Thorough QT study of the effects of vildagliptin, a dipeptidyl peptidase IV inhibitor, on cardiac repolarization and conduction in healthy volunteers.

OBJECTIVE: This randomized, double-blind study evaluated the effects of vildagliptin, a dipeptidyl peptidase IV inhibitor for treating type 2 diabetes, on cardiac repolarization and conduction. METHODS: Healthy volunteers (n = 101) were randomized (1:1:1:1 ratio) to vildagliptin 100 or 400 mg, moxifloxacin 400 mg (active control), or placebo once daily for 5 days. Electrocardiograms were recorded at baseline and day 5 for 24 hours post-dose. Placebo-adjusted mean change from baseline in QT interval, heart-rate-corrected QT intervals by Fridericia's (QTcF) or Bazett's (QTcB) formula, and PR and QRS intervals were compared at each time-point (time-matched analysis) and for values averaged across the dosing period (time-averaged analysis). RESULTS: For time-matched analysis, mean changes in QTcF with vildagliptin were below predefined limits for QTc prolongation (mean increase <5 ms; upper 90% confidence interval [CI] < 10 ms), except for vildagliptin 100 mg at 1 and 8 hours post-dose (upper 90% CI > 10 ms). With moxifloxacin, significant QTcF prolongation occurred at most time-points, demonstrating assay sensitivity. No vildagliptin- or placebo-treated volunteer had QTcF > 450 ms. Incidences of QTcF increases ≥30 ms with vildagliptin (100 and 400 mg) and placebo were similar (4-8%) and were much lower than with moxifloxacin (39%). No QTcF increase ≥60 ms was observed with vildagliptin or placebo (versus one with moxifloxacin). Time-averaged, time-matched, and categorical analyses of QT/QTcF/QTcB showed similar results. Drug exposure analysis showed no correlation between vildagliptin plasma levels and QTc changes. Vildagliptin had no effect on PR or QRS intervals. Although this study, completed before publication of current ICH E14 guidelines, was underpowered for time-matched analysis, the results are consistent with lack of effect of vildagliptin on QTc. CONCLUSION: Vildagliptin did not prolong QT interval or affect cardiac conduction at the highest daily therapeutic dose or a fourfold higher dose.

Comparative efficacy and safety of aliskiren and irbesartan in patients with hypertension and metabolic syndrome.

Metabolic syndrome, a cluster of risk factors that increase the risk of cardiovascular morbidity and mortality, is common in patients with hypertension. Chronic renin-angiotensin-aldosterone system (RAAS) activation, shown by elevated plasma renin activity (PRA), is implicated in many of the features of metabolic syndrome. The direct renin inhibitor aliskiren may be of benefit in this patient group as aliskiren targets the RAAS at the rate-limiting step. In this double-blind study, 141 patients with hypertension (mean baseline BP 155/93 mm Hg) and metabolic syndrome (modified National Cholesterol Education Program ATP III criteria) were randomized to aliskiren 300 mg or irbesartan 300 mg once daily. Patients treated with aliskiren 300 mg had their mean sitting blood pressure (BP) lowered by 13.8/7.1 mm Hg after 12 weeks, significantly greater (P≤0.001) than the 5.8/2.8 mm Hg reduction observed in patients treated with irbesartan 300 mg. A significantly greater proportion of patients treated with aliskiren achieved BP control to <135/85 mm Hg (29.2 vs 16.7% with irbesartan; P=0.019). Aliskiren treatment led to a 60% decrease in PRA from baseline, whereas irbesartan increased PRA by 99% (both P<0.001). Aliskiren and irbesartan had similar effects on glucose and lipid profiles and on a panel of biomarkers of inflammation and cardiovascular risk. Both aliskiren and irbesartan were well tolerated. Collectively, these results suggest that aliskiren 300 mg may offer treatment benefits compared with irbesartan 300 mg for BP reduction in patients with hypertension and metabolic syndrome.

Evaluation of pharmacokinetic and pharmacodynamic interaction between the dipeptidyl peptidase IV inhibitor vildagliptin, glyburide and pioglitazone in patients with Type 2 diabetes.

BACKGROUND: Vildagliptin is a selective inhibitor of dipeptidyl peptidase IV (DPP-4) that improves glycemic control and pancreatic b-cell function in patients with Type 2 diabetes. Vildagliptin may be an appropriate agent to combine with other antihyperglycemic agents in patients requiring combination therapy to achieve optimal glycemic control. Two studies were performed to determine the potential for pharmacokinetic and pharmacodynamic interactions between vildagliptin and the sulfonylurea, glyburide, or pioglitazone in patients with Type 2 diabetes. METHODS: Two open-label, multiple-dose, 3-period, randomized, crossover studies in patients with Type 2 diabetes were carried out. Steady state drug pharmacokinetics and postprandial plasma glucose and insulin responses were assessed during treatment with vildagliptin 100 mg b.i.d. alone and in combination with glyburide 10 mg q.d. (n = 17) or with vildagliptin 100 mg q.d. alone or in combination with pioglitazone 45 mg q.d. (n = 15). RESULTS: Coadministration of vildagliptin with either glyburide or pioglitazone had no clinically significant effect on the pharmacokinetics of any of the 3 drugs. Changes in AUC and Cmax during combination treatment were small ( pound 15%), and 90% confidence intervals for the geometric mean ratios (drug coadministration/monotherapy) were generally contained within the acceptance range for bioequivalence (0.80 - 1.25). Vildagliptin/glyburide coadministration significantly reduced the area under the plasma glucose-time curve compared with glyburide alone (AUE0-5h reduced by 12% (p = 0.005) and AUE0-15h by 13% (p = 0.003)), and increased the area under the plasma insulin-time curve (AUE0-15h increased by 12% (p = 0.041)). Vildagliptin/pioglitazone coadministration also significantly reduced postprandial glucose exposure compared with pioglitazone alone (AUE0.5-5.5h reduced by 11% (p = 0.029) and AUE0-15.5h by 10% (p = 0.019)). Vildagliptin was generally well tolerated whether administered alone or in combination with glyburide or pioglitazone, and was not associated with hypoglycemia. CONCLUSIONS: Coadministration of vildagliptin with either glyburide or pioglitazone in patients with Type 2 diabetes improves postprandial glycemic control without notable effects on drug pharmacokinetics.

Effect of aliskiren, an oral direct renin inhibitor, on the pharmacokinetics and pharmacodynamics of a single dose of acenocoumarol in healthy volunteers.

OBJECTIVE: Aliskiren is a direct renin inhibitor approved for the treatment of hypertension. This study investigated the effects of aliskiren on the pharmacokinetics and pharmacodynamics of a single dose of acenocoumarol in healthy volunteers. METHODS: This two-sequence, two-period, randomized, double-blind crossover study recruited 18 healthy subjects (ages 18-45) to receive either aliskiren 300 mg or placebo once daily on days 1-10 of each treatment period and a single dose of acenocoumarol 10 mg on day 8. Treatment periods were separated by a 10-day washout. Blood samples were taken frequently for determination of steady-state plasma concentrations of aliskiren (LC-MS/MS) and of R(+)- and S(-)-acenocoumarol (HPLC-UV), prothrombin time (PT) and international normalized ratio (INR). RESULTS: Co-administration with aliskiren had no effect on exposure to R(+)-acenocoumarol. Geometric mean ratios (GMR; aliskiren:placebo co-administration) for R(+)-acenocoumarol AUC(0-t) and C(max) were 1.08 and 1.04, respectively, with 90% CI within the range 0.80-1.25. Co-administration of aliskiren resulted in a 19% increase in S(-)-acenocoumarol AUC(0-t) (GMR 1.19; 90% CI 0.92, 1.54) and a 9% increase in C(max) (GMR 1.09; 90% CI 0.88, 1.34). The anticoagulant effect of acenocoumarol was not affected by co-administration of aliskiren. Geometric mean ratios were 1.01 for all pharmacodynamic parameters (AUC(PT), PT(max), AUC(INR) and INR(max)), with 90% CI within the range 0.97-1.05. CONCLUSION: Aliskiren has no clinically relevant effect on the pharmacokinetics or pharmacodynamic effects of a single dose of acenocoumarol in healthy volunteers, hence no dosage adjustment of acenocoumarol is likely to be required during co-administration with aliskiren.

A study of dose-proportionality in the pharmacokinetics of the oral direct renin inhibitor aliskiren in healthy subjects.

OBJECTIVE: To evaluate the dose-proportionality of the pharmacokinetics of aliskiren, the first in a new class of orally active direct renin inhibitors approved for the treatment of hypertension. METHODS: This was an open-label, single-center, single-dose, randomized, 4-period crossover study. Following a 21-day screening period, 32 healthy male or female subjects (ages 18 - 45 years) were randomized to 1 of 4 aliskiren dosing sequence groups (8 subjects per group): 75, 150, 300 and 600 mg. Blood samples were obtained for determination of plasma aliskiren concentrations (HPLC/MS/MS) for 96 h post dose. Log-transformed pharmacokinetic parameters AUC and C(max) were analyzed to determine dose-proportionality using the power model, parameter = A*(Dose)(beta), where A = intercept and beta = dose-proportionality coefficient. The predefined dose-proportionality criteria over the dose range 75 â 600 mg were 90% confidence intervals (CI) for beta contained within the range 0.89 - 1.11. RESULTS: AUC and Cmax values increased with increasing doses of aliskiren. Both AUC and C(max) were associated with high variability (coefficient of variation 55 - 64% for AUC and 59 - 117% for C(max)). The estimated proportionality coefficients (beta) for AUC(0-infiniti), AUC(0-t) and C(max) were 1.18 (90% CI 1.10, 1.25), 1.29 (90% CI 1.22, 1.36) and 1.42 (90% CI 1.31, 1.52), respectively. Dose-proportionality was, therefore, not demonstrated across the entire 8-fold dose range. For the clinical dose range of 150 â 300 mg, increases of 2.3- and 2.6-fold were observed for AUC and C(max), respectively. All doses of aliskiren were well tolerated. CONCLUSIONS: Exposure to aliskiren was greater than proportional over the dose range of 75 - 600 mg. Over the therapeutic dose range of 150 â 300 mg approved for the treatment of hypertension, AUC and Cmax increased by 2.3- and 2.6-fold, respectively. The pharmacokinetics of aliskiren show relatively high intersubject variability.

Overexpression of PAI-1 prevents the development of abdominal aortic aneurysm in mice.

Vessel wall inflammation and matrix destruction are critical to abdominal aortic aneurysm (AAA) formation and rupture. We have previously shown that urokinase plasminogen activator (uPA) is highly expressed in experimental AAA and is essential for AAA formation and expansion. In this study, we examined the effects of overexpression of a natural inhibitor of uPA, plasminogen activator inhibitor-1 (PAI-1), on the development of angiotensin (Ang) II-induced AAA in ApoE-deficient (ApoE(-/-)) mice. Mice were treated with recombinant adenovirus containing either the human PAI-1 gene (Ad5.CMV.PAI-1) or the luciferase gene (Ad5.CMV.Luc) delivered either locally by intra-adventitial injection or systemically by tail vein injection. Our results show that local delivery of the PAI-1 gene completely prevented AAA formation (0 vs 55.6% in Ad5.CMV.Luc controls, P<0.05). In contrast, systemic delivery of the PAI-1 gene did not affect AAA incidence (78 vs 90% in Ad5.CMV.Luc controls, P=0.125). Local delivery of the PAI-1 gene 2 weeks after Ang II infusion prevented further expansion of small aneurysms, but had no significant effect on the progression of larger aneurysms. These data suggest that local PAI-1 gene transfer could be used to stabilize small AAA and reduce the rate of expansion and risk of rupture.

The influence of hepatic impairment on the pharmacokinetics of the dipeptidyl peptidase IV (DPP-4) inhibitor vildagliptin.

OBJECTIVE: Vildagliptin is a potent and selective dipeptidyl peptidase-IV (DPP-4) inhibitor that improves glycemic control in patients with type 2 diabetes mellitus by increasing alpha- and beta-cell responsiveness to glucose. This study investigated the pharmacokinetics of vildagliptin in patients with hepatic impairment compared with healthy subjects. METHODS: This was an open-label, parallel-group study in patients with mild (n = 6), moderate (n = 6) or severe (n = 4) hepatic impairment and healthy subjects (n = 6). All subjects received a single 100-mg oral dose of vildagliptin, and plasma concentrations of vildagliptin and its main pharmacologically inactive metabolite LAY151 were measured up to 36 h post-dose. RESULTS: Exposure to vildagliptin (AUC(0-infinity) and C(max)) decreased non-significantly by 20 and 30%, respectively, in patients with mild hepatic impairment [geometric mean ratio (90% CI): AUC(0-infinity), 0.80 (0.60, 1.06), p = 0.192; C(max), 0.70 (0.46, 1.05), p = 0.149]. Exposure to vildagliptin was also decreased non-significantly in patients with moderate hepatic impairment [-8% for AUC(0-infinity), geometric mean ratio (90% CI): 0.92 (0.69, 1.23), p = 0.630; -23% for C(max), geometric mean ratio (90% CI): 0.77 (0.51, 1.17), p = 0.293]. In patients with severe hepatic impairment, C(max) was 6% lower than that in healthy subjects [geometric mean ratio (90% CI): 0.94 (0.59, 1.49), p = 0.285], whereas AUC(0-infinity) was increased by 22% [geometric mean ratio (90% CI): 1.22 (0.89, 1.68), p = 0.816). Across the hepatic impairment groups, LAY151 AUC(0-infinity) and C(max) were increased by 29-84% and 24-63%, respectively, compared with healthy subjects. The single 100-mg oral dose of vildagliptin was well tolerated by patients with hepatic impairment. CONCLUSIONS: There was no significant difference in exposure to vildagliptin in patients with mild, moderate or severe hepatic impairment; therefore, no dose adjustment of vildagliptin is necessary in patients with hepatic impairment.

Lack of pharmacokinetic interactions of aliskiren, a novel direct renin inhibitor for the treatment of hypertension, with the antihypertensives amlodipine, valsartan, hydrochlorothiazide (HCTZ) and ramipril in healthy volunteers.

Aliskiren is a novel, orally active direct renin inhibitor that lowers blood pressure alone and in combination with existing antihypertensive agents. As aliskiren does not affect cytochrome P450 enzyme activities, is minimally metabolised, and is not extensively protein bound, the potential for drug interactions is predicted to be low. Four open-label studies investigated the pharmacokinetic interactions between aliskiren 300 mg and the antihypertensive drugs amlodipine 10 mg (n = 18), valsartan 320 mg (n = 18), hydrochlorothiazide 25 mg (HCTZ, n = 22) and ramipril 10 mg (n = 17) in healthy subjects. In each study, subjects received multiple once-daily doses of aliskiren and the test antihypertensive drug alone or in combination in two dosing periods separated by a drug-free washout period. Plasma concentrations of drugs were determined by liquid chromatography and mass spectrometry methods. At steady state, relatively small changes in exposure to aliskiren were observed when aliskiren was co-administered with amlodipine (AUC(tau) increased by 29%, p = 0.032), ramipril (C(max,ss) increased by 31%, p = 0.043), valsartan (AUC(tau) decreased by 26%, p = 0.002) and HCTZ (C(max,ss) decreased by 22%, p = 0.039). Co-administration with aliskiren resulted in small changes in exposure to ramipril (AUC(tau) increased by 22%, p = 0.002), valsartan (AUC(tau) decreased by 14%, p = 0.062) and HCTZ (AUC(tau) decreased by 10% and C(max,ss) by 26%, both p < 0.001). All other changes in pharmacokinetic parameters were also small, and not statistically significant. None of the observed pharmacokinetic changes was considered clinically relevant. Aliskiren inhibited plasma renin activity (PRA) and also prevented the reactive rise in PRA induced by valsartan. The most commonly reported adverse events were headache, dizziness and gastrointestinal symptoms (all mild in severity), which were similar in frequency during antihypertensive drug treatment alone and in combination with aliskiren except for an increase in dizziness during treatment with the combination of aliskiren and HCTZ. In conclusion, aliskiren shows no clinically relevant pharmacokinetic interactions and is generally well tolerated when administered in combination with amlodipine, valsartan, HCTZ or ramipril.

Effective treatment of vascular endothelial growth factor refractory hindlimb ischemia by a mutant endothelial nitric oxide synthase gene.

Gene delivery of angiogenic growth factors is a promising approach for the treatment of ischemic cardiovascular diseases. However, success of this new therapeutic principle is hindered by the lack of critical understanding as to how disease pathology affects the efficiency of gene delivery and/or the downstream signaling pathways of angiogenesis. Critical limb ischemia occurs in patients with advanced atherosclerosis often exhibiting deficiency in endothelial nitric oxide production. Similar to these patients, segmental femoral artery resection progresses into severe ischemic necrosis in mice deficient in endothelial nitric oxide synthase (ecNOS-KO) as well as in balb/c mice. We used these models to evaluate the influence of severe ischemia on transfection efficiency and duration of transgene expression in the skeletal muscle following plasmid injection in combination with electroporation. Subsequently, we also explored the potential therapeutic effect of the phosphomimetic mutant of ecNOS gene (NOS1177D) using optimized delivery parameters, and found significant benefit both in ecNOS-KO and balb/c mice. Our results indicate that NOS1177D gene delivery to the ischemic skeletal muscle can be efficient to reverse critical limb ischemia in pathological settings, which are refractory to treatments with a single growth factor, such as vascular endothelial growth factor.

Angiotensin II increases urokinase-type plasminogen activator expression and induces aneurysm in the abdominal aorta of apolipoprotein E-deficient mice.

Urokinase-type plasminogen activator (uPA) is increased in human abdominal aortic aneurysm (AAA). Chronic infusion of angiotensin II (Ang II) results in AAA in apolipoprotein E-deficient mice. We tested the hypothesis that Ang II infusion results in an elevation of uPA expression contributing to aneurysm formation. Ang II or vehicle was infused by osmotic pumps into apoE-KO mice. All mice treated with Ang II developed a localized expansion of the suprarenal aorta (75% increase in outer diameter), accompanied by an elevation of blood pressure (22 mmHg), compared to the vehicle-treated group. Histological examination of the dilated aortic segment revealed similarities to human AAA including focal elastin fragmentation, macrophage infiltration, and intravascular hemorrhage. Ang II treatment resulted in a 13-fold increase in the expression of uPA mRNA in the AAA segment in contrast to a twofold increase in the atherosclerotic aortic arch. Increased uPA protein was detected in the abdominal aorta as early as 10 days after Ang II infusion before significant aorta expansion. Thus, Ang II infusion results in macrophage infiltration, increased uPA activity, and aneurysm formation in the abdominal aorta of apoE-KO mice. These data are consistent with a causal role for uPA in the pathogenesis of AAA.

Effect of acute hypertension in the coronary circulation: role of mechanical factors and oxygen radicals.

OBJECTIVE: In previous studies severe, acute hypertension damaged the endothelium in proximal coronary arteries and selectively potentiated constriction of the artery to serotonin. In the present study we investigated the role of several mechanical factors and of oxygen radicals in this response. DESIGN: To test the role of mechanical factors in the response to acute hypertension, the effect of different magnitudes of elevation of perfusion pressure and the rate of the rise in perfusion pressure were studied. Pharmacologically induced increases in blood pressure were produced by infusion of angiotensin II or phenylephrine. The role of oxygen radicals was tested by measuring responses to serotonin before and after increases in perfusion pressure in dogs treated with a combination of superoxide dismutase and catalase or with deferoxamine. METHODS: In open-chest anesthetized dogs the diameter of the left anterior descending coronary artery (LADCA) was measured using sonomicrometer crystals, and the LADCA was perfused at a constant pressure of 80 mmHg from a reservoir. Responses to serotonin were measured at this perfusion pressure before and after an abrupt increase in perfusion pressure. RESULTS: Intracoronary serotonin (5 or 50 micrograms/min) produced a dose-dependent constriction of the LADCA while increasing coronary flow. Abruptly increasing the coronary perfusion pressure from 80 to 120, 150 or 200 mmHg augmented the constriction to serotonin twofold, whereas increases in perfusion pressure to 100 mmHg had no effect. Increasing coronary pressure slowly (over a 4-min period) from 80 to 200 mmHg augmented constriction to serotonin. Inducing acute hypertension (coronary pressure 200 mmHg) pharmacologically with angiotensin II also augmented constriction to serotonin, whereas phenylephrine-induced hypertension did not. Superoxide dismutase, a scavenger of superoxide anions and catalase, a scavenger of hydrogen peroxide, prevented the augmented constriction to serotonin following a pressure increase. Deferoxamine, which prevents generation of hydroxyl radicals from superoxide anions and hydrogen peroxide, also prevented the enhanced constriction to serotonin following an acute pressure increase. CONCLUSIONS: Moderate physiological increases in pressure, induced either mechanically or pharmacologically, can augment the responses to serotonin. Oxygen-derived free radicals, particularly hydroxyl radicals, might be involved in the abnormal response to serotonin following an abrupt increase in coronary pressure.

Intravenous iloprost treatment of Raynaud's phenomenon and ischemic ulcers secondary to systemic sclerosis.

OBJECTIVE: We conducted this study to assess the clinical usefulness and physiologic effects of intravenous iloprost in patients with Raynaud's phenomenon secondary to systemic sclerosis. METHODS: Thirty-five patients with Raynaud's phenomenon secondary to systemic sclerosis, including 11 with digital ischemic ulcerations, were enrolled in a double blind placebo controlled parallel study in 2 centers. Following a 2 week washout, subjects received intravenous iloprost (0.5-2.0 ng/kg/min) or saline by continuous infusion for 6 h on 5 consecutive days. Clinical assessments, status of digital ulcers, measures of in vivo platelet activation and detailed studies of peripheral vascular response to cold challenge, were performed at entry, at 5 days of therapy and at biweekly intervals for 10 weeks. RESULTS: Complete healing of all cutaneous lesions (ulcers, fissures, and paronychia) was observed 10 weeks after treatment in 6 of 7 patients receiving iloprost versus none of 4 receiving placebo (p = 0.015). Ischemic digital tip ulcers completely healed in all 4 patients with ulcers in the iloprost group, but none in the placebo group (p = 0.029). Patient diaries of frequency, duration and symptoms of Raynaud's phenomenon showed improvement in both groups. Critical ischemic temperature (finger temperature during controlled cold challenge at which Raynaud's or loss of detectable digital blood flow occurred) progressively decreased in the iloprost group from 21.3 +/- 7.3 degrees C at baseline to a minimum of 16.1 +/- 3.2 degrees C at 8 weeks after treatment (p = 0.076), whereas no consistent changes were observed in the placebo group. Treatment was associated with improvement in the rate of skin temperature recovery following cold challenge. No changes were noted in ambient digital skin temperature, total digital blood flow, finger systolic pressure or in measures of in vivo platelet activation. One subject dropped out with chest pain, but adverse effects of nausea, vomiting, headache and jaw pain were otherwise limited to the 5 days of drug infusion. CONCLUSION: Iloprost appears useful for the treatment of digital ulcers in systemic sclerosis and is associated with evidence of prolonged physiologic improvement although the mechanism of this effect remains unclear.

Iloprost in cardiopulmonary bypass procedures.

The inhibition of platelet aggregation during cardiopulmonary bypass and effects on post-operative placebo-controlled study of 145 patients. Significant preservation of platelet numbers and function were shown without significant haemodynamic problems, but no effect on cerebral deficits could be found. The use of iloprost in patients with severe thrombocytopenia seems justified, but the clinical benefits from its use in routine cardiopulmonary bypass remain to be shown.

Adenosine receptor blockade enhances isoproterenol-induced increases in cardiac interstitial adenosine.

The failure of adenosine receptor antagonists to consistently attenuate metabolic coronary vasodilation suggests that adenosine is not a primary regulator of functional hyperemia. An alternative hypothesis, however, is that metabolic stimulation of the heart in the presence of an adenosine receptor antagonist results in enhanced interstitial levels of adenosine which then might overcome the blockade. To test this hypothesis, interstitial levels of adenosine and inosine were estimated by HPLC analysis of fluid which exudes from the epicardial surface of isolated rat hearts perfused with crystalloid solution at constant flow. Isoproterenol infusion (10 nM) produced increases in heart rate, left ventricular systolic pressure, rate of pressure development, myocardial oxygen consumption and adenosine and inosine concentrations of venous effluent and surface exudate and produced decreases in coronary vascular resistance. The presence of the adenosine receptor antagonist, 8-(4-sulfophenyl) theophylline (spT) (100 microM), in the perfusate had little or no effect upon most of the responses to isoproterenol except that it significantly enhanced the isoproterenol-induced increases in adenosine release and adenosine concentrations in the venous effluent and surface exudate. The isoproterenol-induced change in adenosine concentration per unit change in oxygen consumption was approximately 3-fold greater in the presence of spT than in its absence. This extra adenosine production may tend to overcome the competitive blocking effect of spT and help explain why agents such as spT are not always effective in blocking metabolic vasodilation.

Failure of vasoldilator infusion to alter pulmonary diffusing capacity in systemic sclerosis.

PURPOSE: Patients with systemic sclerosis (SSc) do not exhibit a normal increase in the diffusing capacity for carbon monoxide (DLCO) on assuming the supine position. We sought to determine whether a potent prostacyclin derivative and vasodilator, iloprost, would reverse this defect. PATIENTS AND METHODS: Fourteen patients with SSc were enrolled in a randomized, double-blind, placebo-controlled study of iloprost. Patients were tested before and during 3 days of iloprost or placebo infusion with both upright and supine pulmonary function studies. RESULTS: The results of baseline pulmonary function studies including DLCO were not significantly altered by iloprost. Furthermore, iloprost did not alter the abnormal postural DLCO response. CONCLUSION: These results suggest that the pulmonary vascular defects seen in this group of patients are not a consequence of reversible pulmonary vasospasm.

Role of endothelium-derived relaxing factor and prostaglandins in responses of coronary arteries to thromboxane in vivo.

We examined the relative contribution of endothelial and vascular smooth muscle-derived prostaglandins and endothelium-derived relaxing factor in modulating both the large coronary artery and resistance vessel responses to thromboxane in vivo. Vascular responses to the thromboxane analogue U46619 were measured in four separate experimental protocols: 1) The vascular responses were measured in the presence and absence of intact endothelium to examine the role of endothelium-derived vasodilators. 2) Responses were measured in the presence of intact endothelium before and after inhibition of cyclooxygenase with indomethacin to examine the role of endothelial and vascular smooth muscle-derived prostaglandins. 3) Responses were measured after endothelial removal before and after indomethacin to examine the role of vascular smooth muscle-derived prostaglandins. 4) Responses were measured after indomethacin and before and after removal of endothelium to examine the role of endothelium-derived relaxing factor. In anesthetized dogs (n = 41) that underwent constant pressure perfusion of the left anterior descending coronary artery (LAD), LAD diameter was measured with sonomicrometer crystals, and coronary flow was measured with an electromagnetic flow probe. Intracoronary infusion of U46619 (0.01-1.0 microgram/min) produced a dose-dependent constriction of LAD. Constriction of the LAD was augmented after endothelial removal, after indomethacin treatment in both the presence and absence of endothelium, and after removal of the endothelium in the presence of indomethacin. Inhibition of prostaglandin synthesis had the greatest effect of augmenting constriction of LAD to thromboxane. Coronary flow was decreased by U46619 only in the presence of indomethacin.(ABSTRACT TRUNCATED AT 250 WORDS)

Flow-mediated dilation attenuates constriction of large coronary arteries to serotonin.

We tested the hypothesis that flow-mediated endothelium-dependent dilation can attenuate humorally mediated constriction of large coronary arteries in vivo. Accordingly, we measured constriction of large coronary arteries to serotonin when flow was allowed to increase and when flow was constant in the presence and absence of endothelium. The left anterior descending coronary artery of anesthetized dogs was perfused at constant pressure (100 mmHg) and diameter measured with an ultrasonic dimension gauge. Coronary flow was measured with an in-line electromagnetic flow probe. Flow-mediated dilation was demonstrated by measuring diameter (D) after increased flow in response to adenosine (1 mg/min ic). Adenosine (n = 9) increased flow (341 +/- 69%) and resulted in large artery dilation [diameter change (delta D) = 101 +/- 54 microns], which was abolished by maintaining constant flow (distal snare) or by removing endothelium. Serotonin (n = 9, 50 micrograms/min ic) increased flow (298 +/- 45%) while simultaneously decreasing large artery diameter (delta D = -58 +/- 22 microns). When flow was kept constant, serotonin produced a greater constriction (delta D = -173 +/- 29 microns). After the removal of endothelium (n = 10), constrictor responses to serotonin were similar when flow increased (delta D = -84 +/- 13 microns) and when flow was kept constant (delta D = -79 +/- 23 microns). We conclude that flow-mediated dilation of large coronary arteries can attenuate constriction to serotonin and that this effect is dependent on endothelium.

Acute hypertension selectively potentiates constrictor responses of large coronary arteries to serotonin by altering endothelial function in vivo.

We tested the hypothesis that acute coronary artery hypertension may damage vascular endothelium and alter vasomotor responses to humoral agents. We examined effects of intracoronary infusion of the endothelium-dependent agent serotonin and two endothelium-independent agents, angiotensin II and methoxamine, on large coronary artery diameter in the blood perfused dog heart. Responses were examined before and 30 minutes after brief periods of coronary hypertension (200 mm Hg for 10 seconds to 15 minutes). In open-chest anesthetized dogs, the left anterior descending coronary artery was perfused at constant pressure. Coronary diameter (D) was measured with piezoelectric crystals. At a control perfusion pressure of 80 mm Hg, serotonin produced dose-dependent constriction of the large coronary artery (mean +/- SEM; delta D = -22 +/- 10 microns at 5 micrograms/min; -108 +/- 50 microns at 50 micrograms/min). Increasing perfusion pressure to 200 mm Hg increased flow 515 +/- 79% and coronary diameter 509 +/- 9 microns. After 15 minutes of hypertension, when coronary diameter had returned to baseline values, the constriction of the large artery to serotonin was potentiated (delta D = -89 +/- 33 microns at 5 micrograms/min; -207 +/- 45 microns at 50 micrograms/min; p less than 0.05). Hypertension for 1-5 minutes potentiated constrictor responses of large coronary arteries for at least 2 1/2 hours. Removal of endothelium prevented effects of hypertension on constrictor responses of large arteries to serotonin. Hypertension did not alter constrictor responses to angiotension II (1 and 2.5 micrograms/min) or methoxamine (50 and 100 micrograms/min) or the dilator response to acetylcholine (40 micrograms/min). Acute hypertension altered endothelial morphology. There were small endothelial craters following 10 seconds of hypertension, and disruption of endothelial junctions with leukocyte adherence following 1-15 minutes of hypertension. We conclude that acute hypertension alters constrictor responses of large coronary arteries to serotonin by impairing endothelial function and not by directly affecting vascular smooth muscle. These effects of acute hypertension on vascular reactivity are selective in that they do not involve non-endothelium-dependent agents or the endothelium-dependent agent, acetylcholine. The effect of hypertension also persists long after pressure is restored to normotensive levels.