Biomedical subjects

Richard A Preston

Publications and source records attributed to Richard A Preston.

14 recordsLinked to original sources

PubMed2006

Elevated platelet P-selectin expression and platelet activation in high risk patients with uncontrolled severe hypertension.

BACKGROUND: Uncontrolled severe hypertension is associated with alarming rates of cardiovascular events but the mechanisms of vascular injury are not well understood. Recent investigative interest has focused on platelet activation and platelet P-selectin (CD62P) as direct mediators of vascular inflammation and injury. We investigated the association of extreme blood pressure (BP) elevation with platelet P-selectin and fibrinolytic markers in high risk patients with severe hypertension. METHODS: Cross-sectional comparison of platelet CD62, tissue plasminogen activator antigen (tPA), and plasminogen activator inhibitor-1 activity (PAI-1) among 3 BP groups: untreated severely hypertensive patients (SHT; n=18), untreated mildly hypertensive patients (MHT; n=19), and normotensive controls (NT; n=16). RESULTS: Platelet CD62 was greatest in SHT (p=0.00008) and showed a strong correlation with both systolic (p=0.0002, r=0.52) and diastolic (p=0.0003, r=0.52) BP. tPA was greater in SHT than MHT or NT (ANOVA; p=0.02) and correlated with diastolic BP but not SBP. PAI-1 did not correlate with either SBP or DBP but was related to body mass index, diabetes, and dyslipidemia. CONCLUSIONS: Platelet CD62 demonstrated a strong and graded association with both systolic and diastolic BP that persisted in the presence of multiple concomitant risk factors. The association of BP with CD62P was stronger than with either PAI-1 or tPA-Ag. Platelet activation and platelet CD62 increase in a BP-dependent manner and this relationship persists at extreme levels of BP. Platelet activation and platelet CD62 may participate in the accelerated target organ injury observed in high risk patients with severe hypertension.

Blood Pressure↗

PubMed2005

Antihypertensive effects of drospirenone with 17beta-estradiol, a novel hormone treatment in postmenopausal women with stage 1 hypertension.

BACKGROUND: Drospirenone (DRSP) is a novel progestin with antimineralocorticoid activity that has been developed for hormone therapy in combination with 17beta-estradiol (E2) in postmenopausal women. In prior studies with DRSP in postmenopausal women that were focused on relief of menopausal symptoms, DRSP/E2 yielded significant reductions in blood pressure (BP). METHODS AND RESULTS: The effects of 3 mg DRSP/1 mg E2 on clinic and 24-hour ambulatory BP as well as potassium homeostasis were evaluated in postmenopausal women with stage 1 hypertension (systolic, 140 to 159 and/or diastolic, 90 to 99 mm Hg) in a 12-week, multicenter, double-blind, randomized, placebo-controlled study. Clinic BPs were measured at baseline and at 2, 4, 6, 8, and 12 weeks of therapy, whereas potassium was measured at 2, 6, and 12 weeks of therapy. Ambulatory BP was performed in a substudy at baseline and at the end of the trial. In the intention-to-treat population of 213 women, the clinic BP was reduced significantly on DRSP/E2 (clinic BP, -14.1/-7.9 for DRSP/E2 versus -7.1/-4.3 mm Hg for placebo, P<0.0001). In the subgroup of 43 women with ambulatory BP monitoring, the 24-hour BP fell by -8.5/-4.2 mm Hg versus -1.8/-1.6 mm Hg on placebo (P=0.002/0.07). There were no significant changes from baseline in potassium levels or in the incidence of hyperkalemia (> or =5.5 meq/L) on DRSP/E2 compared with placebo. CONCLUSIONS: Combination therapy with DRSP/E2 significantly lowered both clinic and 24-hour systolic BP in postmenopausal women with stage 1 systolic hypertension. This characteristic may lead to benefit for cardiovascular risk reduction in this population.

Aged↗

PubMed2005

Effects of drospirenone/17-beta estradiol on blood pressure and potassium balance in hypertensive postmenopausal women.

BACKGROUND: Drospirenone (DRSP) is a novel progestin with aldosterone receptor antagonist activity developed for hormone therapy as DRSP /17-beta estradiol (DRSP/E2). Because of a significant aldosterone antagonist activity, we studied the effects of DRSP/E2 on serum potassium (K) and blood pressure (BP) in hypertensive postmenopausal women with and without diabetes mellitus. METHODS: This was a multicenter trial in postmenopausal women 44 to 70 years of age, either with type 2 diabetes mellitus (n = 82) or without type 2 diabetes mellitus (n = 148) and using an angiotensin-converting enzyme (ACE) inhibitor or angiotensin II receptor antagonist. Patients were randomized to 28 days of DRSP/E2 or placebo. Study endpoints were the number and percentage subjects who developed hyperkalemia (K >or= 5.5 mEq/L) and changes from baseline in clinic systolic and diastolic BP. To increase the likelihood of unmasking hyperkalemia, the nondiabetic group was also administered ibuprofen for 5 days. RESULTS: There were no statistical differences in the overall number and percentage of subjects with hyperkalemia for DRSP/E2 versus placebo. No subject had symptoms or electrocardiographic changes related to hyperkalemia. Blood pressure was reduced by -8.6/-5.8 mm Hg in patients receiving DRSP/E2 versus -3.7/-2.9 mm Hg in those receiving placebo (P < .01 for both SBP and DBP). CONCLUSIONS: In hypertensive postmenopausal women, treatment with DRSP/E2 was not associated with a greater incidence of hyperkalemia than with placebo in patients with and without type 2 diabetes mellitus and concomitant use of ACE inhibitors, angiotensin receptor antagonists, or ibuprofen. Furthermore, DRSP/E2 was found to have a significant antihypertensive effect in this high-risk population.

Administration, Oral↗

PubMed2004

Advanced glycation end-product cross-link breakers. A novel approach to cardiovascular pathologies related to the aging process.

Advanced glycation end product (AGE) formation that occurs with aging and diabetes leads to the cross-linking of proteins and subsequent changes in the physicochemical properties of tissues. Cellular responses to AGE that lead to either pathological conditions or removal of AGE are mediated by a number of receptors that have been identified on various cell types such as macrophages, endothelial cells, and smooth-muscle cells. Mechanisms by which AGE affect the cardiovascular system include AGE cross-linking of long-lived proteins such as collagen and elastin and altered cellular responses. Alagebrium (3-phenacyl-4,5-dimethylthiazolium chloride, ALT-711) is the first drug in a new class of thiazolium therapeutic agents that break established AGE cross-links between proteins. In animal studies, alagebrium was effective in reducing large artery stiffness, slowing pulse-wave velocity, enhancing cardiac output, and improving left ventricular diastolic distensibility. In human studies to determine safety and efficacy, alagebrium was safe and well tolerated. In the first phase 2 clinical study, alagebrium improved arterial compliance in elderly patients with vascular stiffening. In two subsequent phase 2 clinical studies, one addressing diastolic heart failure and the other addressing systolic hypertension, alagebrium was effective in improving cardiac function and uncontrolled systolic blood pressure, particularly in more severely affected patients. Additional clinical studies to determine the utility of alagebrium in treating cardiovascular disorders associated with aging are in progress.

Aging↗

PubMed2003

Effects of severe hypertension on endothelial and platelet microparticles.

The molecular mechanisms by which extreme blood pressure elevation leads to vascular injury are not defined. To explore the hypothesis that activation of endothelium and platelets as manifested by increased concentrations of circulating endothelial microparticles and platelet microparticles could play a role in this target organ injury, we conducted a cross-sectional study of these markers in 3 groups: (1) untreated patients referred specifically for treatment of severe uncontrolled hypertension; (2) untreated patients with established mild hypertension; and (3) normotensive volunteer subjects. By ANOVA, endothelial (P=0.002) and platelet (P=0.01) microparticles were greatest in the severely hypertensive group. There was a significant correlation between both of these markers and blood pressure, even in the setting of multiple risk factors. Our results suggest that these markers may be useful and specific for pressure-induced endothelial and platelet activation in hypertension. Furthermore, because of the combined effects of endothelial and platelet microparticles on coagulation, leukocytes, and endothelium, it is possible that they may play a pathogenic role in mediating target organ injury in severe hypertension.

Adult↗

PubMed2003

Short-term, high-dose pamidronate-induced acute tubular necrosis: the postulated mechanisms of bisphosphonate nephrotoxicity.

A 76-year-old man had biopsy-proven acute tubular necrosis (ATN) after intravenous administration of 3 doses of 60 mg of pamidronate (Aredia) over a 2-week period. Pamidronate was given to treat hypercalcemia of unknown etiology. Other potential causes of acute renal failure were excluded with appropriate investigations. The patient's preexisting renal impairment in the context of high-doses of pamidronate might have been a potentiating factor for nephrotoxicity. The ATN encountered in this patient resolved; however, short-term hemodialysis was needed. To the best of our knowledge, this is the first reported case of short-term, high-dose pamidronate-induced ATN in the absence of concomitant nephrotoxins. Although necrotic and apoptotic cell death after bisphosphonate administration has been seen in a variety of cells, the exact mechanism of nephrotoxicity is unknown. This report presents a case of pamidronate-induced ATN and discusses the potential mechanisms of bisphosphonate-induced nephrotoxicity.

Aged↗

PubMed2002

Additive effect of drospirenone/17-beta-estradiol in hypertensive postmenopausal women receiving enalapril.

BACKGROUND: Aldosterone has been implicated in the pathogenesis of progressive cardiovascular disease. Drospirenone (DRSP) is a novel progestin with aldosterone receptor antagonist activity developed for hormone replacement therapy (HRT) as DRSP/17beta-estradiol (DRSP/ E2). We investigated the additive effect of DRSP/E2 versus placebo on 24-h ambulatory blood pressure (BP) in postmenopausal women with hypertension treated with enalapril maleate (ENA). METHODS: This was a double-blind, randomized, two-parallel group trial. Twenty-four nonsmoking postmenopausal women receiving 10 mg of ENA twice a day before study were randomized to DRSP/E2 + ENA (n = 12) or placebo (P) + ENA (n = 12) for 14 days. Twenty-four-hour ambulatory BP, plasma renin activity, and serum aldosterone were determined at baseline and on day 14. RESULTS: Compared to placebo, 24-h mean [SD] BP in the DRSP/E2 + ENA group decreased significantly from baseline (139/80 mm Hg), systolic (-9 [51 mm Hg, P = .014) and diastolic (-5 [4] mm Hg, P = .007). Essentially no change from baseline (139/83 mm Hg) in systolic or diastolic 24-h ambulatory BP were observed in the P + ENA group. Aldosterone (mean [SD]) increased from baseline by 2.6 [4.5] ng/dL in the DRSP/E2 + ENA group, and decreased by 0.3 [5.5] ng/dL in the P + ENA group (P = .08) consistent with an antimineralocorticoid effect. CONCLUSIONS: Our results suggest a significant additive BP-lowering effect of DRSP/E2 on both systolic and diastolic BP in hypertensive postmenopausal women receiving ENA, consistent with an antimineralocorticoid effect. DRSP/E2, a HRT with antimineralocorticoid effects, could offer a novel potential mechanism for reducing cardiovascular end points in postmenopausal women.

Aldosterone↗

PubMed2002

Effects of severe, uncontrolled hypertension on endothelial activation: soluble vascular cell adhesion molecule-1, soluble intercellular adhesion molecule-1 and von Willebrand factor.

OBJECTIVES: The molecular mechanisms whereby severe, uncontrolled hypertension (SHT) is translated into acute vascular target organ dysfunction have not been completely defined. We sought to determine whether SHT is associated with pressure-dependent endothelial activation as assessed by soluble vascular cell adhesion molecule-1 (sVCAM-1), soluble intercellular adhesion molecule-1 (sICAM-1) and von Willebrand Factor (vWF). METHODS: We determined sVCAM-1, sICAM-1 and vWF in three groups: (i) untreated patients referred specifically for treatment of SHT [diastolic blood pressure (DBP) > or = 120 mm Hg; n = 24]; (ii) untreated patients with established mild hypertension (MHT; DBP 95-100 mmHg; n = 19); and (iii) normotensive volunteers (DBP < or = 90; n = 16). RESULTS: By analysis of variance, sVCAM-1 (P = 0.002), sICAM-1 (P = 0.02) and vWF (P = 0.009) were greater in SHT and MHT than in normotensives but did not differ between SHT and MHT. We observed a significant positive correlation between blood pressure and soluble activation markers at lower blood pressures (normotensives and MHT considered together) that was not present in SHT. CONCLUSIONS: Even mild elevation of blood pressure may be sufficient to activate the expression of adhesion molecules. Mechanisms other than the endothelial expression of adhesion molecules may be important in mediating the accelerated target organ injury produced by SHT in humans. Concentrations of soluble adhesion molecules and vWF may depend more strongly upon factors in the hypertensive microenvironment other than the absolute level of blood pressure.

Adult↗

PubMed2002

Comparative effects on dynamic renal potassium excretion of ACE inhibition versus angiotensin receptor blockade in hypertensive patients with type II diabetes mellitus.

Both ACE inhibitors (ACEI) and angiotensin receptor blockers (ARB) are renoprotective beyond their effects on blood pressure (BP), but their widespread use is limited by their tendency to provoke hyperkalemia. The comparative effects of ACEI and ARB on potassium handling have not been investigated. The objective of this study was to determine whether there are differences in dynamic renal potassium handling between ACEI and ARB in response to an oral potassium challenge. This was a randomized crossover study of candesartan versus lisinopril titrated to control BP followed by an inpatient study of renal potassium handling in 24 hypertensive patients with type II diabetes mellitus (DMII) and preserved renal function. Following an oral potassium challenge (0.75 mmol/kg), differences in hourly serum K (mmol/L), rate of urinary potassium excretion (UkV, micromol/min), and fractional excretion of potassium (FEK) were assessed by repeated-measures ANOVA. Hourly UkV(p = .45) and FEK (p = .19) were similar for candesartan and lisinopril, although FEK at 2 hours for candesartan tended to exceed that for lisinopril (.34 [.04] vs. .26 [.03]) and approached significance (p = .096). UkVfor candesartan at hour 2 was 177 (26) and 121 (21) for lisinopril and also approached significance (p = .10). Serial serum potassium did not differ (p = .70). No statistical differences were discovered in renal potassium handling between candesartan and lisinopril in patients with DMII and preserved renal function. Whether there are differences between the drug classes in renal impairment remains to be determined.

Administration, Oral↗

PubMedDate not supplied

Diagnostic and interventional nephrology.

The fragmented care of nephrology patients that results from referral to a radiologist for renal ultrasound (US) and biopsy, a surgeon for dialysis access placement, and an interventional radiologist for dialysis catheter placement and vascular access procedures often leads to delays in the treatment of these patients. Many specialists perform and interpret sonograms particular to their specialty rather than relying on technicians for performance and radiologists for interpretation, and nephrologists recently have begun to embrace this technology as an aid in the diagnosis and treatment of their patients. By combining an understanding of the pathophysiology of renal disease with the ability to perform clinical correlation and apply the laboratory data, the nephrologist is ideally suited to perform and interpret renal US and US guidance for percutaneous renal biopsies. Additionally, patients requiring peritoneal dialysis (PD) access have traditionally been referred to a general surgeon for catheter placement, which incurs additional delay in therapy and loss of decision-making control by the referring nephrologist. Recent data has emphasized that the peritoneal dialysis access procedure can be performed safely and effectively by a nephrologist trained in PD access procedures. Nephrologists also successfully perform tunneled hemodialysis catheter placement and vascular access procedures on an outpatient basis. The medical needs of patients with renal disease can be safely and efficiently delivered by a nephrologist trained in interventional nephrology (IN). This growing area of expertise will minimize delays, reduce cost, and allow physicians with training in the management of end-stage renal disease (ESRD) patients to be involved in the procedural aspects of their patients' care. An aggressive approach to the development of IN training programs at academic centers is warranted.

Adult↗

PubMedDate not supplied

Radiocontrast-induced nephropathy.

Radiocontrast administration remains the third leading cause of hospital-acquired acute renal failure. Clinically, radiocontrast-induced nephropathy (RIN) is defined as a sudden decline in renal function after radiocontrast administration. Typically, the serum creatinine level begins to increase at 24 to 72 hours after the administration of contrast, peaks at 3 to 5 days, and requires another 3 to 5 days to return to baseline. RIN increases the incidence of life-threatening complications such as sepsis, bleeding, and respiratory failure and increases the cost of medical care by extending the hospital stay. The increased mortality associated with acute renal failure encountered in this scenario calls for a heightened awareness of the diagnosis and prevention of RIN. Whereas individuals with healthy renal function are not generally considered to be at particular risk for RIN, patients with preexisting renal insufficiency and diabetes mellitus are much more likely to experience acute renal failure after contrast administration. In the past, a variety of therapeutic interventions have been used to prevent or attenuate RIN, including saline hydration, diuretics, mannitol, calcium channel antagonists, theophylline, endothelin receptor antagonists, hemodialysis, and dopamine. More recently, studies demonstrate a positive impact of fenoldopam (dopamine-1 receptor, dopamine-1 agonist) and the antioxidant N-acetylcysteine in ameliorating RIN. This article discusses the pathophysiology, risk factors, and prevention of RIN.

Acute Kidney Injury↗

PubMedDate not supplied

University of Miami Division of Clinical Pharmacology Therapeutic Rounds: medications used to treat anorexia in the frail elderly.

Weight loss and anorexia are common problems that are associated with increased morbidity and mortality in the growing frail elderly population. Orexigenic agents are often prescribed in an attempt to improve appetite and lean muscle mass. Much of the data regarding their benefit comes from studies involving younger patients with illnesses such as acquired immunodeficiency syndrome or cancer. This article reviews the use and potential adverse events associated with these medications in frail elderly patients. This article also discusses the effects of the different antidepressants and antipsychotics on weight gain and appetite.

Aged↗

PubMedDate not supplied

Randomized, placebo-controlled trial of the effects of drospirenone-estradiol on blood pressure and potassium balance in hypertensive postmenopausal women receiving hydrochlorothiazide.

OBJECTIVE: Drospirenone (DRSP), a spironolactone analog with aldosterone antagonist activity, is a novel progestogen developed for use as hormone therapy in postmenopausal women in combination with 17beta-estradiol (E2). DRSP/E2 lowers blood pressure when used alone in hypertensive postmenopausal women or when administered concomitantly with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers. DRSP/E2 has not been studied in combination with the widely prescribed hydrochlorothiazide (HCTZ). We investigated the effects of 3 mg DRSP/1 mg E2 versus placebo on blood pressure and potassium balance when added to existing therapy with 25 mg HCTZ in postmenopausal women with established stage I hypertension. DESIGN: This was a single-center, double-blind, randomized, placebo-controlled, two-treatment, two 4-week treatment period crossover study in 36 postmenopausal women with stage I hypertension maintained on 25 mg HCTZ. The endpoint was a change from baseline in systolic and diastolic blood pressures by 24-hour ambulatory blood pressure monitoring. Safety monitoring included serum potassium (mEq/L) and adverse events. RESULTS: Mean systolic and diastolic blood pressures by 24-hour ambulatory blood pressure monitoring were reduced significantly, by -7.2 and -4.5 mm Hg, respectively, with DRSP/E2 as compared with placebo. The decrease in potassium with HCTZ was 0.2 mEq/L less with DRSP/E2 than placebo, suggesting a potassium-sparing effect. The most frequently observed adverse events with DRSP/E2 were vaginal bleeding and breast tenderness, which were attributable to the hormone therapy. CONCLUSIONS: DRSP/E2 substantially lowers systolic and diastolic blood pressure when added to existing antihypertensive therapy with HCTZ in hypertensive postmenopausal women. In addition, DRSP/E2 has a potassium-sparing effect that counteracts HCTZ-induced potassium loss.

Aged↗

PubMedDate not supplied

Current trials of interventions to prevent radiocontrast-induced nephropathy.

Radiocontrast administration is a common cause of hospital-acquired acute renal failure. It is associated with significant in-hospital and long-term morbidity and mortality and increases the costs of medical care by at least extending the hospital stay. A variety of therapeutic interventions, including saline hydration, diuretics, mannitol, calcium channel antagonists, theophylline, endothelin receptor antagonists, and dopamine, have been employed to prevent radiocontrast-induced acute renal failure. Recent advances have examined the impact of fenoldopam (dopamine-1 receptor agonist), N-acetylcysteine (antioxidant), iso-osmolar contrast agents, hemodialysis, and hemofiltration on ameliorating radiocontrast-induced acute renal failure. Although hydration with half-normal saline had remained the gold standard for the prevention of radiocontrast-induced nephropathy, recent data have revealed the superiority of hydration with normal saline over half-normal saline. This review focuses on the most recent studies of interventions to ameliorate radiocontrast-induced acute renal failure and provides a critical analysis of some of the recent studies conducted to prevent radiocontrast-induced nephropathy.

Acetylcysteine↗