from 29 healthy volunteers (24 women and 5 men, ages 22 to 66 years old) used in our previous research.9 Data from the two groups were compared using repeated measures ANOVAs.
All infusions were performed on a separate day between 12:00 and 4:30 pm. Patients were seated in a 23°C temperature- and humidity-controlled room (relative humidity 45% to 50%). A slow intravenous drip of 0.9% sterile saline solution was started in one arm. In the opposite arm, a 20-gauge catheter was inserted percutaneously into the brachial artery, with lidocaine as the local anesthetic. The catheter was maintained patent with a 0.75 mL/min infusion of 0.9% sterile saline solution administered using a Harvard 901 pump.
Patients were randomly assigned to receive one of three drug infusions: yohimbine HCl (NIH pharmacy, 70 μg/min, 1.8×10−7 mol/min), prazosin HCl (Pfizer, 6 μg/min, 1.4×10−8 mol/min), or both drugs. The doses of prazosin and yohimbine were determined in the following manner: Intra-arterial phenylephrine at 1 μg/min reduces finger blood flow by ≈50% in human subjects.10 This effect is blocked by 6 μg/min prazosin10 but is not affected by 70 μg/min yohimbine.15 Similarly, intra-arterial clonidine at 0.2 μg/min reduces blood flow by ≈50% in human fingers.10 This vasoconstriction is blocked by 70 μg/min yohimbine but is not affected by 6 μg/min prazosin.10 Binding studies have shown that prazosin (α1-adrenergic receptor antagonist) and yohimbine (α2-adrenergic receptor antagonist) are approximately 104 times more selective than each other at their respective receptor subtypes, depending on the tissue used.16 Thus, the antagonists used in the present study are selective for their respective receptor subtypes and are equipotent in the doses given. All drugs were dissolved in 0.9% sterile saline solution and infused at a rate of 1.0 mL/min with a second Harvard 901 pump.
Eight patients were assigned to receive yohimbine, 8 to receive prazosin, and 7 to receive both drugs. There were no differences among these three groups in age, height, weight, sex, duration of disease, reported symptom frequency, or responses to the maximum vasodilation test.
The drug solution was infused for 10 minutes with the room at 23°C. The patient’s hands were then photographed with a Minolta Maxxum 7000 automatic camera with a ring flash, macrozoom lens, and Kodak Ektachrome slide film (ASA 200). As the drug infusion continued, the room temperature was reduced to 4°C in 10 minutes. The room was specially constructed with its own cooling and heating apparatus to accomplish this rapid temperature change. The patient held a 1000-mL beaker of ice water for 2 minutes, and then placed the beaker on a table for 2 minutes, during which time the patient’s hands were again photographed. Anterior and posterior views of the hands were obtained, with a stopwatch in the field of view. We attempted to capture any discernible color changes. This process was repeated for 25 to 45 minutes, until an apparent vasospastic attack occurred. Then the room was rapidly rewarmed, and the catheters were removed. We have used similar methods previously.5
Determination of Attacks
The slides were processed and numbered by the same photographic laboratory, then viewed and rated independently by two raters experienced in work with Raynaud’s disease. The raters were blinded to the drug used and hand being infused. Each finger in each slide was scored as to whether a color change had occurred. A vasospastic attack was defined as two out of the possible three color changes (pallor, cyanosis, or rubor) in the same finger.5
The number of fingers scored as having an attack was determined by each rater for each patient. The data from the two raters were then averaged. The averaged data were analyzed by two-way (drug by hand) ANOVA with simple effects tests.17 Thus, the number of fingers with an attack in the infused hand was compared with the number in the noninfused (control) hand across the three drug groups.
Data from the maximum vasodilation test are shown in Table 1⇓. Heating and ischemia produced significant vasodilation (P<.001), which did not differ significantly between Raynaud’s patients and healthy volunteers.
Results of the infusions are shown in Table 2⇓. Vasospastic attacks occurred in 21 of 23 (91.3%) patients. The ANOVA showed significant effects for hand (P=.0001) and for the hand by drug interaction (P<.0012). For the group treated with yohimbine, significantly fewer attacks occurred in the infused hand than in the noninfused hand (P<.001). In the group treated with prazosin, there was no significant difference between the two hands (P=.74). For the group treated with both yohimbine and prazosin there were significantly fewer attacks in the infused than the noninfused hand (P<.001). However, there was no additional effect of prazosin compared with that of yohimbine alone.
Complete prevention of attacks in the infused arm occurred in 6 of 8 yohimbine group patients, 0 of 8 prazosin group patients, and 5 of 7 yohimbine plus prazosin patients. There was no significant difference (P>.3) among the three groups in the amount of time the ice beaker was held (mean±SEM, 11.4±0.7 minutes). The 2 yohimbine group patients who had attacks held the beaker for 14 and 13 minutes.
In the present investigation, yohimbine but not prazosin significantly blocked vasospastic attacks associated with idiopathic Raynaud’s disease. These data provide strong evidence that activation of α2-adrenergic receptors but not α1-adrenergic receptors is necessary for production of these symptoms. We previously demonstrated that local cooling augments α2-adrenergic vasoconstriction in fingers of patients with Raynaud’s disease but produces the opposite effect in healthy female volunteers.7 Additionally, there is considerable evidence from animal studies that peripheral vascular α2-adrenergic receptors are thermosensitive.18 19 20 Thus, it is likely that cold-induced sensitization of peripheral vascular α2-adrenergic receptors triggers the vasospastic attacks of idiopathic Raynaud’s disease. Other studies have shown increased numbers of platelet α2-adrenergic receptors in Raynaud’s disease patients, suggesting the possibility of a generalized α2-adrenergic receptor abnormality in this group.21 22 23 However, further research is needed to support this hypothesis.
The present study found that prazosin had no effect in attenuating the vasospastic attacks, demonstrating that α1-adrenergic receptor stimulation is not necessary for symptom production. These data are consistent with previous findings that local cooling did not affect α1-adrenergic vasoconstriction in Raynaud’s disease patients.7 Evidence of increased α1-adrenergic responsiveness in Raynaud’s disease may explain the lower finger blood flows sometimes found at comfortable ambient temperatures in these patients.24 However, α1-adrenergic responses do not appear to be necessary to trigger the vasospastic attacks.
We considered the possibility that the lack of effect of prazosin was due to an insufficient dose. However, previous research using similar methods showed that our dose produced significantly increased finger blood flow in a cold room in primary Raynaud’s patients8 and was sufficient to block the vasoconstrictive effects of intra-arterial phenylephrine (α1-agonist).10 Thus, it is highly likely that an α1-antagonist effect was produced by the dose of prazosin in the present study. Even if we had achieved partial α1-adrenergic blockade, one would have expected prazosin to cause some reduction in the number of attacks, albeit less than that of yohimbine. However, we did not obtain that result.
Each patient served as his or her own control in the present study, since we compared attacks in the infused hand with those in the contralateral hand. Thus, hormonal effects cannot explain our findings. Moreover, because our patients were conservatively classified and showed normal responses to a maximum vasodilation test, it is unlikely that our results are due to vascular wall hypertrophy in some fingers.
In conclusion, the present study demonstrates that α2-adrenergic receptor but not α1-adrenergic receptor activation is necessary to induce vasospastic attacks in idiopathic Raynaud’s disease. Future research should attempt to determine the causes of this α2-adrenergic receptor abnormality and to develop effective therapeutic interventions to ameliorate it.
This work was supported by research grant HL-30604 from the National Heart, Lung, and Blood Institute. We thank Janice Rodriguez for technical assistance; Daniel Colaluca, PharmD, for preparing the drugs; Dena Norton for analyzing the data; Helen Brewster for preparing the manuscript; and Pfizer Inc for donating the prazosin.
- Received February 14, 1995.
- Accepted March 27, 1995.
- Copyright © 1995 by American Heart Association
Simlan A, Holligan S, Brennan P, Maddison P. Prevalence of symptoms of Raynaud’s phenomenon in general practice. Br Med J. 1990;301:590-592.
Raynaud M; Barlow T, trans. New Research on the Nature and Treatment of Local Asphyxia of the Extremities. London, England: New Syndenham Society; 1888.
Lewis T. Experiments relating to the peripheral mechanism involved in spasmodic arrest of circulation in fingers, a variety of Raynaud’s disease. Heart. 1929;15:7-101.
Freedman RR, Mayes MD, Sabharwal SC. Induction of vasospastic attacks despite digital nerve block in Raynaud’s disease and phenomenon. Circulation. 1989;80:859-862.
Fagius J, Blumberg H. Sympathetic outflow to the hand in patients with Raynaud’s phenomenon. N Engl J Med. 1971;285:259-263.
Coffman JD, Cohen RA. α2-Adrenergic and 5-HT2 receptor hypersensitivity in Raynaud’s phenomenon. J Vasc Med Biol. 1990;2:100-106.
Freedman RR, Sabharwal SC, Desai N, Wenig P, Mayes M. Increased α-adrenergic responsiveness in idiopathic Raynaud’s disease. Arthritis Rheum. 1989;33:61-65.
Ekenvall L, Lindblad LE, Norbeck O, Etzell B-M. α-Adrenoceptors and cold-induced vasoconstriction in human finger skin. Am J Physiol: Heart Circ Physiol. 1988;24:H1000-H1003.
Freedman RR, Sabharwal SC, Moten M, Migály P. Local temperature modulates α1- and α2-adrenergic vasoconstriction in men. Am J Physiol. 1992;263:H1197-H1200.
Ruffolo RR, DeMarinis RM, Wise M, Hieble JP. Structure-activity relationships for alpha-2 adrenergic receptor agonists and antagonists. In: Limbird L, ed. The Alpha-2 Adrenergic Receptors. Clifton, NJ: Humana; 1987:115-186.
Winer BJ. Statistical Principles in Experimental Design. New York, NY: McGraw-Hill Publishing Co Inc; 1971.
Flavahan NA, Lindblad LE, Verbeuren TJ, Shepherd JT, Vanhoutte PM. Cooling and α1- and α2-adrenergic responses in cutaneous veins: role of receptor reserve. Am J Physiol. 1985;249(Heart Circ Physiol 18):H950-H955.
Flavahan NA, Vanhoutte PM. Effect of cooling on alpha-1 and alpha-2 adrenergic responses in canine saphenous and femoral veins. J Pharmacol Exp Ther. 1986;238:139-147.
Faber JE. Effect of local tissue cooling on microvascular smooth muscle and postjunctional α2-adrenoceptors. Am J Physiol. 1988;255(Heart Circ Physiol 24):H121-H130.
Coffman JD, Cohen AS. Total and capillary fingertip blood flow in Raynaud’s phenomenon. N Engl J Med. 1971;285:259-263.