Reproducibility of dorsal hand vein responses to phenylephrine and prostaglandin F2 alpha using the dorsal hand vein compliance method

Genetic variation in the α1A-adrenergic receptor and phenylephrine-mediated venoconstriction

There is large interindividual variability and ethnic differences in phenylephrine-mediated vasoconstriction. We tested the hypothesis that genetic variation in ADRA1A, the α_1A adrenergic receptor gene, contributes to the variability and ethnic differences. We measured local dorsal hand vein responses to increasing doses of phenylephrine in 64 Caucasians and 42 African-Americans and genotyped for 32 ADRA1A SNPs. The ED₅₀ ranged from 11 to 5442 ng/min, and the E_max ranged from 13.5% to 100%. The rs574647 variant was associated with a trend towards lower logED₅₀ in each race and in the combined cohort (P=0.008). Additionally, rs1079078 was associated with a trend to higher logED₅₀ in each race and in the combined cohort (P=0.011). Neither variant accounted for the ethnic differences in response. None of the ADRA1A haplotypes was associated with the outcomes. In conclusion, ADRA1A variants do not contribute substantially to the marked interindividual variability or ethnic differences in phenylephrine-mediated venoconstriction.

Blacks have a greater sensitivity to α1-adrenoceptor-mediated venoconstriction compared with whites

Blacks have increased hemodynamic responses to both physiological and pharmacological adrenergic stimulation compared with whites, and this may contribute to the greater prevalence of hypertension in this ethnic group. A small study suggested enhanced α1-adrenoreceptor-mediated arterial vasoconstriction in the forearm vasculature of blacks compared with whites, but it is unknown whether this reflects a generalized vascular phenomenon. The objective of this study was to examine the hypothesis that there are ethnic differences in venous α1-adrenoreceptor responsiveness. Using a linear variable differential transformer, we measured local dorsal hand vein responses to increasing doses of the selective α1-adrenoreceptor agonist, phenylephrine, in 106 subjects (64 whites and 42 blacks). There was wide interindividual variability in responses to phenylephrine. The dose that produced 50% of maximal constriction (ED50) ranged from 11 to 5442 ng/min, and maximal venoconstriction (Emax) ranged from 13.5% to 100%. Blacks (geometric mean ED50 =172 ng/min; 95% confidence interval, 115-256 ng/min) were more sensitive to phenylephrine than whites (310 ng/min; 95% confidence interval, 222-434 ng/min; unadjusted P=0.026; adjusted P=0.003). Median Emax was slightly higher in blacks (89%; interquartile range, 82% to 98%) compared with whites (85%; interquartile range, 75% to 95%; P=0.07). Taken together with previous findings in arterial vessels, our results suggest a generalized increased sensitivity to α1-adrenoreceptor-mediated vasoconstriction in blacks. Increased vascular α-adrenoreceptor sensitivity could predispose to hypertension, and future studies addressing the contribution of this mechanism to ethnic differences in the prevalence of hypertension will be of interest.

Cardiovascular effects of partial sleep deprivation in healthy volunteers

Sleep deprivation is common in Western societies and is associated with increased cardiovascular morbidity and mortality in epidemiological studies. However, the effects of partial sleep deprivation on the cardiovascular system are poorly understood. In the present study, we evaluated 13 healthy male volunteers (age: 31 ± 2 yr) monitoring sleep diary and wrist actigraphy during their daily routine for 12 nights. The subjects were randomized and crossover to 5 nights of control sleep (>7 h) or 5 nights of partial sleep deprivation (<5 h), interposed by 2 nights of unrestricted sleep. At the end of control and partial sleep deprivation periods, heart rate variability (HRV), blood pressure variability (BPV), serum norepinephrine, and venous endothelial function (dorsal hand vein technique) were measured at rest in a supine position. The subjects slept 8.0 ± 0.5 and 4.5 ± 0.3 h during control and partial sleep deprivation periods, respectively ( P < 0.01). Compared with control, sleep deprivation caused significant increase in sympathetic activity as evidenced by increase in percent low-frequency (50 ± 15 vs. 59 ± 8) and a decrease in percent high-frequency (50 ± 10 vs. 41 ± 8) components of HRV, increase in low-frequency band of BPV, and increase in serum norepinephrine (119 ± 46 vs. 162 ± 58 ng/ml), as well as a reduction in maximum endothelial dependent venodilatation (100 ± 22 vs. 41 ± 20%; P < 0.05 for all comparisons). In conclusion, 5 nights of partial sleep deprivation is sufficient to cause significant increase in sympathetic activity and venous endothelial dysfunction. These results may help to explain the association between short sleep and increased cardiovascular risk in epidemiological studies.

Dorsal hand vein responses to the α₁-adrenoceptor agonist phenylephrine do not predict responses to the α₂-adrenoceptor agonist dexmedetomidine

Significant inter-individual variability exists in responses of human dorsal hand veins to activation of α-adrenoceptors. Simultaneous graded infusions of the α₁- and α₂-adrenoceptor agonists phenylephrine (3.66-8000 ng/min) and dexmedetomidine (0.0128-1000 ng/min) were given into dorsal veins of both hands and responses of 75 subjects were analyzed to assess whether a subject's sensitivity to phenylephrine (ED(50)) predicts his sensitivity to dexmedetomidine. Individual ED(50) estimates of dexmedetomidine and phenylephrine ranged between 0.06-412 and 14.2-7450 ng/min and exhibited only a weak positive relationship (r² =0.074, P=0.018). Finger temperature, body mass index, age and phenylephrine sensitivity together accounted for about 30% of dexmedetomidine ED(50) variation (r² =0.315, P<0.001). The large inter-individual variability observed in the responses of dorsal hand veins to both α₁- and α₂-adrenoceptor agonists is not explained by some common factors; instead, dorsal hand vein responsivity is separately determined for both receptor mechanisms.

Desensitization of vascular response in vivo: contribution of genetic variation in the [alpha]2B-adrenergic receptor subtype

OBJECTIVES

Vascular alpha2B-adrenergic receptors (alpha2B-ARs) mediate vasoconstriction and contribute to peripheral regulation of vascular tone. In vitro, a common 301-303 deletion in the alpha2B-AR gene, ADRA2B, results in loss of alpha2B-AR desensitization. We examined the hypothesis that ADRA2B del301-303 or other common ADRA2B variants alter vascular desensitization in vivo.

METHODS

We measured sensitivity to a highly selective alpha2-AR agonist, dexmedetomidine, (0.01-1000 ng/min) in the dorsal hand vein in 41 healthy individuals. To induce desensitization a dose of dexmedetomidine that resulted in submaximal constriction was infused for 180 min and dorsal hand vein responses measured. Desensitization was defined as the ratio between the area-under-the-effect curve for each individual's response and the hypothetical area-under-the-effect curve assuming that the initial response had been maintained for 180 min (ratio below 1 reflecting desensitization). The relationship between six ADRA2B variants (one promoter, three coding, and two in the 3' untranslated region ) with an allele frequency of more than 5% and desensitization was determined.

RESULTS

Forty-one individuals (22 men, 21 whites, age 18-45 years) were studied. The ADRA2B 301-303 deletion allele (ins/del and del/del, n = 18) was associated with resistance to desensitization [1.01 (interquartile range 0.90-1.06)] as compared with ins/ins homozygous individuals (n = 23) [0.91 (interquartile range 0.73-0.99)], P = 0.026. In addition, the -98 GG, 1182 CC, and 1776 CC genotypes were associated with significantly less desensitization than GC or CC, and CA or AA genotypes, respectively.

CONCLUSION

Common ADRA2B variants contribute to the interindividual variability in vascular desensitization to an alpha2-AR agonist in vivo.

Bradykinin or acetylcholine as vasodilators to test endothelial venous function in healthy subjects

INTRODUCTION

The evaluation of endothelial function has been performed in the arterial bed, but recently evaluation within the venous system has also been explored. Endothelial function studies employ different drugs that act as endothelium-dependent vasodilatory response inductors.

OBJECTIVES

The aim of this study is to compare the endothelium-dependent venous vasodilator response mediated by either acetylcholine or bradykinin in healthy volunteers.

METHODS AND RESULTS

Changes in vein diameter after phenylephrine-induced venoconstriction were measured to compare venodilation induced by acetylcholine or bradykinin (linear variable differential transformer dorsal hand vein technique). We studied 23 healthy volunteers; 31% were male, and the subject had a mean age of 33 +/- 8 years and a mean body mass index of 23 +/- 2 kg/m(2). The maximum endothelium-dependent venodilation was similar for both drugs (p = 0.13), as well as the mean responses for each dose of both drugs (r = 0.96). The maximum responses to acetylcholine and bradykinin also had good agreement.

CONCLUSION

There were no differences between acetylcholine and bradykinin as venodilators in this endothelial venous function investigation.

Reduced venous endothelial responsiveness after oral lipid overload in healthy volunteers

The aim of this study was to investigate endothelial venous function, inflammatory markers, and systemic oxidative stress after an oral lipid overload (OLO). We studied 18 healthy adults (9 men; age, 29.2 +/- 0.9 years; body mass index, 22.3 +/- 0.4 kg/m(2)). Blood samples were collected in the fasting state and 3, 4, and 5 hour after the OLO (1000 kcal, 58% fat) for metabolic variables, oxidative stress, inflammatory markers, adiponectin, and resistin. Changes in vein diameter to phenylephrine, acetylcholine, and sodium nitroprusside (dorsal hand vein technique) were measured before and after the OLO. Oral lipid overload increased triglycerides (61 +/- 6 vs 134 +/- 17 mg/dL, P < .001), insulin (7.2 +/- 0.8 vs 10.7 +/- 1.3 muU/mL, P < .05), and resistin (5.38 +/- 0.5 vs 6.81 +/- 0.7 ng/mL, P < .05) and reduced antioxidant capacity (plasma total antioxidant capacity: 186.7 +/- 56 vs 161.8 +/- 50 U Trolox per microliter plasma, P < .01), vascular reactivity (171.3 +/- 85 vs 894.4 +/- 301 ng/mL, P < .001), and maximum acetylcholine venodilation (105.9% +/- 9% vs 61.0% +/- 7%, P < .05). No changes were observed for sodium nitroprusside. Post-OLO triglycerides were positively correlated with phenylephrine dose (rho = 0.38, P < .05) and resistin (rho = 0.43, P < .01) and negatively correlated with the maximum acetylcholine venodilation (rho = -0.36, P < .05). In conclusion, an OLO impaired venoconstriction responsiveness in healthy subjects, probably because of a reduction in the antioxidant capacity.

Effect of a low-dose oral contraceptive on venous endothelial function in healthy young women: preliminary results

BACKGROUND

A possible increase in the incidence of venous thromboembolic events has been reported among users of third generation oral contraceptives. The objective of this study was to evaluate the effect of a low dose oral contraceptive (15 microg ethinyl estradiol/60 microg gestodene) on the venous endothelial function of healthy young women.

METHODS

Prospective case control study using the dorsal hand vein technique. Venous endothelial function was evaluated at baseline and after 4 months in the oral contraceptive users group (11 women) and in a control group (9 women). After preconstriction of the vein with phenylephrine, dose-response curves for acetylcholine and sodium nitroprusside were constructed.

RESULTS

In the contraceptive users group, a reduction occurred in the maximum venodilation response to acetylcholine and sodium nitroprusside after 4 months of oral contraceptive use, but this difference was not statistically significant (P > 0.05). No significant changes were detected in maximum venodilation responses to acetylcholine and sodium nitroprusside at the 4-month time point in the control group.

CONCLUSION

This study found no significant impairment of endothelium-dependent or independent venodilation in healthy young women following oral contraceptive use. Further studies are necessary using the same methodology in a larger sample over a longer follow-up period.

Comparison of inhibitory effects of irbesartan and atorvastatin treatment on the renin angiotensin system (RAS) in veins: a randomized double-blind crossover trial in healthy subjects

Experimental studies point to an interplay between hypercholesterolemia and hypertension, acting through the renin angiotensin system. In a crossover study design with 8 healthy subjects, the authors tested the hypothesis that statin treatment exerts renin angiotensin system-modulating effects in veins by down-regulation of AT1-receptors, resulting in reduced Angiotensin II (Ang II)-induced venoconstriction and by increasing the pleiotropic Ang II-metabolite Ang-(1-7). Irbesartan was used as positive control. Ang II-induced venoconstriction was 49% +/- 9% before and 64% +/- 10% after 30 days of atorvastatin treatment compared to 50% +/- 8% before and 15% +/- 9% after irbesartan (P = .004). Plasma angiotensin levels significantly increased only after irbesartan treatment (Ang II: 35 +/- 4 vs 329 +/- 101 pg/mL [P = .02]; Ang-(1-7): 10 +/- 3 vs 35 +/- 6 pg/mL [P = .01]) compared to atorvastatin treatment (Ang II: 26 +/- 5 vs 31 +/- 4 pg/mL [P = ns]; Ang-(1-7): 9 +/- 2 vs 11 +/- 3 pg/mL [P = ns]). The data indicate that atorvastatin does not inhibit Ang II-induced venoconstriction in vivo and point toward a supportive role of Ang-(1-7) in contributing to the antihypertensive and beneficial vascular effects of irbesartan.

Menopause, estrogens, and endothelial dysfunction: current concepts

Menopause is defined as the permanent cessation of menses. Cardiovascular disease is the leading cause of death among postmenopausal women in developed countries. The disparity between the incidence of cardiovascular disease among women in pre- and postmenopause has been ascribed to the actions of endogenous estrogen on the cardiovascular system and, particularly, on the vascular endothelium. The endothelium plays an important role in cardiovascular homeostasis, either through the vascular tonus and its regulation, or through coagulation and the inflammatory response. Endothelial dysfunction is implicated in the genesis of atherosclerosis and other chronic disorders, such as diabetes mellitus and hypertension. The pharmacological use of estrogen exerts influence on the circulating levels of markers of vascular tonus, and inflammation, as well as prothrombotic, and fibrinolytic markers, but the impact of these changes on the atherosclerotic disease is still uncertain.

Magnesium-induced vasodilation in the dorsal hand vein

OBJECTIVE

Magnesium affects blood pressure by modulating vascular tone and reactivity. In obstetric patients, magnesium is administered to prevent eclamptic seizures and as a tocolytic to treat preterm labour. Prior to studying vascular sensitivity in women with pre-eclampsia, we sought to determine the effect of magnesium on venous tone in healthy women of childbearing age.

DESIGN

Dose-response study.

SETTING

Columbia-Presbyterian Medical Center, New York.

POPULATION

Ten healthy non-pregnant women (age range 21-47 years).

METHODS

Vascular response to magnesium sulphate (MgSO4) was measured in a dorsal hand vein using the linear variable differential transformer (LVDT) technique. Complete dose-response curves to MgSO4 (0.0000275-0.088 mmol/min) were determined after 50% preconstriction of the vein with phenylephrine.

MAIN OUTCOME MEASURES

The ED50 of MgSO4 (dose resulting in 50% of maximal effect, Emax) was determined. Blood samples from the contralateral upper extremity were obtained to assess total plasma magnesium levels at baseline and at the highest infused dose of magnesium. ED50 results are expressed as geometric mean (95% confidence interval, CI). Emax results and magnesium plasma concentrations are expressed as mean [SD].

RESULTS

The ED50 of MgSO4 was 0.000307 mmol/min (95% CI 0.138, 0.666) and Emax was 102% [20%].

CONCLUSION

Magnesium induces dose-dependent venodilation in healthy women in the absence of systemic haemodynamic effects. The dose resulting in vasodilation using the LVDT/hand vein model is two to three orders of magnitude less than the therapeutic doses of magnesium used for tocolysis or seizure prophylaxis. Studies of the effect of systemically administered therapeutic doses of magnesium on vascular reactivity in pre-eclampsia will be of interest.