Leaf water stable isotopes and water transport outside the xylem.

How water moves through leaves, and where the phase change from liquid to vapour occurs within leaves, remain largely mysterious. Some time ago, we suggested that the stable isotope composition of leaf water may contain information on transport pathways beyond the xylem, through differences in the development of gradients in enrichment within the various pathways. Subsequent testing of this suggestion provided ambiguous results and even questioned the existence of gradients in enrichment within the mesophyll. In this review, we bring together recent theoretical developments in understanding leaf water transport pathways and stable isotope theory to map a path for future work into understanding pathways of water transport and leaf water stable isotope composition. We emphasize the need for a spatially, anatomically and isotopically explicit model of leaf water transport.

A single-substrate model to interpret intra-annual stable isotope signals in tree-ring cellulose.

The carbon and oxygen stable isotope composition of wood cellulose (delta(13)C(cellulose) and delta(18)O(cellulose), respectively) reveal well-defined seasonal variations that contain valuable records of past climate, leaf gas exchange and carbon allocation dynamics within the trees. Here, we present a single-substrate model for wood growth to interpret seasonal isotopic signals collected in an even-aged maritime pine plantation growing in South-west France, where climate, soil and flux variables were also monitored. Observed seasonal patterns in delta(13)C(cellulose) and delta(18)O(cellulose) were different between years and individuals, and mostly captured by the model, suggesting that the single-substrate hypothesis is a good approximation for tree ring studies on Pinus pinaster, at least for the environmental conditions covered by this study. A sensitivity analysis revealed that the model was mostly affected by five isotopic discrimination factors and two leaf gas-exchange parameters. Modelled early wood signals were also very sensitive to the date when cell wall thickening begins (t(wt)). Our model could therefore be used to reconstruct t(wt) time series and improve our understanding of how climate influences this key parameter of xylogenesis.

Components of ecosystem evaporation in a temperate coniferous rainforest, with canopy transpiration scaled using sapwood density.

Here we develop and test a method to scale sap velocity measurements from individual trees to canopy transpiration (E(c)) in a low-productivity, old-growth rainforest dominated by the conifer Dacrydium cupressinum. Further, E(c) as a component of the ecosystem water balance is quantified in relation to forest floor evaporation rates and measurements of ecosystem evaporation using eddy covariance (E(eco)) in conditions when the canopy was dry and partly wet. Thermal dissipation probes were used to measure sap velocity of individual trees, and scaled to transpiration at the canopy level by dividing trees into classes based on sapwood density and canopy position (sheltered or exposed). When compared with ecosystem eddy covariance measurements, E(c) accounted for 51% of E(eco) on dry days, and 22% of E(eco) on wet days. Low transpiration rates, and significant contributions to E(eco) from wet canopy evaporation and understorey transpiration (35%) and forest floor evaporation (25%), were attributable to the unique characteristics of the forest: in particular, high rainfall, low leaf area index, low stomatal conductance and low productivity associated with severe nutrient limitation.

Drug therapy and prevalence of erectile dysfunction in the Massachusetts Male Aging Study cohort.

STUDY OBJECTIVE: To examine the association of commonly used drugs with erectile dysfunction (ED) at two time points. DESIGN: Population-based, cross-sectional, survey analysis. PARTICIPANTS: Randomly selected cohort of men in the Massachusetts Male Aging Study (MMAS) that included 1476 men for the baseline (1987-1989) and 922 for the follow-up (1995-1997) analyses. INTERVENTION: Crude associations between specific drug categories were examined with chi2 statistics. Logistic regression analysis was used to separate the effect of drugs from the influence of heart disease, hypertension, untreated diabetes, or depressive symptoms. MEASUREMENTS AND MAIN RESULTS: In the MMAS, medical history, current drug use, and erectile function status were ascertained with in-home interviews. In unadjusted analyses, thiazide and nonthiazide diuretics, beta-blockers, calcium channel blockers, angiotensin-converting enzyme inhibitors, benzodiazepines, digitalis, nitrates, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, and histamine2 receptor antagonists were associated with prevalent ED. Adjustment for comorbidities and health behaviors attenuated these associations, with only nonthiazide diuretics and benzodiazepines remaining statistically significant. CONCLUSION: Several common drugs may increase prevalence of ED; however, additional data from larger populations are needed to determine whether these associations are independent of underlying health conditions and to explore the effects of dosage and duration of use.

Pharmacotherapy of systolic heart failure: emphasis on mortality outcomes.

Mortality outcomes in clinical trials have become the foundation for the evidence-based management of patients with systolic heart failure. This review was intended to give the clinician a better understanding of newer pharmacological strategies in this patient population.

Pharmacology and pharmacotherapy of cardiovascular drugs in patients with chronic renal disease.

Cardiovascular disease is a common comorbidity and a major cause of mortality in patients with chronic renal disease. Drug regimens in patients with cardiovascular disease are frequently complex and can be significantly affected by alterations in renal function. In addition, several cardiovascular drugs directly affect renal function and the management of patients with renal disease. This article reviews the impact of renal disease on the pharmacokinetics of cardiovascular drugs and identifies clinically important interactions between these and other drugs commonly used in the management of chronic renal disease. Several classes of cardiovascular drugs are also discussed in relationship to their differential effects on the management and progression of renal disease.

Variation in the oxygen isotope ratio of phloem sap sucrose from castor bean. Evidence in support of the Péclet effect.

Theory suggests that the level of enrichment of (18)O above source water in plant organic material (Delta) may provide an integrative indicator of control of water loss. However, there are still gaps in our understanding of the processes affecting Delta. One such gap is the observed discrepancy between modeled enrichment of water at the sites of evaporation within the leaf and measured enrichment of the leaf water as a whole (Delta(L)). Farquhar and Lloyd (1993) suggested that this may be caused by a Péclet effect. It is also unclear whether organic material formed in the leaf reflects enrichment of water at the sites of evaporation within the leaf or Delta(L). To investigate this question castor bean (Ricinus communis L.) leaves, still attached to the plant, were sealed into a controlled-environment gas exchange chamber and subjected to a step change in leaf-to-air vapor pressure difference. Sucrose was collected from a cut on the petiole of the leaf in the chamber under equilibrium conditions and every hour for 6 h after the change in leaf-to-air vapor pressure difference. Oxygen isotope composition of sucrose in the phloem sap (Delta(suc)) reflected modeled Delta(L). A model is presented describing Delta(suc) at isotopic steady state, and accounts for 96% of variation in measured Delta(suc). The data strongly support the Péclet effect theory.

Antiischemic therapy in patients with coronary heart disease living in long-term care. Systematic Assessment of Geriatric Drug Use by Epidemiology (SAGE) Group.

We evaluated antiischemic therapy in elderly nursing home residents with a diagnosis of coronary heart disease (CHD) using a population-based data base with over 300,000 residents (1992-1995) of all Medicare/Medicaid-certified nursing homes of five states. We identified 72,263 patients age 65 years or older with a diagnosis of CHD. We examined data collected with the federally mandated Minimum Data Set, drug information, and Medicare hospital claims. Antiischemics were defined as beta-adrenergic blockers, long-term nitrates, and calcium channel blockers. We determined factors associated with use of the drugs by logistic regression. Antiischemic therapy was inversely related to age and cognitive and physical functioning, but positively associated with recent hospitalization and concomitant cardiovascular diseases. beta-Adrenergic blockers were least likely to be administered regardless of age, gender, or cognitive or physical function. We conclude that antiischemic therapy in nursing home residents may not be optimal.

Correlates of oral contraceptive use in two New England communities: 1981-1993.

This study compared the sociodemographic and cardiovascular correlates of oral contraceptive users and nonusers between 1981 and 1993. We also sought to determine changes in the prevalence of oral contraceptive use among older premenopausal women. Using data from six biennial cross-sectional household surveys in a population-based sample of two New England communities, 5239 women between ages 18 and 45 years were identified. Women using oral contraceptives were 5 years younger and better educated than nonusers, and users more frequently reported a per capita income above the median for the survey population than nonusers. Users were more likely to report smoking and have a lower body mass index than nonusers. Little use of oral contraceptives was detected among women ages 40-45 years despite changes in FDA recommendations about their use and increasing evidence of their noncontraceptive benefits in healthy older nonsmoking women.

Is a history of depressive symptoms associated with an increased risk of infertility in women?

Researchers have reported an association between self-reported antidepressant use and increased risk of ovulatory infertility but could not control for confounding by the drug indication. We evaluated the role of depressive symptoms in the development of infertility. We recontacted a population-based sample of Pawtucket Heart Health Program (PHHP) health survey respondents to perform this case-control study. Self-reported infertility was defined as an inability to conceive after 12 months of unprotected intercourse. Controls were women who reported at least one pregnancy. The index age for infertile women was the age at which they first experienced fertility problems, and for the fertile women it was the age of their first pregnancy. History of depressive symptoms was based on self-report before the index age. Women with a history of depressive symptoms were nearly twice as likely to report infertility relative to women without a history of depressive symptoms before the index age after controlling for potential confounders (90% confidence interval: 0.9-3.2). Our data suggest that depressive symptoms as well as the drugs used to treat these conditions may play an important role in the pathogenesis of infertility. The association between depressive symptoms and infertility should be explored further.

Cardiovascular risk profiles of oral contraceptive users and nonusers: a population-based study.

BACKGROUND: The purpose of this population-based study was to evaluate whether women taking oral contraceptive products (OCPs) have more favorable cardiovascular disease (CVD) risk profiles than women not taking OCPs. METHODS: Data including sociodemographic variables and CVD risk factors from 5,239 women of reproductive age were gathered in six cross-sectional household surveys. Differences in CVD risk factor profiles between OCP users and nonusers were compared using logistic regression. younger users and older users were compared with nonusers of the same age groups. RESULTS: Women using OCPs (n = 807) were younger and had higher socioeconomic status than nonusers (n = 4,432). More users than nonusers were current smokers (43.1% vs 36.6%, P = 0.0011), had a total serum cholesterol level > or = 240 mg/dl (12.7% vs 6.0%, P = 0.0001), and tended to rate themselves to be at low risk for CVD (48.3% vs 45.5%, P = 0.17). Fewer OCP users than nonusers had an HDL cholesterol level < or = 35 mg/dl (4.0% vs 6.9%, P = 0.0039). CONCLUSIONS: Although they tended to perceive themselves to be at low risk, women taking OCPs in this study had worse CVD risk profiles than women not reporting hormonal contraception and are candidates for cardiovascular risk reduction strategies.

Prior and current health characteristics of postmenopausal estrogen replacement therapy users compared with nonusers.

OBJECTIVE: Our purpose was to investigate whether selection of healthy women for postmenopausal estrogen therapy may confound observational studies of estrogen use and cardiovascular disease risk. STUDY DESIGN: Data were obtained from baseline (1981 to 1984) and follow-up (1990 to 1992) health surveys of two cohorts randomly selected from communities in southeastern New England. At follow-up postmenopausal women > or = 40 years old were categorized as current users (n = 70) or nonusers (n = 772) of noncontraceptive estrogen. Users and nonusers were compared on both prior characteristics from the baseline surveys and current characteristics measured at follow-up by use of analysis of covariance. RESULTS: Prior levels of total and high-density lipoprotein cholesterol, body mass index, and blood pressure were similar for estrogen users and nonusers. Estrogen users were less likely to have smoked and more likely to have had their cholesterol checked and to exercise regularly. These differences were more pronounced for current characteristics than for baseline characteristics. CONCLUSIONS: Selection of healthy women for treatment may not fully explain the apparent protective effect of estrogen replacement on cardiovascular risk. However, more healthy profiles among estrogen users may inflate the apparent benefit of treatment in observational studies.

Is the use of psychotropic drugs associated with increased risk of ischemic heart disease?

Earlier reports of associations between panic disorder, depression, and ischemic heart disease have not evaluated the role of the drugs used to treat these conditions. As part of a larger study on reducing cardiovascular disease in an entire community, we estimated the association between psychotropic drugs and ischemic heart disease in a large community-based population using a cohort study design. We defined exposure as current use of psychotropic medications at the time of the health interview. We determined ischemic heart disease by International Classification of Diseases, 9th revision, Clinical Modification, codes and by an epidemiologic algorithm using clinical diagnostic criteria. An elevated risk for clinically significant ischemic cardiac events was moderately associated with benzodiazepine use [relative risk (RR) = 2.0; 90% confidence interval (CI) = 1.1-3.9] and strongly associated with antidepressant use (RR = 5.7; 90% CI = 2.6-12.8), although the latter estimate was based on only six antidepressant users who had an ischemic event.

Predictors of future antihypertensive use in patients with mildly elevated blood pressure.

We prospectively identified predictors of future antihypertensive use in untreated persons age 18-65 years who had elevated diastolic blood pressures of 90-104 mm Hg or systolic blood pressures of at least 140 mm Hg. Data were derived from two independent cohorts completing household surveys conducted in 1981-1984 and 8 years later, as part of the Pawtucket Heart Health Program. Demographics, self-reported health behaviors and beliefs, and physiologic measurements were obtained. Drug use was determined through structured interviews. Analysis of covariance and logistic regression were performed. In the 492 subjects, independent baseline predictors of future antihypertensive use (p < 0.05) included female gender, older age, diastolic blood pressure elevation, self-perceived high blood pressure, and self-reported salt limitation. Antihypertensive use for previously untreated mild hypertension is diverse. Older women with diastolic elevations who are health conscious are most likely to be treated.

Is antidepressant use changing? Prevalence and clinical correlates in two New England communities.

We attempted to determine whether the prevalence of antidepressant use had increased in population-based samples between 1981 and 1993, and compared the characteristics of antidepressant users and nonusers. Data were derived from six biennial, random sample, cross-sectional household surveys conducted between 1981 and 1993 in two southeastern New England communities. For each survey, point prevalence estimates were determined for the major antidepressant categories. Antidepressant users were most likely to be women, slightly older, and less likely to be employed than nonusers (p < 0.0001). Comorbid conditions and concurrent drug therapy were present more frequently among users. The overall prevalence of antidepressant use per 1000 population increased from 7.8 (95% confidence interval 4.3, 11.3) in 1981-1982 to 31.4 (95% CI 23.9, 38.9) in 1992-1993, especially among women and respondents between ages 40 and 59 years.

Comparison of dobutamine and exercise using technetium-99m sestamibi imaging for the evaluation of coronary artery disease.

Studies using dobutamine thallium-201 myocardial perfusion imaging have suggested a high sensitivity and specificity for the detection of coronary artery disease. However, few data are available comparing dobutamine with exercise stress for the detection and localization of perfusion defects. This study compared the effects of dobutamine and exercise stress using technetium-99m sestamibi single-photon emission computed tomographic imaging in the same patients in a prospective crossover trial. Twenty-four patients with a high likelihood of coronary artery disease underwent tomographic myocardial imaging at rest, after symptom-limited treadmill exercise, and after intravenous dobutamine (maximum 30 micrograms/kg/min). Tomograms of the left ventricle were divided into 20 segments and were interpreted without knowledge of patient identity or stress protocol. Dobutamine was well tolerated by all patients. Segment-by-segment concordance between exercise and dobutamine images was highly significant (kappa = 0.56, p < 0.0001). Global first-order agreement (normal vs abnormal) between exercise and dobutamine studies was 96% (kappa = 0.65, p = 0.02); global second-order agreement (normal vs fixed vs ischemic defect) was 88% (kappa = 0.45, p = 0.02). Regional first- and second-order agreement were 96 and 93%, respectively (p < 0.001 for both). Twenty patients underwent coronary angiography. Comparisons between exercise and angiography and between dobutamine and angiography were similar for both global agreement (95 vs 100%, p = NS) and regional agreement (77 vs 72%, p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Pretreatment with theophylline does not affect adenosine-induced thallium-201 myocardial imaging.

This study was designed to evaluate the effects of intravenous theophylline given before intravenous adenosine for thallium-201 imaging. Sixteen patients with known reversible thallium-201 defects were randomized to a double-blind crossover study of a 45-minute infusion of placebo or theophylline (given as the ethylenediamine salt, aminophylline, mean concentration 16.1 mg/L) before adenosine thallium-201 imaging. Adenosine was infused for 6 minutes at a rate of 140 micrograms/kg/min. Thallium-201 (2.5 to 3.0 mCi) was administered after 3 minutes of infusion. Blood pressure, heart rate, symptoms, and the electrocardiogram were monitored continuously. Planar thallium-201 imaging was obtained in three standard views and was interpreted using blinded segmental analysis and computerized quantitation. Systolic and diastolic blood pressure at baseline and during adenosine administration were similar following treatment with theophylline and placebo. The increase in heart rate observed during adenosine infusion was significantly reduced by theophylline pretreatment. Adenosine-induced symptoms (both cardiac and noncardiac) as well as ischemic electrocardiographic changes were significantly reduced after theophylline infusion (p < 0.05). In one patient, Mobitz type II heart block seen during adenosine infusion following placebo was absent with theophylline pretreatment. The size of adenosine-induced thallium-201 defects was unchanged by theophylline infusion using either segmental analysis (8 +/- 4 vs 9 +/- 5) or a computerized score (47 +/- 27 vs 45 +/- 21). Despite reduction in both symptoms and ischemic electrocardiographic changes, theophylline does not alter thallium-201 imaging following intravenous adenosine infusion.