Genetic variation in the alpha1B-adrenergic receptor and vascular response.

The alpha1B (α1B)-adrenergic receptors contribute to vasoconstriction in humans. We tested the hypothesis that variation in the ADRA1B gene contributes to interindividual variability and ethnic differences in adrenergic vasoconstriction. We measured dorsal hand vein responses to increasing doses of phenylephrine in 64 Caucasians and 41 African Americans and genotyped 34 ADRA1B variants. We validated findings in another model of catecholamine-induced vasoconstriction, the increase in mean arterial pressure (ΔMAP) during a cold pressor test (CPT). One ADRA1B variant, rs10070745, present in 14 African-American heterozygotes but not in Caucasians, was associated with a lower phenylephrine ED50 (geometric mean (95% confidence interval), 144 (69-299) ng ml-1) compared with 27 African-American non-carriers (208 (130-334) ng ml-1; P=0.015) and contributed to the ethnic differences in ED50. The same variant was also associated with a greater ΔMAP during CPT (P=0.008). In conclusion, ADRA1B rs10070745 was significantly associated with vasoconstrictor responses after adrenergic stimulation and contributed to the ethnic difference in phenylephrine sensitivity.

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 α1A 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 single nucleotide polymorphisms. The ED50 ranged from 11 to 5442 ng min(-1), and the Emax ranged from 13.5-100%. The rs574647 variant was associated with a trend towards lower logED50 in each race and in the combined cohort (P=0.008). In addition, 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.

A common beta1-adrenergic receptor polymorphism (Arg389Gly) affects blood pressure response to beta-blockade.

BACKGROUND: A common polymorphism of the beta(1)-adrenergic receptor Arg389Gly markedly affects function in vitro, but little is known about its in vivo significance. METHODS AND RESULTS: Resting and exercise hemodynamic responses were measured in subjects homozygous for Arg389 (n = 21) or Gly389 (n = 13) alleles before and 3 hours after administration of a beta-blocker, atenolol. Demographic characteristics and atenolol concentrations were similar in the two genotypic groups. Genotype had a marked effect on resting hemodynamic responses to atenolol, with Arg389-homozygous subjects having a larger decrease in resting systolic blood pressure (8.7 +/- 1.3 mm Hg versus 0.2 +/- 1.7 mm Hg, P < .001) and mean arterial blood pressure (7.2 +/- 1.0 mm Hg versus 2.0 +/- 1.7 mm Hg, P = .009). Attenuation of exercise-induced hemodynamic responses by atenolol was not affected by genotype. CONCLUSIONS: There is reduced sensitivity of Gly389 homozygotes to a beta-adrenergic receptor antagonist, and this polymorphism may be an important determinant of variability in response to beta-blockade.

In-vivo effects of Glu298Asp endothelial nitric oxide synthase polymorphism.

Endothelial nitric oxide synthase catalyses the formation of the vasodilator nitric oxide, a major regulator of vascular tone. The Asp298 polymorphism of the nitric oxide synthase gene is associated with altered function and expression of the enzyme in vitro and myocardial infarction and coronary artery spasm in vivo. We examined the effect of the Glu298Asp polymorphism on: (1) local vascular responses to phenylephrine, acetylcholine, glyceryl trinitrate and prostaglandin E1 in the dorsal hand vein; (2) changes in forearm blood flow during mental stress, a measure of nitric oxide-mediated effect on resistance vessels; (3) excretion of urinary nitrite/nitrate as a measure of total body nitric oxide production; and (4) F2-isoprostane metabolite, a measure of oxidative stress, in healthy Glu298 (n = 12) and Asp298 (n = 13) homozygotes. There were no significant differences in acetylcholine dose responses (P = 0.29) in Glu298 and Asp298 homozygotes. Responses to glyceryl trinitrate, prostaglandin E1 and the alpha-adrenergic agonist phenylephrine did not differ by genotype. Forearm blood flow was similar at rest and increased significantly (from 7.5 ml/min/100 ml to 12.2 ml/min/100 ml; P = 0.003), but similarly (P = 0.2), during mental stress in both genotypes. Asp298 homozygotes excreted significantly less nitrate/nitrite than Glu298 homozygotes (nitrate + nitrite/creatinine ratio 0.05 +/- 0.01 vs. 0.09 +/- 0.01, respectively; P < 0.005). Urinary F2-isoprostane metabolite excretion did not differ (Glu298, 2.04 +/- 0.25 ng/mg creatinine; Asp298, 1.85 +/- 0.37 ng/mg creatinine; P = 0.7). We conclude that in healthy volunteers the Glu298Asp polymorphism affects endogenous nitric oxide production without affecting nitric oxide-mediated vascular responses. This polymorphism may only have clinical significance in the presence of endothelial dysfunction.

The effect of common polymorphisms of the beta2-adrenergic receptor on agonist-mediated vascular desensitization.

BACKGROUND: With continuous exposure to beta2-adrenergic agonists, vascular tissue becomes desensitized to agonist-mediated vasodilatation. We studied the effects of two common polymorphisms of the beta2-adrenergic receptor, one at codon 16 and one at codon 27, on agonist-mediated vasodilatation and desensitization in the vascular bed. METHODS: We studied 26 healthy subjects who were selected to represent three genotypes: 7 were homozygous for the alleles encoding Arg16 and Gln27, 8 were homozygous for the alleles encoding Gly16 and Gln27, and 11 were homozygous for the alleles encoding Gly16 and Glu27. Vascular responses were assessed by measuring changes in the diameter of a dorsal hand vein. A dose-response curve of the effect of the beta2-adrenergic-receptor agonist isoproterenol was constructed (dose range, 4 to 480 ng per minute). Desensitization was then induced by a 2-hour continuous infusion of isoproterenol, and venodilatation was measured 30, 60, 90, and 120 minutes after the start of the infusion. RESULTS: Subjects who were homozygous for Arg16 had almost complete desensitization; venodilatation in response to isoproterenol in this group decreased from a mean (+/-SE) of 44+/-11 percent to 8+/-4 percent (P=0.006). In contrast, subjects who were homozygous for Gly16 did not have significant desensitization, irrespective of the amino acid encoded by codon 27. Subjects who were homozygous for Glu27 had higher maximal venodilatation in response to isoproterenol than those who were homozygous for Gln27 (86+/-13 percent vs. 54+/-8 percent, P=0.03). CONCLUSIONS: The Arg16 polymorphism of the beta2-adrenergic receptor is associated with enhanced agonist-mediated desensitization in the vasculature, and the Glu27 polymorphism is associated with increased agonist-mediated responsiveness. Therefore, polymorphisms of the beta2-adrenergic receptor are potentially important determinants of the vascular response to stress.

The effect of sildenafil on nitric oxide-mediated vasodilation in healthy men.

BACKGROUND: Sildenafil, a treatment for erectile dysfunction, is a specific phosphodiesterase type 5 (PDE 5) inhibitor that enhances nitric oxide (NO)-mediated vasodilation in the corpus cavernosum by inhibiting cyclic guanosine monophosphate breakdown. Since PDE 5 is widely expressed in the vasculature, we examined the hypothesis that sildenafil could enhance NO-mediated vasodilation in other vascular beds and improve endothelial function. METHODS: NO-mediated responses to acetylcholine (endothelium-dependent) and nitroglycerin (endothelium-independent) were measured in healthy men in the dorsal hand vein (n = 13), after the administration of either sildenafil 50 mg or placebo. Flow-mediated dilation of the brachial artery and forearm postischemic reactive hyperemia were measured before and after sildenafil 50 mg, isosorbide dinitrate 5 mg, and placebo in a double-blind, randomized, crossover study (n = 11). RESULTS: In the hand vein, sildenafil administration increased sensitivity to local nitroglycerin. The 50% effective dose decreased approximately 4-fold from 13.5 ng/min (range, 6.9-26.6 ng/min) to 2.7 ng/min (range, 1.1-6.4 ng/min) (P =.025). Sildenafil decreased the maximum venoconstriction induced by phenylephrine from 81% +/- 3% to 74% +/- 3% (P =.025). Sildenafil did not significantly affect the maximal venodilatory response to acetylcholine (35% +/- 7% after placebo versus 32% +/- 8% after sildenafil) (P =.7). In the arterial vasculature, flow-mediated dilation before (2.4% +/- 1%) and after (2.8% +/- 1.4%) sildenafil (P =.8) and postischemic reactive hyperemia area under the curve before (1807 +/- 393 mL. min. s/100 mL) and after (1467 +/- 257 mL. min. s/100 mL) sildenafil were not different (P =.8). Resting heart rate, blood pressure, and resting brachial artery diameter were unchanged after sildenafil administration. Isosorbide dinitrate, an endothelium-independent vasodilator, caused a significant increase in resting brachial artery diameter from 0.53 +/- 0.01 cm to 0.56 +/- 0.02 cm (P =.005), without altering flow-mediated dilation. CONCLUSIONS: In healthy men sildenafil increased sensitivity to nitroglycerin, an exogenous NO donor, approximately 4-fold but did not affect endothelium-dependent, NO-mediated responses in either the hand vein or forearm vasculature. Differential vascular responses to sildenafil may localize its enhancement of endogenous NO-mediated vasodilation to vascular beds such as the corpus cavernosum.

In vivo inhibition of human CYP1A2 activity by oltipraz.

PURPOSE: Oltipraz is currently undergoing clinical evaluation as a cancer chemopreventive agent, especially with respect to aflatoxin-associated hepatocarcinogenesis. The agent's ability to induce phase II xenobiotic enzymes that detoxify the ultimate carcinogen formed in vivo is thought to be an important mechanism by which disease risk may be attenuated. However, an additional mechanism could be a reduction in the activation of environmental procarcinogens by certain cytochrome P450 (CYP) isoforms. This hypothesis was tested with respect to CYP1A2, by using the clearance of caffeine by N-demethylation as a phenotypic trait measurement of the isoform's catalytic activity. METHODS: Subjects received a single oral dose of caffeine (200 mg) on five separate occasions: on the day prior to oltipraz administration (day 0), 2 h after the first (day 1) of eight daily oral doses of oltipraz (125 mg) and 2 h after the last dose (day 8). In addition, CYP1A2 activity was also measured 2 and 14 days (days 10 and 22, respectively) after discontinuation of oltipraz administration. Plasma concentrations of caffeine and its N-demethylated metabolite, paraxanthine, over 24 h after drug administration, were determined by HPLC. RESULTS: A single 125-mg dose of oltipraz markedly reduced CYP1A2 activity by 75 +/- 13% in nine healthy subjects, resulting in a higher caffeine plasma level and prolongation of the in vivo probe's elimination half-life. Daily administration of 125 mg oltipraz for 8 days resulted in further inhibition so that only 19 +/- 13% of the original baseline level of activity was present. However, 2 days after discontinuation of oltipraz treatment, CYP1A2 activity had returned to 66 +/- 33% of its original level and complete recovery was achieved within 14 days of the chemopreventive agent being stopped. CONCLUSIONS: These results demonstrate that oltipraz is a potent, in vivo inhibitor of CYP1A2 in humans and, because this isoform is importantly involved in procarcinogen activation, they also indicate that such inhibition probably contributes to oltipraz's cancer-chemopreventive effect. In addition, the findings also suggest the likelihood of significant drug interactions between oltipraz and drugs whose metabolism is mediated by CYP1A2.

Arg389Gly beta 1-adrenoceptor polymorphism varies in frequency among different ethnic groups but does not alter response in vivo.

There are marked interethnic differences in beta 1-adrenoceptor-mediated responsiveness, with sensitivity decreased in African-Americans and increased in Chinese compared with Caucasians. Therefore, the frequency of a common naturally occurring polymorphism of the human beta 1-adrenoceptor gene (Arg389Gly), which has functional importance in vitro, was determined in 194 African-Americans, 316 Caucasian-Americans, 221 Hispanic-Americans and 142 Chinese. African-Americans were found to have a significantly lower frequency of the Arg389 allele than the other three ethnic groups (all P < 0.01). In the populations studied, the order of the distribution of the Arg389 allele was: Chinese (74%) > Caucasians (72%) > Hispanics (67%) > African-Americans (58%). To determine the functional significance of the Arg389Gly beta 1-adrenoceptor polymorphism, in-vivo heart rate responses to exercise were compared in healthy subjects homozygous for the Arg (n = 9) and Gly (n = 8) alleles. Heart rate response to exercise was not affected by genotype (P = 0.4). Although ethnic differences in the frequency of the beta 1-adrenoceptor Arg389Gly polymorphism exist, the polymorphism does not appear to have functional significance in healthy subjects and therefore may not contribute to ethnic differences in response to drugs acting through the beta 1-adrenoceptor.

Chronotropic dose response of atropine in Nigerians with congestive heart failure: assessment of ethnic variation and reversibility of parasympathetic dysfunction.

Both ethnicity and disease states may influence cardiac parasympathetic tone. We evaluated the cardiac vagal activity in 9 Nigerians aged 57(11) with congestive heart failure, and 9 age- and sex-matched healthy controls aged 51(11) years, using a cumulative low dose atropine response curve. All subjects demonstrated bradycardia at low doses (100 microg-400 microg) and tachycardia at higher doses (600 microg-1,000 microg). However, both the bradycardic and the tachycardic responses were attenuated in heart failure patients compared to controls: bradycardia -1.1(1.5) beats/min in heart failure patients vs -7.1(2.2) beats/min in controls (P<.01) and tachycardia +4(1.5) beats/min in heart failure patients vs +14.3(3) beats/min in healthy controls (P<.01). EC50 values for brachycardia and tachycardia calculated from the dose response curves were significantly higher in healthy controls compared to heart failure patients, for bradycardia 69(39) microg versus 11(1.6) microg (P<.01) and tachycardia 682(61) microg vs 254(84) microg (P<.01). Treatment of heart failure for 4 weeks with furosemide, digoxin and angiotensin converting enzyme inhibitor (enalapril) caused a significant increase in the magnitude of both the bradycardic responses from -1.1(1.5) beats/min to -4.4(0.9) beats/min after treatment, and tachycardic responses from +4(1.5) beats/min to +10.(2.3) beats/min 4 weeks after treatment (P<.05). After 4 weeks of treatment, EC50 was also increased significantly toward normal values. For tachycardia, the values were 254(88) microg before treatment vs 529(78) microg after treatment (P<.05); and for bradycardia, the values were 2.5(1.6) microg before treatment vs 30(13) microg after treatment (P<.05). These findings demonstrate the early bradycardic effect of atropine in Black Africans (both healthy controls and heart failure patients), contradicting earlier reports of its absence in the negroid race. This confirms the reduction in cardiac parasympathetic responsiveness (both maximal heart rate change and EC50) in hypertensive heart failure using a pharmacological assay. It demonstrates the augmentation and amelioration of cardiac vagal tone with enalapril-dixogin-diuretic therapy in non-ischemic heart failure, and the sequential utility of the low dose atropine-chronotropic response in assessing cardiac parasympathetic activity.

Human beta2-adrenergic receptor polymorphisms: no association with essential hypertension in black or white Americans.

BACKGROUND AND OBJECTIVES: The most common polymorphisms of the human beta2-adrenergic receptor--Arg16-->Gly and Gln27-->Glu--are associated with alterations in beta2-adrenergic receptor responses, both in vitro and in vivo. beta2-Adrenergic receptor-mediated vascular responses are affected by ethnicity, blood pressure, and genotype. We tested the hypothesis that these two common beta2-adrenergic receptor genetic variants are associated with essential hypertension in black or white Americans. SUBJECTS AND METHODS: In a population-based case-control association study, the relationship between beta2-adrenergic receptor genotypes and hypertension was examined in 307 normotensive subjects (128 black and 179 white) and 356 hypertensive subjects (155 black and 201 white). A polymerase chain reaction-based single-stranded conformational polymorphism method with direct sequencing of the bands of interest was used to detect the two frequently occurring beta2-adrenergic receptor variants (Arg16-->Gly, Gln27-->Glu). RESULTS: No significant differences in the distributions of alleles and genotypes of the tested beta2-adrenergic receptor variants were found between normotensive and hypertensive groups from either black or white Americans (all P > .05). There was a marked interethnic difference in the frequency of the Gln27-->Glu beta2-adrenergic receptor polymorphism in both normotensive and hypertensive subjects. In normotensive white subjects, the variant Glu27 allele (35.2% versus 18.0%; P < .0001) and Glu27 homozygous genotype (14.0% versus 4.7%; P < .01) were more common than in black subjects. Similarly, in hypertensive white subjects, the variant Glu27 allele (35.8% versus 18.4%; P < .0001) and the Glu27 homozygous genotype (15.9% versus 2.6%; P < .0001) were more common than in black subjects. CONCLUSIONS: These data suggest that although there are marked ethnic differences in their distribution, the common genetic polymorphisms of the human beta2-adrenergic receptor gene do not cosegregate with the presence of hypertension in either black or white Americans.

Knowledge, attitude and practice of prednisolone prevention of chloroquine induced pruritus among Nigerian health workers.

Severe generalized pruritus is a common drawback in chloroquine therapy of malaria in black Africans. In a cross-sectional study, we evaluated the knowledge, attitude and practice of 117 Nigerian hospital workers, who historically itch to chloroquine, to the use of prednisolone to prevent chloroquine pruritus in malaria. Ninety per cent of respondents had a positive family history of chloroquine induced pruritus. Seventy-five per cent (92) of the subjects were aware of the anti-pruritic action of prednisolone, but only 43% (n = 40) have ever used it during malaria. Among the prednisolone users (n = 40), 25 (62.5%) had total prevention, 25% (n = 10) had marked pruritus attenuation, but no effect was seen in 12.5% (n = 5). The modal prednisolone dose causing inhibition of itching was 10 mg orally given once. Concurrent prednisolone increased compliance with chloroquine in 68% of all who used the combination, and there was no evidence of malaria recurrence.

Vasodilator therapy of hypertensive acute left ventricular failure: comparison of captopril-prazosin with hydralazine-isosorbide dinitrate.

A prospective study to evaluate and compare the cardiorespiratory effects and clinical efficacy of the Neurohormonal inhibitors (Captopril 50 mg+prazosin 1 mg only) and direct arteriolar and venular dilators (Intravenous hydralazine 30 mg+oral isosorbide dinitrate 30 mg) used as vasodilator therapy, was undertaken in a randomized, single blind study in 17 Nigerian patients with hypertensive acute left ventricular failure. Both vasodilator regimes separately and significantly reduced the systolic and diastolic blood pressures (P<0.001 ANOVA), heart rate (P<0.001 ANOVA), and the respiratory rate (P<0.05 ANOVA), the double product, but increased the peak expiratory flow rate (P<0.05 ANOVA). However, the neurohormonal antagonists, captopril and prazosin (n=9) caused a statistically significantly greater reduction in heart rate (P<0.05 ANOVA) respiratory rate (P<0.05 ANOVA) and induced a significantly greater increase in the self-paced exercise capacity, 24 h after initiation of treatment, (P<0.02) compared to the hydralazine and isosorbide dinitrate combination (n=8). Five of the nine patients on the neurohormonal antagonist therapy were ambulant at 24 h, compared to none of the eight patients receiving conventional venular and arteriolar dilators hydralazine and isosorbide dinitrate (chi2=5.84 dfi P<0.05). There was a significant inverse correlation between the systolic blood pressure heart rate product, and the distance covered during symptom limited self paced exercise capacity (r=-0.58, P=0.0146 ANOVA). One of eight patients in the hydralazine+isosorbide nitrate combination died, but there was no mortality in the captopril+prazosin group. These findings collectively suggest that captopril+prazosin combination may be a superior vasodilator therapy compared to hydralazine-isosorbide dinitrate, in hypertensive acute pulmonary oedema.

Chloroquine-induced pruritus in malaria fever: contribution of malaria parasitaemia and the effects of prednisolone, niacin, and their combination, compared with antihistamine.

AIMS: Chloroquine treatment of malaria fever, results in a generalized pruritus of unknown mechanism in up to 60% of adult Africans, by contrast pruritus is unusual in Caucasians following chloroquine use. METHODS: We conducted a double-blind, randomized, parallel group study to examine and compare the antipruritic effects of promethazine, niacin, prednisolone and their combination on pruritus induced by chloroquine, in 28 historical itching patients with parasitologically proven malaria fever. We also evaluated the role of the antecedent malaria parasite density in the severity of chloroquine pruritus intensity. RESULTS: The concurrent administration of chloroquine (2.1 g base total dose) with prednisolone caused a statistically significant reduction in the pruritus AUC (0, 72 h) (P < 0.001 ANOVA) compared with the antihistamine promethazine alone. The areas under the pruritus intensity-time curve were promethazine 105 +/- 28 (units h), niacin 76 +/- 22, prednisolone 28 +/- 24, and prednisolone and niacin 34 +/- 17 (P < 0.001 ANOVA). The 95% confidence interval for the difference in the pruritus AUC between prednisolone and promethazine was 8.4 to 145.6 units h. There was a statistically significant and positive correlation between the pruritus intensity (AUC 0, 72 h) and the malaria parasite load in the itching subjects, not receiving prednisolone (n = 9) (r = 0.73, P = 0.026 ANOVA). CONCLUSION: A single oral dose of prednisolone (10 mg) may be preferable to the antihistamine promethazine (25 mg) as an antipruritic agent for concurrent prescription with chloroquine in individuals predisposed to severe itching. Malaria parasite clearance and clinical amelioration were unaffected by any of the treatments.

Concurrent alpha 1 adrenergic blockade and angiotensin converting enzyme inhibition in the treatment of congestive heart failure.

We tested the hypothesis that concurrent inhibition of the renin angiotensin system by enalapril (5 mg) and the sympathetic nervous system by alpha 1 adrenergic blockade (prazosin 1 mg) will be superior to enalapril alone in 17 patients with heart failure on standard therapy, in a single blind, placebo-controlled, randomized parallel group study for 4 weeks. Enalapril alone induced a significant increase in exercise time from 499 +/- 412 s to 707 +/- 608 s (P < 0.05, ANOVA), but the increase induced by the enalapril + prazosin combination was significantly greater (P < 0.025, MANOVA) from 214 +/- 271 to 1007 +/- 784 s as was the increase in creatinine clearance (P < 0.05).

A double-blind, placebo-controlled study of the efficacy of thiamine hydrochloride in a seasonal ataxia in Nigerians.

We report the results of the first double-blind, placebo-controlled trial of the efficacy of thiamine hydrochloride in a seasonal ataxic syndrome of unknown etiology, endemic to the southwestern part of Nigeria. Thiamine produced a clinically impressive and statistically significant improvement in clinical severity grading in patients with the seasonal ataxia compared with placebo (MANOVA, df = 1, F = 35.087, p < 0.0001), with a significant time-treatment interaction (MANOVA, df = 3, F = 32.36, p < 0.0001). These results provide confirmation for the role of thiamine deficiency in the etiology of the seasonal ataxic syndrome and represent the first advance in the elucidation of the etiology of this syndrome.

An open non-comparative pilot study of the safety and efficacy of oral fluconazole in the treatment of dermatophyte infections in Nigeria

In an non-comparative study to assess the efficacy and safety of oral fluconazole in superficial fungal diseases of the skin; 82 adult Nigerian patients (58 males and 24 females) with clinical and mycological diagnosis of dermatomycoses were enrolled for the trial. Sixty-five patients completed the trial and each of them received a daily dose of 50mg fluconazole for a period of 4 weeks. An overall 90 per cent cure rate was observed in patients with other forms of dermatomycoses and 80 per cent for patients with pityriasis versicolor. The drug was well tolerated by all the patients and very few side effects were noticed