Intensive Glucose Control in Patients with Type 2 Diabetes - 15-Year Follow-up

BACKGROUND

We previously reported that a median of 5.6 years of intensive as compared with standard glucose lowering in 1791 military veterans with type 2 diabetes resulted in a risk of major cardiovascular events that was significantly lower (by 17%) after a total of 10 years of combined intervention and observational follow-up. We now report the full 15-year follow-up.

METHODS

We observationally followed enrolled participants (complete cohort) after the conclusion of the original clinical trial by using central databases to identify cardiovascular events, hospitalizations, and deaths. Participants were asked whether they would be willing to provide additional data by means of surveys and chart reviews (survey cohort). The prespecified primary outcome was a composite of major cardiovascular events, including nonfatal myocardial infarction, nonfatal stroke, new or worsening congestive heart failure, amputation for ischemic gangrene, and death from cardiovascular causes. Death from any cause was a prespecified secondary outcome.

RESULTS

There were 1655 participants in the complete cohort and 1391 in the survey cohort. During the trial (which originally enrolled 1791 participants), the separation of the glycated hemoglobin curves between the intensive-therapy group (892 participants) and the standard-therapy group (899 participants) averaged 1.5 percentage points, and this difference declined to 0.2 to 0.3 percentage points by 3 years after the trial ended. Over a period of 15 years of follow-up (active treatment plus post-trial observation), the risks of major cardiovascular events or death were not lower in the intensive-therapy group than in the standard-therapy group (hazard ratio for primary outcome, 0.91; 95% confidence interval [CI], 0.78 to 1.06; P = 0.23; hazard ratio for death, 1.02; 95% CI, 0.88 to 1.18). The risk of major cardiovascular disease outcomes was reduced, however, during an extended interval of separation of the glycated hemoglobin curves (hazard ratio, 0.83; 95% CI, 0.70 to 0.99), but this benefit did not continue after equalization of the glycated hemoglobin levels (hazard ratio, 1.26; 95% CI, 0.90 to 1.75).

CONCLUSIONS

Participants with type 2 diabetes who had been randomly assigned to intensive glucose control for 5.6 years had a lower risk of cardiovascular events than those who received standard therapy only during the prolonged period in which the glycated hemoglobin curves were separated. There was no evidence of a legacy effect or a mortality benefit with intensive glucose control. (Funded by the VA Cooperative Studies Program; VADT ClinicalTrials.gov number, NCT00032487.).

A comparison of neuropsychiatric adverse events during early treatment with varenicline or a nicotine patch

AIMS

We compared the risk of mental health episodes requiring hospitalization (primary aim) or out-patient clinic visits (secondary aim) associated with varenicline versus the nicotine patch (NP) in an era prior to psychiatric boxed warnings.

DESIGN

Retrospective cohort.

SETTING

Department of Veterans Affairs (VA), USA.

PARTICIPANTS

VA patients with or without psychiatric comorbidities and a new prescription for varenicline (15 255) were propensity score-matched (1 : 2) to new users of NP (123 054) between 1 May 2006 and 30 September 2007, resulting in 11 774 and 23 548 patients in the varenicline and NP groups, respectively.

MEASUREMENTS

The primary outcomes were hospitalizations with a primary discharge diagnosis of a range of mental health disorders: depression, schizophrenia, bipolar disorder, suicide attempt, post-traumatic stress disorder, other psychosis and drug-induced mental disorders. Secondary outcomes were out-patient clinic visits with a primary diagnosis of the above list of mental health disorders.

FINDINGS

Background characteristics of the treatment groups were similar after matching. There was no statistically significant difference in risk of hospitalization for any of the studied mental health disorders with varenicline compared with NP. Among secondary outcomes there was an increased risk of out-patient clinic visits for schizophrenia among patients who received varenicline [hazard ratio (HR) = 1.27; 95% confidence interval (CI) = 1.07, 1.51], this increase being evident only in those with a pre-existing mental health disorder.

CONCLUSION

In US VA patients studied prior to the boxed warning being implemented, use of varenicline for smoking cessation was not associated with a detectable increase compared with nicotine patches in hospitalization for any mental health outcomes. There was an increased rate of out-patient attendances with a primary diagnosis of schizophrenia amounting to five per 100 person years of treatment. This increase was found only in patients with a pre-existing mental health disorder.

Follow-up of glycemic control and cardiovascular outcomes in type 2 diabetes

BACKGROUND

The Veterans Affairs Diabetes Trial previously showed that intensive glucose lowering, as compared with standard therapy, did not significantly reduce the rate of major cardiovascular events among 1791 military veterans (median follow-up, 5.6 years). We report the extended follow-up of the study participants.

METHODS

After the conclusion of the clinical trial, we followed participants, using central databases to identify procedures, hospitalizations, and deaths (complete cohort, with follow-up data for 92.4% of participants). Most participants agreed to additional data collection by means of annual surveys and periodic chart reviews (survey cohort, with 77.7% follow-up). The primary outcome was the time to the first major cardiovascular event (heart attack, stroke, new or worsening congestive heart failure, amputation for ischemic gangrene, or cardiovascular-related death). Secondary outcomes were cardiovascular mortality and all-cause mortality.

RESULTS

The difference in glycated hemoglobin levels between the intensive-therapy group and the standard-therapy group averaged 1.5 percentage points during the trial (median level, 6.9% vs. 8.4%) and declined to 0.2 to 0.3 percentage points by 3 years after the trial ended. Over a median follow-up of 9.8 years, the intensive-therapy group had a significantly lower risk of the primary outcome than did the standard-therapy group (hazard ratio, 0.83; 95% confidence interval [CI], 0.70 to 0.99; P=0.04), with an absolute reduction in risk of 8.6 major cardiovascular events per 1000 person-years, but did not have reduced cardiovascular mortality (hazard ratio, 0.88; 95% CI, 0.64 to 1.20; P=0.42). No reduction in total mortality was evident (hazard ratio in the intensive-therapy group, 1.05; 95% CI, 0.89 to 1.25; P=0.54; median follow-up, 11.8 years).

CONCLUSIONS

After nearly 10 years of follow-up, patients with type 2 diabetes who had been randomly assigned to intensive glucose control for 5.6 years had 8.6 fewer major cardiovascular events per 1000 person-years than those assigned to standard therapy, but no improvement was seen in the rate of overall survival. (Funded by the VA Cooperative Studies Program and others; VADT ClinicalTrials.gov number, NCT00032487.).

Engineering practice variation through provider agreement: a cluster-randomized feasibility trial

Purpose

Minimal-risk randomized trials that can be embedded in practice could facilitate learning health-care systems. A cluster-randomized design was proposed to compare treatment strategies by assigning clusters (eg, providers) to “favor” a particular drug, with providers retaining autonomy for specific patients. Patient informed consent might be waived, broadening inclusion. However, it is not known if providers will adhere to the assignment or whether institutional review boards will waive consent. We evaluated the feasibility of this trial design.

Subjects and methods

Agreeable providers were randomized to “favor” either hydrochlorothiazide or chlorthalidone when starting patients on thiazide-type therapy for hypertension. The assignment applied when the provider had already decided to start a thiazide, and providers could deviate from the strategy as needed. Prescriptions were aggregated to produce a provider strategy-adherence rate.

Results

All four institutional review boards waived documentation of patient consent. Providers (n=18) followed their assigned strategy for most of their new thiazide prescriptions (n=138 patients). In the “favor hydrochlorothiazide” group, there was 99% adherence to that strategy. In the “favor chlorthalidone” group, chlorthalidone comprised 77% of new thiazide starts, up from 1% in the pre-study period. When the assigned strategy was followed, dosing in the recommended range was 48% for hydrochlorothiazide (25–50 mg/day) and 100% for chlorthalidone (12.5–25.0 mg/day). Providers were motivated to participate by a desire to contribute to a comparative effectiveness study. A study promotional mug, provider information letter, and interactions with the site investigator were identified as most helpful in reminding providers of their study drug strategy.

Conclusion

Providers prescribed according to an assigned drug-choice strategy most of the time for the purpose of a comparative effectiveness study. This simple design could facilitate research participation and behavior change in non-research clinicians. Waiver of patient consent can broaden the representation of patients, providers, and settings.

Abstract 137: Anticoagulation clinic provider’s perspective on management of patients on target specific oral anticoagulants: insights from the Veterans Affairs Health Care System

Background: Patients on target specific anticoagulants (TSOACs) such as dabigatran do not require routine laboratory testing and dose adjustment. In the Veterans Health Administration (VHA), anticoagulation clinics (ACCs) may elect to follow and manage patients on TSOACs, but whether it is needed or the optimal duration of follow-up is unknown. Our objective was to assess the perspective of anticoagulation clinic providers on follow-up care for dabigatran patients and to identify site-level practices associated with improved adherence to dabigatran.

Methods: We ascertained ACC providers’ perspectives through semi-structured interviews by a single, trained internist. Purposive sampling was utilized to recruit senior ACC providers or supervisors at VHA sites with over 20 patients on dabigatran. We stratified sites into high and low performing sites based on whether sites had ≥ 75% of their patients adherent, based on a proportion-of-days-covered calculation. Data from the interviews was analyzed by 2 reviewers in an iterative process to identify recurrent and unifying themes. Constant comparative method of qualitative data analysis was used to identify best practices across various sites.

Results: We interviewed ACC providers from 39 sites - including 18 providers at 16 high-performing sites and 25 providers at 23 low-performing sites. Follow-up practices for dabigatran varied across sites, with 6 sites not providing any follow-up, 14 sites following-up patients for less than 3 months, 9 sites following-up patients for 6 months, and 10 sites following-up patients indefinitely. During these follow-up visits, patients were contacted at regular intervals, mostly via telephone, by ACC providers to provide education, assess side-effects and adherence. Key strategies implemented at high-performing sites compared to low-performing sites included (1) examining adherence to other twice daily medications prior to approving dabigatran (2) education of patients by ACC providers prior to dabigatran initiation (3) continued telephone follow up by ACC staff despite no need for INR checks. Over a third of ACC providers expressed concerns regarding patient adherence to dabigatran. Most common reasons for this concern included its special storage requirements and high incidence of gastrointestinal side effects leading to high discontinuation rates.

Conclusion: Dedicated follow-up of patients on dabigatran is associated with improved adherence. A multi-disciplinary approach involving anti-coagulation clinic providers to provide education and follow-up may be beneficial in management of TSOACs. Future work should compare the apparent benefit of this strategy with its non-trivial cost.

Association of PAI-1 and fibrinogen with diabetic retinopathy in the Veterans Affairs Diabetes Trial (VADT)

OBJECTIVE

To test the hypothesis that high levels of plasminogen-activating inhibitor (PAI)-1 and fibrinogen at baseline were associated with the onset or progression of diabetic retinopathy (DR) during the Veterans Affairs Diabetes Trial (VADT).

RESEARCH DESIGN AND METHODS

The VADT was an open-label, prospective, randomized controlled trial to test the effect of standard glycemic control (STD) compared with intensive control (INT) on cardiovascular events in patients with advanced type 2 diabetes mellitus (T2DM). Diabetic retinopathy (DR) outcomes were also collected. Incidence and progression of DR were assessed by grading seven-field stereoscopic fundus photographs at baseline and 5 years later taken in 858 of a total of 1,791 participants who completed both eye examinations.

RESULTS

Assignment to INT was not independently associated with decreased risk of onset of DR. However, after adjustment for multiple covariates, baseline level of PAI-1 was an independent risk factor for the onset of DR. The risk for incidence of DR increased by 12% for each 10 ng/dL increase in baseline PAI-1 concentration (odds ratio [OR] 1.012 [95% CI 1.00-1.024], P = 0.042). Assignment to INT was not independently associated with decreased risk of progression of DR. However, there was an interaction between glycemic treatment assignment and fibrinogen level at baseline. INT was associated with decreased progression of retinopathy in those with fibrinogen <296 mg/dL (OR 0.55 [95% CI 0.31-1.00], P = 0.03).

CONCLUSIONS

The results require confirmation but are consistent with greater hypercoagulabilty and inflammation, as measured by higher levels of PAI-1 and fibrinogen, being related to DR and responsiveness to INT.

Research leadership and investigators: gender distribution in the federal government

BACKGROUND

The National Academies reported in Beyond Bias and Barriers: Fulfilling the Potential of Women in Academic Science and Engineering (2006) that "women are very likely to face discrimination." In academic medicine, gender distribution is becoming more balanced. In the federal government, women also have made progress, doubling their representation in professional positions to 44%. The Department of Veterans Affairs (VA) has a research program and a mission to train health care professionals; however, its gender distribution has not been described.

METHODS

We conducted a descriptive study using public data for positions in the VA, National Institutes of Health (NIH), and Agency for Healthcare Research and Quality (AHRQ). We followed with a case-control analysis of predictors of receipt of grant funding in the VA. Participants were 224 leadership positions and 132 principal investigators.

RESULTS

Women comprised 33% (AHRQ), 27% (NIH), and 0% (VA) of the top research leadership. Across all VA research levels, women comprised 45% to 0%, depending on the service. In the case-control analysis of principal investigators, men had greater odds (odds ratio 8.0) of a Cooperative Studies Program (CSP) trial award. History of first, last, or any authorship on a clinical trial publication in the 10 years before the index trial was only weakly associated with award of a CSP trial. The gender imbalance was not explained by publication history.

CONCLUSIONS

Marked gender disparities were seen in the VA, except in Health Services Research. Organizations must investigate their practices to reveal disparities, investigate underlying factors, and intervene as needed.

[Assessment of the distribution of nucleic acid intercalators in yeast cells by the pseudospectral image analysis]

The intracellular location of nucleic acid intercalators (NAI) in live (not fixed) Saccharomyces cerevisiae cells has been studied using fluorescence microscopy combined with computer pseudospectral image analysis. Three NAI: the anthracycline anticancer drug doxorubicin and the nucleic acid dyes ethidium bromide (E) and 4',6-diamidino-2-phenylindole (DAPI) were used. All three NAI were shown to be localized in nuclei and mitochondria. In contrast to DAPI, which interacted only with DNA, a large fraction of doxorubicin and ethidium bromide apparently bound to mitochondrial membranes. Upon combined application, a competition between these intercalators for binding sites in the nuclear and mitochondrial DNA occurred. It was concluded that this approach may be used in designing new DNA-targeted drugs and in preliminary studies of their interaction with eukaryotic cells.

Effects of the thyromimetic agent diiodothyropropionic acid on body weight, body mass index, and serum lipoproteins: a pilot prospective, randomized, controlled study

CONTEXT

Widespread thyroid hormone actions offer the possibility of developing selective thyromimetic analogs with salutary metabolic properties. Consequently, effects of diiodothyropropionic acid (DITPA) on body weight, serum lipoproteins, and bone metabolism markers were studied in a prospective, controlled, double-blind 24-wk trial, which was primarily designed to assess treatment of stable chronic heart failure.

DESIGN

Eighty-six patients (aged 66 +/- 11 yr, mean +/- sd) were randomized (1:2) to placebo or an escalating DITPA dose (90 to 180, 270, and 360 mg/d) over 8 wk until serum TSH was less than 0.02 mU/liter. Patients were studied at 2, 4, 6, 8, 16, and 24 wk and after 4 wk off study drug. Only 21 DITPA-treated and 27 placebo patients completed the full 24 wk of therapy.

RESULTS

DITPA therapy lowered serum TSH levels and, to a lesser extent, serum T(3) and T(4), but there were no differences in clinical manifestations of thyrotoxicosis or hypothyroidism. Serum total and low-density lipoprotein cholesterol levels both decreased on DITPA; there was a transient decrease in triglycerides and no change in high-density lipoprotein cholesterol. DITPA therapy was associated with significant reduction in body weight, 12.5 lb at 24 wk. Increases in serum osteocalcin, N-telopeptide, and deoxypyridinoline levels were consistent with increased bone turnover on DITPA.

CONCLUSION

This investigation of DITPA actions demonstrated its efficacy in reducing body weight and lowering total and low-density lipoprotein cholesterol levels. However, DITPA's adverse effects at doses used resulted in a high dropout rate and potentially dangerous skeletal actions were observed.

Intensive glucose-lowering therapy reduces cardiovascular disease events in veterans affairs diabetes trial participants with lower calcified coronary atherosclerosis

OBJECTIVE

This study investigated the hypothesis that baseline calcified coronary atherosclerosis may determine cardiovascular disease events in response to intensive glycemic control within the Veterans Affairs Diabetes Trial (VADT).

RESEARCH DESIGN AND METHODS

At baseline, 301 type 2 diabetic participants in the VADT, a randomized trial comparing the effects of intensive versus standard glucose lowering on cardiovascular events, had baseline coronary atherosclerosis assessed by coronary artery calcium (CAC) measured by computed tomography. Participants were followed over the 7.5-year study for development of cardiovascular end points.

RESULTS

During a median follow-up duration of 5.2 years, 89 cardiovascular events occurred. Although intensive glucose-lowering therapy did not significantly reduce cardiovascular events in the substudy cohort as a whole, there was evidence that the response was modified by baseline CAC, as indicated by significant P values for treatment by log(CAC + 1) interaction terms in unadjusted and multivariable-adjusted models (0.01 and 0.03, respectively). Multivariable-adjusted hazard ratios (HRs) for the effect of treatment indicated a progressive diminution of benefit with increasing CAC. Subgroup analyses were also conducted for clinically relevant CAC categories: those above and below an Agatston score of 100. Among those randomized to intensive treatment, for the subgroup with CAC >100, 11 of 62 individuals had events, while only 1 of 52 individuals with CAC < or = 100 had an event. The multivariable HR for intensive treatment for those with CAC >100 was 0.74 (95% CI 0.46-1.20; P = 0.21), while for the subgroup with CAC < or = 100, the corresponding HR was 0.08 (0.008-0.77; P = 0.03), with event rates of 39 and 4 per 1,000 person-years, respectively.

CONCLUSIONS

These data indicate that intensive glucose lowering reduces cardiovascular events in those with less extensive calcified coronary atherosclerosis.

Severe dysglycemia with the fluoroquinolones: a class effect?

BACKGROUND

Although gatifloxacin is no longer available, other fluoroquinolones may significantly interfere with glucose homeostasis. The objective of the present study was to compare the risk of severe hypo- and hyperglycemia in a cohort of patients treated with gatifloxacin, levofloxacin, ciprofloxacin, or azithromycin.

METHODS

This was a retrospective inception cohort study of outpatients with a new prescription for gatifloxacin, levofloxacin, ciprofloxacin, or azithromycin from 1 October 2000 through 30 September 2005 in the Veterans Affairs health care system. For patients who received one of these antibiotics, we identified outcomes of hospitalization with a primary diagnosis of hypo- or hyperglycemia. Multivariable logistic regression was used to determine the odds of hypo- and hyperglycemia with the individual fluoroquinolones versus azithromycin.

RESULTS

The crude incidence rates for severe hypo- and hyperglycemia among those who received gatifloxacin, levofloxacin, ciprofloxacin, and azithromycin were 0.35 and 0.45, 0.19 and 0.18, 0.10 and 0.12, and 0.07 and 0.10 cases per 1000 patients, respectively. Among patients with diabetes, the odds ratios for hypoglycemia compared with azithromycin were 4.3 (95% confidence interval [CI], 2.7-6.6) for gatifloxacin, 2.1 (95% CI, 1.4-3.3) for levofloxacin, and 1.1 (95% CI, 0.6-2.0) for ciprofloxacin. The odds ratios for hyperglycemia were 4.5 (95% CI, 3.0-6.9) for gatifloxacin, 1.8 (95% CI, 1.2-2.7) for levofloxacin, and 1.0 (95% CI, 0.6-1.8) for ciprofloxacin.

CONCLUSIONS

The odds of severe hypo- and hyperglycemia were significantly greater with gatifloxacin and levofloxacin, but not ciprofloxacin, than with azithromycin. Thus, the risk of a clinically relevant dysglycemic event appears to vary among the fluoroquinolones.

DITPA (3,5-Diiodothyropropionic Acid), a thyroid hormone analog to treat heart failure: phase II trial veterans affairs cooperative study

BACKGROUND

In animal studies and a pilot trial in patients with congestive heart failure, the thyroid hormone analog 3,5 diiodothyropropionic acid (DITPA) had beneficial hemodynamic effects.

METHODS AND RESULTS

This was a phase II multicenter, randomized, placebo-controlled, double-blind trial of New York Heart Association class II to IV congestive heart failure patients randomized (2:1) to DITPA or placebo and treated for 6 months. The study enrolled 86 patients (n=57 to DITPA, n=29 to placebo). The primary objective was to assess the effect of DITPA on a composite congestive heart failure end point that classifies patients as improved, worsened, or unchanged based on symptom changes and morbidity/mortality. DITPA was poorly tolerated, which obscured the interpretation of congestive heart failure-specific effects. Fatigue and gastrointestinal complaints, in particular, were more frequent in the DITPA group. DITPA increased cardiac index (by 18%) and decreased systemic vascular resistance (by 11%), serum cholesterol (-20%), low-density lipoprotein cholesterol (-30%), and body weight (-11 lb). Thyroid-stimulating hormone was suppressed in patients given DITPA, which reflects its thyromimetic effect; however, no symptoms or signs of potential hypothyroidism or thyrotoxicosis were seen.

CONCLUSIONS

DITPA improved some hemodynamic and metabolic parameters, but there was no evidence for symptomatic benefit in congestive heart failure.

Glucose control and vascular complications in veterans with type 2 diabetes

BACKGROUND

The effects of intensive glucose control on cardiovascular events in patients with long-standing type 2 diabetes mellitus remain uncertain.

METHODS

We randomly assigned 1791 military veterans (mean age, 60.4 years) who had a suboptimal response to therapy for type 2 diabetes to receive either intensive or standard glucose control. Other cardiovascular risk factors were treated uniformly. The mean number of years since the diagnosis of diabetes was 11.5, and 40% of the patients had already had a cardiovascular event. The goal in the intensive-therapy group was an absolute reduction of 1.5 percentage points in the glycated hemoglobin level, as compared with the standard-therapy group. The primary outcome was the time from randomization to the first occurrence of a major cardiovascular event, a composite of myocardial infarction, stroke, death from cardiovascular causes, congestive heart failure, surgery for vascular disease, inoperable coronary disease, and amputation for ischemic gangrene.

RESULTS

The median follow-up was 5.6 years. Median glycated hemoglobin levels were 8.4% in the standard-therapy group and 6.9% in the intensive-therapy group. The primary outcome occurred in 264 patients in the standard-therapy group and 235 patients in the intensive-therapy group (hazard ratio in the intensive-therapy group, 0.88; 95% confidence interval [CI], 0.74 to 1.05; P=0.14). There was no significant difference between the two groups in any component of the primary outcome or in the rate of death from any cause (hazard ratio, 1.07; 95% CI, 0.81 to 1.42; P=0.62). No differences between the two groups were observed for microvascular complications. The rates of adverse events, predominantly hypoglycemia, were 17.6% in the standard-therapy group and 24.1% in the intensive-therapy group.

CONCLUSIONS

Intensive glucose control in patients with poorly controlled type 2 diabetes had no significant effect on the rates of major cardiovascular events, death, or microvascular complications with the exception of progression of albuminuria (P = 0.01) [added]. (ClinicalTrials.gov number, NCT00032487.)

Baseline achievement of lipid goals and usage of lipid medications in patients with diabetes mellitus (from the Veterans Affairs Diabetes Trial)

The American Diabetes Association has established lipid goals for patients with diabetes. Although diabetic populations historically have poor low-density lipoprotein (LDL) cholesterol goal adherence, little is known about adherence to triglyceride and high-density lipoprotein (HDL) cholesterol goals. To determine the degree of lipid goal attainment among patients with diabetes, and to characterize the patterns of lipid medication use, we evaluated the baseline data from 1,742 enrollees of the national Veterans Affairs Diabetes Trial. Using current American Diabetes Association lipid guidelines, we calculated the proportion of participants achieving a LDL cholesterol level <100 mg/dl, triglyceride level <150 mg/dl, and HDL cholesterol level >40 mg/dl in men (>50 mg/dl in women). We also performed a descriptive analysis of the use of lipid medications in this population. The baseline LDL cholesterol level was 111 +/- 63 mg/dl, triglyceride level was 213 +/- 277 mg/dl, and HDL cholesterol was 36 +/- 10 mg/dl. At enrollment, 44% of veterans met the LDL cholesterol goal, 58% met the triglyceride goal, and 16% met the HDL cholesterol goal, but only 6% met all 3 goals. Of the 1,742 enrollees, 2/3 were receiving lipid therapy, with statins (58%) the most commonly used drug. Combination lipid therapy was used by 11% of enrollees. Although the enrollees of the Veterans Affairs Diabetes Trial demonstrated better adherence to the American Diabetes Association's LDL cholesterol goal than other diabetic populations recently studied, more aggressive and directed lipid medication use is needed to treat the overall lipid profile better.

The association between metabolic control and prevalent macrovascular disease in Type 2 diabetes: the VA Cooperative Study in diabetes

THE PROBLEM

Macrovascular disease (MVD), especially coronary heart disease, is the most common cause of mortality in Type 2 diabetes. We assessed the association between demographic and clinical variables (particularly HbA1c) and prevalent MVD at time of enrollment into the VA Diabetes Trial (VADT), a 7-year randomized trial to determine whether intensive glycemic control will reduce risk of MVD events in older participants with established Type 2 diabetes.

RESEARCH DESIGN AND METHODS

We compared the demographic, treatment, and clinical characteristics of participants with and without known MVD, then assessed the interaction of multiple variables with HbA1c. Logistic regression models evaluated the association between HbA1c quartiles and prevalence of MVD, adjusting for potentially confounding variables.

RESULTS

Several variables were associated with prevalent MVD (age, duration of diabetes, insulin use but not daily dosage, smoking history, hypertension, BMI, Caucasian race, non-Hispanic ethnicity, lower HDL cholesterol, higher triglycerides, lower LDL cholesterol, and statin use). In univariate analysis, there was no association of HbA1c with MVD (mean: 9.4+/-1.46% in those with MVD, 9.5+/-1.58% in those without). Multivariate analyses found little confounding of the lack of association of HbA1c with MVD. Only adjustment for age produced a slight increase in the odds ratio, but only for the highest quartile of HbA1c.

CONCLUSIONS

In this cross-sectional analysis, MVD was associated with a number of clinical and demographic variables but not with HbA1c. Determining whether intensive lowering of HbA1c will reduce the prospective rate of MVD events in this population of older participants with established Type 2 diabetes is the primary objective of our trial.

Control of Cardiovascular Risk Factors in The Veterans Affairs Diabetes Trial in Advanced Type 2 Diabetes

OBJECTIVE

To present a status report on the Veterans Affairs Diabetes Trial (VADT), a multisite long-term study examining the effect of glucose control on cardiovascular (CV) complications in older patients with established, poorly controlled type 2 diabetes.

METHODS

We review the rationale, objectives, and design of the VADT and summarize the baseline data and the results achieved thus far.

RESULTS

The main objective of this 20-site, 1,792-patient study is to ascertain whether intensive glucose control can reduce major CV events in patients with difficult-to-control type 2 diabetes. The study design consists of a standard treatment arm and an intensive treatment arm, with a goal of 1.5% difference in hemoglobin A1c values between the two groups. The trial is now in its fifth year, with completion expected in December 2007. The planned glucose separation has been achieved and maintained to this point. Blood pressure and hemoglobin A1c levels have been reduced from baseline values, and established CV risk factors are within recommended ranges.

CONCLUSION

The current results of the VADT show that excellent control of glucose and CV risk factors can be achieved and maintained in the population studied. The results of these interventions on CV outcomes will ultimately have important implications for the clinical care of older patients with advanced type 2 diabetes.

Design of the cooperative study on glycemic control and complications in diabetes mellitus type 2: Veterans Affairs Diabetes Trial

INTRODUCTION

Long-term glycemic control trials in type 2 diabetes show as the main clinical benefit a difference in retinal photocoagulation (3/1000 in the UK Prospective Diabetes Study [UKPDS]), but no effect on visual acuity or renal failure. No intensive glycemic control trial has yet affected cardiovascular (CV) events, the main cause of morbidity and mortality. By contrast, modest blood pressure reduction has protective effects on visual acuity, renal function, CV events, and mortality. Optimal glycemic control goals are not established in elderly, obese persons with advanced complications, the most common patients in the Veterans Affairs (VA) system. The earlier feasibility trial in such patients (VA-CSDM) suggested potentially worse CV outcomes with lower attained hemoglobin A1c (HbA1c) levels.

OBJECTIVES

The primary objective of the Veterans Affairs Diabetes Trial (VADT) is the assessment of the effect of intensive glycemic treatment on CV events. Other objectives are effects on microangiopathy, quality of life, and cost effectiveness.

RESEARCH DESIGN AND METHODS

The VADT, started in December 2000, is enrolling 1700 men and women previously uncontrolled on insulin or maximum doses of oral agents at 20 VA medical centers. Accrual is 2 years and follow-up is 5-7 years, with visits every 1.5 months. The study has a power of 86% to detect a 21% relative reduction in major CV events (CV death, myocardial infarction [MI], cerebrovascular accident [CVA], congestive heart failure [CHF], revascularization and amputation for ischemia). Subjects are randomized to an intensive arm aiming at normal HbA1c levels or to a standard arm with usual, improved glycemic control. An HbA1c separation of >1.5% is to be maintained (expected 2%). Both arms receive step therapy: glimepiride or metformin plus rosiglitazone and addition of insulin or other oral agents to achieve goals. Strict control of blood pressure and dyslipidemia, daily aspirin, diet, and education are identical in both arms. Plasma fibrinogen, plasminogen-activating inhibitor I (PAI-I), lipids, renal function parameters, and ECG are measured throughout. Stereo retinal photographs are obtained at entry and 5 years, eye examinations yearly, and intervention as needed to prevent visual deterioration. Recruitment is proceeding on schedule: the current mean HbA1c at entry is 9.4+/-1.6% and mean duration of diagnosed diabetes 11+/-8 years.

Two years of intensive glycemic control and left ventricular function in the Veterans Affairs Cooperative Study in Type 2 Diabetes Mellitus (VA CSDM)

OBJECTIVE

The Veterans Affairs Cooperative Study in Type 2 Diabetes Mellitus (VA CSDM) was a multicenter randomized prospective study of 153 male type 2 diabetic patients to assess the ability to sustain clinically significant glycemic separation between intensive and standard treatment arms. A trend toward an excess of combined cardiovascular events in the intensive treatment arm of this trial was reported earlier. The present analysis was done to evaluate the effect of 2 years of intensive glycemic control on the left ventricular (LV) function.

RESEARCH DESIGN AND METHODS

The patients were randomized to intensive step treatment with insulin alone or with sulfonylurea (intensive treatment arm [INT], n = 75) or to standard once-daily insulin injection (standard treatment arm [STD], n = 78) treatment. A total of 136 patients (standard treatment arm [STD], n = 70; INT, n = 66) had radionuclide ventriculography at entry and at 24 months for the assessment of LV function.

RESULTS

There was no difference in the mean LV ejection fraction (at entry: STD 57.1+/-9.51%; INT 58.1+/-8.7%; at 24 months: STD 57.3+/-10.8%, INT 59.5+/-10.7%), peak filling rate (at entry: STD 2.6+/-0.7 end diastolic volume per second, INT 2.4+/-0.8 end diastolic volume per second; at 24 months: STD 2.7+/-1.0 end diastolic volume per second, INT 2.5+/-0.7 end diastolic volume per second), or time to peak filling rate (at entry: STD 195.3+/-69.5 ms, INT 185.6 +/-62.4 ms; at 24 months: STD 182.6+/-64.8 ms, INT 179.2+/-61.2 ms) between the 2 treatment arms. A subgroup analysis of 104 patients (STD, n = 53; INT, n = 51) that omitted individuals with intervening cardiac events/revascularization or a change in cardioactive medications also showed no difference in the LV function at entry and at 24 months between the 2 groups. Abnormal LV ejection fraction at baseline predicted cardiac events (interval between cardiac beats [RR] = 2.5).

CONCLUSIONS

Two years of intensive glycemic control does not affect the LV systolic or diastolic function in patients with type 2 diabetes.

Predicting recovery from acute asthma in an emergency diagnostic and treatment unit

OBJECTIVE

Optimal use of emergency diagnostic and treatment unit (EDTU) resources for treatment of acute asthma should be facilitated by the selection of patients with a high probability of discharge from the EDTU. The study goal was to identify characteristics of the patient or exacerbation that could be used to predict recovery of pulmonary function within 12 hours.

METHODS

Comprehensive cohort design in an urban public hospital. The subjects were 269 patients with moderately severe asthma exacerbations. Data were collected for historical and presenting features and response to treatment over 12 hours. Two outcomes were examined: 1) discharge from the EDTU and 2) achieving 50% predicted peak expiratory flow rate (PEFR) within 12 hours.

RESULTS

The two outcomes showed good concordance. The third-treatment PEFR was found to be predictive of both discharge and reaching 50% predicted PEFR within 12 hours. Since the objective measure of reaching 50% predicted PEFR is more readily defined and thus more generalizable, the authors focused on this outcome when describing prediction zones. Patients with 40% or higher PEFR after third treatment had an 89% probability of reaching 50% predicted in 12 hours, while those with a third-treatment PEFR lower than 32% predicted had only a 22% probability.

CONCLUSIONS

A simple objective measure of pulmonary function early in treatment discriminated among those with high, low, and intermediate probabilities of achieving a specified level of PEFR within 12 hours. Awareness of this probability could assist clinicians attempting to predict discharge from the EDTU and facilitate decision making regarding utilization of EDTU resources.

Closed fractures of the tibial shaft. A meta-analysis of three methods of treatment

We reviewed the literature to determine the clinical outcomes of the treatment of closed fractures of the tibial shaft with immobilization in a cast, open reduction with internal fixation, or fixation with an intramedullary rod. We reviewed 2372 reports of comparative trials and uncontrolled studies of series of patients published between 1966 and 1993. Nineteen reports, involving six controlled trials and twenty-seven groups of patients, met our inclusion criteria. A structured questionnaire was used to assess the quality of the literature in terms of the experimental design and the method of assessment of outcome. Outcomes from controlled trials were summarized with odds ratios and risk differences, and outcomes from case series were summarized by the medians of the reported results. The studies that were reviewed generally had few subjects and were poorly designed. The comparative trials showed treatment with a cast to be associated with a lower rate of superficial infection than open reduction and internal fixation (mean difference, -5.81 per cent; p = 0.02) and open reduction and internal fixation to be associated with a higher rate of union by twenty weeks than treatment with a cast (mean difference, -18.07 per cent; p = 0.008). There were no other significant associations. There were insufficient data for us to evaluate any aspect of functional status, level of pain, or other patient-reported outcomes of any of the methods of treatment. The results of the present review suggest that the data from the published literature are inadequate for decision-making with regard to the treatment of closed fractures of the tibia.

The family experiences of narcotic addicts and their subsequent parenting practices

This survey study of male and female narcotic addicts participating in methadone maintenance programs examined self-reported retrospective data on parental behavior experienced by addicts during their adolescent years. These findings were contrasted with the addicts' self-report of their current parenting practices with their own adolescent children. Results showed addicts as perceiving their mothers as significantly more functional in their parenting practices than their fathers on indices of parental involvement, attachment, and responsibility. Significant parenting differences between addicts and their parents were reported for the three indices mentioned, as well as for parent discipline and punitive actions, with the addicts rating their current parenting practices as more effective than those of their parents. Reported parenting practices were further analyzed in the context of how the ratings of parental functioning were related to problems of drug and alcohol abuse exhibited in the home. Findings are discussed in terms of the implications for prevention and treatment approaches for addicts and their children.

Prediction of relapse within eight weeks after an acute asthma exacerbation in adults

Associations between historical, presenting, and treatment-related characteristics and relapse within 8 weeks after a moderate to severe asthma exacerbation were studied in a cohort of 284 adult asthmatics. Data were collected prospectively, and a multivariate model was developed and internally validated. Within 10 days, only 8% had relapsed, increasing to 45% by 8 weeks. Three variables that could be identified at the time of discharge were independently associated with relapse. These included: having made three or more visits to an emergency department in the prior 6 months (hazard ratio (HR) = 2.3, 95% CI = 1.6-3.4); difficulty performing work or activities as a result of physical health in the 4 weeks prior (HR = 2.7, 95% CI = 1.6-4.3); discontinuing hospital-based treatment for the exacerbation within 24 hours without having achieved a peak expiratory flow rate of at least 50% of predicted (HR = 2.6, 95% CI = 1.6-4.1). These risk factors may help to identify patients with poorly controlled asthma in need of more intensive and comprehensive management.

A comparison between emergency diagnostic and treatment unit and inpatient care in the management of acute asthma

BACKGROUND

Emergency diagnostic and treatment units (EDTUs) may provide an alternative to hospitalization for patients with reversible diseases, such as asthma, who fail to adequately respond to emergency department therapy.

OBJECTIVE

To evaluate the medical and cost-effectiveness, patient satisfaction, and quality of life of patients receiving EDTU care for acute asthma compared with inpatient care.

METHODS

A prospective, randomized clinical trial performed at 2 urban public hospitals enrolled patients with acute asthma (age range, 18-55 years) not meeting discharge criteria after 3 hours of emergency department therapy. Patients were treated with inhaled adrenergic agonists and steroids in an EDTU for up to 9 hours after randomization or with routine therapy in a hospital ward. Patients were followed up for 8 weeks.

MAIN OUTCOME MEASURES

Discharge rate from the EDTU, length of stay, relapse rates, days missed from work or school, days incapacitated during waking hours, symptom-free days and nights, nocturnal awakenings, direct medical costs, patients satisfaction, and patient quality of life.

RESULTS

The study consisted of 222 patients with asthma. Sixty-five patients (59%) treated in an EDTU were discharged home; the remainder were admitted to the hospital. There were no differences during the follow-up period in relapse rates (P = .74) or in any other morbidities between the EDTU and inpatient groups. There were significant differences in the length of stay, patient satisfaction, and quality of life favoring EDTU care. The mean (+/-SD) cost per patient in the EDTU group was $1202.79 +/- $1343.96, compared with $2247.32 +/- $1110.18 for the control group (P < .001).

CONCLUSIONS

Treatment of selected patients with asthma in an EDTU results in the safe discharge of most such patients. This study suggests that quality gains and cost-effective measures can be achieved by the use of such units.

An evaluation of a chest pain diagnostic protocol to exclude acute cardiac ischemia in the emergency department

BACKGROUND

Although accelerated diagnostic protocols are being increasingly used in emergency departments to diagnose acute cardiac ischemia, there have been no prospective evaluations of a chest pain diagnostic protocol with serial determinations of creatine kinase MB isoenzyme and mandatory exercise electrocardiography (ExECG).

METHODS

Prospective cross-sectional study in which chest pain protocol results were compared with final (reference) diagnoses of acute cardiac ischemia (including acute myocardial infarction and unstable angina). Patients in need of hospital admission but at low probability (by a validated algorithm) for acute myocardial infarction were examined for exclusions: known coronary artery disease, cardiac complications, severe comorbidities, or inability to perform exercise testing. A 12-hour diagnostic protocol included serial measurements of creatine kinase MB, ECG, and clinical assessments followed by ExECG for those with negative initial serial testing. Reference diagnoses were established during hospitalization and diagnostic accuracy was assessed.

RESULTS

The study group of 317 patients was 54% male and 65% black, and had a mean age of 46.6 years; 9.5% had a final diagnosis of acute cardiac ischemia. For this diagnosis, the protocol had a sensitivity of 90.0% (95% confidence interval, 72.3%-97.4%); specificity, 50.5% (95% confidence interval, 44.6%-56.4%); positive predictive value, 16.0%; and negative predictive value, 98.0%. Creatine kinase MB, serial ECGs, and ExECG each made a contribution to improved sensitivity and accuracy, whereas clinical reassessments were less discriminating, as indicated by protocol's receiver operating characteristic curve.

CONCLUSIONS

A chest pain diagnostic protocol achieved high sensitivity and improved specificity over the standard emergency department workup. There were no adverse advents associated with early ExECG.

Feasibility of a rapid diagnostic protocol for an emergency department chest pain unit

STUDY OBJECTIVE

To evaluate the applicability of a short-stay protocol for exclusion of acute ischemic heart disease without hospital admission and to analyze these results in the context of a conceptual model.

METHODS

An observational study of patients who presented with chest pain to the emergency department of an 886-bed inner-city municipal hospital and who needed hospital admission to rule out acute myocardial infarction (AMI). Patients were assessed by ED attending physicians to determine eligibility for an alternative, 12-hour protocol in an ED chest pain observation unit (CPOU) followed by immediate exercise testing. Outcome measures were proportion of patients eligible for the short-stay protocol, risk factor profile, and reasons for exclusion.

RESULTS

Of 500 patients screened, 446 had sufficient data points to determine protocol eligibility. Of these, 238 (53.3%; 95% confidence interval [CI], 48.7% to 57.9%) were found to have low probability for AMI. After study exclusion criteria were applied to the patient cohort, 63 patients (14.1%; 95% CI, 10.9% to 17.3%) were eligible for the protocol. The most common reasons for exclusion were history of coronary artery disease (46%) and inability to perform an interpretable exercise tolerance test (42%).

CONCLUSION

Although most admitted patients with chest pain (53%) were at low probability for AMI, only a minority (14%) were eligible for a short-stay protocol that required patients to be free of known coronary artery disease and able to perform an exercise tolerance test. Factors affecting the operations and efficiency of a CPOU include clinical characteristics of the target patient population, protocol tests used, and hospital occupancy and reimbursement patterns.

Patient satisfaction with an emergency department chest pain observation unit

STUDY OBJECTIVE

Patient satisfaction is an essential outcome measure in the diagnosis and treatment of acute chest pain in the emergency department. We compared patient satisfaction with the diagnostic protocol of a chest pain observation unit (CPOU) and standard inpatient hospitalization.

METHODS

We prospectively studied patients who presented to the ED with chest pain and were found to have a low risk of acute myocardial infarction (AMI) but who still might have benefited from a diagnostic protocol to rule out AMI. Consenting patients (N = 104) were randomized to the CPOU (experimental) arm or the hospital inpatient (control) arm and assessed for satisfaction by means of an interview before hospital discharge.

RESULTS

The CPOU protocol scored higher on four summary ratings of overall patient satisfaction. Correlations between overall satisfaction, number, and type of problems with care, and patient characteristics demonstrated content validity and revealed strengths and improvements that might be made in CPOUs.

CONCLUSION

Patients were more satisfied with rapid diagnosis in the CPOU than with inpatient stays for acute chest pain. Our findings add important information to the standard practice of weighing clinical and cost outcomes between two medical care alternatives.

A twin study of the association of post-traumatic stress disorder and combat exposure with long-term socioeconomic status in Vietnam veterans

This study examines the association between post-traumatic stress disorder (PTSD) and combat exposure with the socioeconomic status of 2210 male monozygotic veteran twin pairs in 1987. In the unadjusted analysis on individuals, modest correlations indicated that those with PTSD were more likely to have been divorced, and less likely to be currently employed or to achieve high status in income, education or occupation. In the crude analysis of veterans not suffering from PTSD, there were small positive correlations between combat level experienced and the likelihood of ever being married, ever being divorced, and the number of years employed at the current job. However, when we examined identical twins discordant for PTSD, and adjusted for pre-military and military service factors, only unemployment remained significant. Likewise, in combat-discordant twins, no significant effects on the socioeconomic indicators were seen. We conclude that PTSD and combat experience in Southeast Asia have not had a major impact on the socioeconomic status of veterans.

Insomnia in Vietnam era veteran twins: influence of genes and combat experience

Genetic and environmental influences on insomnia were studied in 2,825 pairs of Vietnam era veteran male twins. The self-reported sleep problems studied included trouble falling asleep, trouble staying asleep, waking often, waking tired and a composite sleep scale. Twin correlations for each of the sleep problems were larger in monozygotic than in dizygotic pairs, with heritability estimates ranging from 0.21 to 0.42. There was no effect of common familial environment. Phenotypic correlations for combat experience and sleep problems were small, ranging from 0.00 to 0.09, with no differences seen in monozygotic and dizygotic twins. When the effects of genes and combat exposure were evaluated simultaneously, there was a significant genetic contribution to all sleep measures, but combat exposure was significantly associated only with overall sleep quality, waking often and having trouble staying asleep.

A metabolically stable analog of 1,4,5-inositol trisphosphate activates a novel K+ conductance in pyramidal cells of the rat hippocampal slice

IP(s)3, a metabolically stable analog of 1,4,5-inositol trisphosphate (IP3), inhibited action potential firing when injected into hippocampal pyramidal cells. This effect was associated with decreased input resistance, a more negative resting potential, outward rectification at depolarized potentials, and an afterhyperpolarization. The response to IP(s)3 was unaffected by antagonists of Na+, Ca2+, and Cl- conductances, but was sensitive to changes in extracellular K+ concentration. The IP(s)3-induced conductance was voltage-dependent, was activated in 10 ms with depolarization, and was blocked by extracellular Ba2+ or intracellular Ca2+ chelation. It was not suppressed by other K+ conductance antagonists. Thus, IP(s)3 may activate a novel K+ conductance in CA1 pyramidal cells. IP3 itself did not elicit this conductance, suggesting it may be rapidly metabolized in these cells.

Calcium-dependent pirenzepine-sensitive muscarinic response in the rat hippocampal slice

Using intracellular recording techniques in the rat hippocampal slice, we observed that muscarinic agonists produce a transient Ca2+-dependent depolarization that may be related to the phosphatidylinositol cycle. First, it was more readily produced by muscarinic group A agonists, which strongly enhance the breakdown of phosphatidylinositol-4,5-bisphosphate (PIP2) than by group B agonists, which are less efficacious. Second, the Ca2+-dependent response was blocked by pirenzepine (PRZ), a selective muscarinic antagonist that blocks PIP2 breakdown in forebrain. Both group A and group B muscarinic agonists caused equivalent maintained levels of depolarization that were relatively insensitive to PRZ. The data suggest that the Ca2+-dependent response is fundamentally unlike other muscarinic responses that have been described in hippocampus.

Papain effects on rat hippocampal neurons in the slice preparation

Intracellular recordings were made from the CA1 stratum pyramidale region of rat hippocampal slices. Papain was applied to the cells via bath perfusion, and its effects on membrane properties, synaptic potentials and responses to pressure application of gamma-aminobutyric acid (GABA) were assessed. Papain did not markedly affect neuronal input resistance, resting potential or action potentials with treatment times lasting over one hour. Synaptic potentials were initially enhanced and then gradually abolished, with the fast inhibitory postsynaptic potential being the most sensitive and the late, potassium-dependent hyperpolarization being the most resistant to enzyme. Responses to GABA were enhanced by papain, the GABA-activated conductance increased, and a slow depolarizing wave appeared which resembled the effect caused by pentobarbital on these neurons. This study indicates that the use of papain in the acutely dissociated neuron preparation is not responsible for the dramatic increase in resting input resistance seen in these neurons. The GABA-activated conductance may be affected by the enzyme.

Cholinergic phosphatidylinositol modulation of inhibitory, G protein-linked neurotransmitter actions: electrophysiological studies in rat hippocampus

In electrophysiological studies using the rat hippocampal slice preparation, cholinergic agonists and phorbol 12,13-diacetate, a stimulator of protein kinase C, block the inhibitory actions of baclofen, a gamma-aminobutyric acid B receptor agonist, and adenosine. Relative potencies of cholinergic agonists in stimulating the phosphatidylinositol system, as measured biochemically, parallel their activity in blocking adenosine assessed electrophysiologically. Electrical stimulation of cholinergic afferents also reverses adenosine's inhibitory action. These findings indicate that stimulation of protein kinase C by the phosphatidylinositol system mediates cholinergic blockade of adenosine and baclofen. As these inhibitory agonists act by way of receptors linked to GTP-binding proteins, protein kinase C's inactivation of the GTP-binding protein involved may account for this cholinergic action.

Sodium-potassium pump inhibitors increase neuronal excitability in the rat hippocampal slice: role of a Ca2+-dependent conductance

We have used the rat hippocampal slice preparation as a model system for studying the epileptogenic consequences of a reduction in neuronal Na+-K+ pump activity. The cardiac glycosides (CGs) strophanthidin and dihydroouabain were used to inhibit the pump. These drugs had readily reversible effects, provided they were not applied for longer than 15-20 min. Hippocampal CA1 pyramidal cells were studied with intracellular recordings; population spike responses and changes in extracellular potassium concentration ([K+]o) were also measured in some experiments. This investigation focused on the possibility that intrinsic neuronal properties are affected by Na+-K+ pump inhibitors. The CGs altered the CA1 population response evoked by an orthodromic stimulus from a single spike to an epileptiform burst. Measurements of [K+]o showed that doses of CGs sufficient to cause bursting were associated with only minor (less than 1 mM) changes in resting [K+]o. However, the rate of K+ clearance from the extracellular space was moderately slowed, confirming that a decrease in pump activity had occurred. Intracellular recording indicated that CG application resulted in a small depolarization and apparent increase in resting input resistance of CA1 neurons. Although CGs caused a decrease in fast gamma-aminobutyric acid mediated inhibitory postsynaptic potentials (IPSPs), CGs could also enhance the latter part of the epileptiform burst induced by picrotoxin, an antagonist of these IPSPs. Since intrinsic Ca2+ conductances comprise a significant part of the burst, this suggested the possibility that Na+-K+ pump inhibitors affected an intrinsic neuronal conductance. CGs decreased the threshold for activation of Ca2+ spikes (recorded in TTX and TEA) without enhancing the spikes themselves, indicating that a voltage-dependent subthreshold conductance might be involved. The action of CGs on Ca2+ spike threshold could not be mimicked by increasing [K+]o up to 10 mM. A variety of K+ conductance antagonists, including TEA, 4-AP, Ba2+ (in zero Ca2+), and carbachol were ineffective in preventing the CG-induced threshold shift of the Ca2+ spike. The shift was also seen in the presence of a choline-substituted low Na+ saline. Enhancement of a slow inward Ca2+ current is a possible mechanism for the decrease in Ca2+ spike threshold; however, it is impossible to use the Ca2+ spike as an assay when testing the effects of blocking Ca2+ conductances. Therefore, we studied the influence of CGs on the membrane current-voltage (I-V) curve, since persistent voltage-dependent conductances appear as nonlinearities in the I-V plot obtained under current clamp.(ABSTRACT TRUNCATED AT 400 WORDS)

Use-dependent depression of IPSPs in rat hippocampal pyramidal cells in vitro

We have used intracellular recording techniques to study the use-dependence of evoked inhibitory postsynaptic potentials (IPSPs) in rat CA1 hippocampal pyramidal cells. We determined reversal potentials and conductance changes associated with IPSPs and responses to directly applied gamma-aminobutyric acid (GABA). The IPSP depression could be seen after a single conditioning stimulus. This depression appeared to be due primarily to a 50% decrease in IPSP conductance (gIPSP). Trains of stimulating pulses (50 pulses at 5 or 10 Hz) produced more pronounced effects than a single conditioning pulse. Suprathreshold repetitive stimulation of stratum radiatum (SR) produced epileptiform burst firing and greater depression of IPSPs than did alvear (ALV) or subthreshold SR stimulation. During suprathreshold SR stimulation the IPSP was nearly abolished and the membrane potential could become less negative than the resting potential. A masking effect of facilitated depolarizing potentials on IPSPs was unlikely since IPSPs accompanied by little or no depolarizing potential were also depressed by SR trains. The 75% reduction in IPSP conductance found after repetitive stimulation confirmed that an overlapping conductance was not responsible for the depression of the IPSP. The GABA-induced conductance increase was not depressed by identical trains. Trains of stimulation induced depolarizing shifts in equilibrium potentials for the IPSP (EIPSP) and GABA (EGABA) of approximately 10 mV. These shifts were always greater after SR trains than after ALV trains. Simultaneous recordings of membrane potential and extracellular potassium concentration ([K+]o) with K+-sensitive microelectrodes revealed a direct correlation between the two during a stimulus train. Membrane potential depolarized as much as 18 mV from the peak of the IPSP and [K+]o could increase to a maximum of 10 mM during some trains. A depressant effect (of approximately 50%) of K+ on IPSPs was demonstrated by brief pressure ejection of K+ near the soma. We conclude that repetitive stimulation depresses gIPSP and shifts EIPSP in the depolarizing direction. Whereas gIPSP began to decline after a single conditioning pulse, the additional depression of IPSPs produced by stimulus trains was due in large part to shifts in EIPSP. Depression of gIPSP was not due to desensitization or block of ionic conductances, since gGABA was not reduced. The EIPSP may change as a result of increases in [K+]o.

Spectral analysis of kindled hippocampal afterdischarges in lead-treated rats

Male rats were exposed to lead from parturition through weaning. When subjected to electrical hippocampal kindling as adults, although there were no alterations in the kindling rates, lead-treated animals were found to differ from controls in several other respects. In contrast to controls, lead-treated animals did not show an increase in afterdischarge (AD) duration with kindling, and the power spectrum of the AD did not shift to a higher peak frequency. There was a clear dose-related effect of lead on the spectra of the kindled AD, which in lead-treated groups was characterized by greater power in the low-frequency bands. These data indicate that long-lasting dysfunction can occur following a brief neonatal lead exposure. Power spectral techniques may be useful for future studies in neurotoxicology and epilepsy.

Neonatal lead exposure in rats: II. Effects on the hippocampal afterdischarge

Male Sprague-Dawley rats were exposed to lead from parturition to weaning via the dams' milk. Dams were provided with drinking water containing 1.0 (LL), 2.5 (ML), or 5.0 (HL) mg/ml lead acetate or 1.25 (C) mg/ml sodium acetate. Beginning at 15 weeks of age, characteristics of the electrically elicited hippocampal afterdischarge (AD) and its alteration by phenytoin (PHT) were assessed in these rats. A separate group of rats was sacrificed at 20 weeks for hippocampal metal analysis. Increases in primary AD duration were observed in LL and ML, significant in ML. Significantly fewer wet dog shakes occurred in all lead groups. HL animals displayed shorter rebound ADs. All groups responded to PHT with increases in primary AD duration, but the increases in the ML and HL groups were significantly greater than in the C group. Hippocampal lead, zinc, and copper were not different from control. It is concluded that a brief lead exposure can have persistent effects on hippocampal function and that these effects are not due to altered hippocampal metal concentrations. The findings are discussed in relation to the known effects of postnatal lead exposure on hippocampal neuronal development.

Neonatal lead exposure in rats: I. Effects on activity and brain metals

Upon parturition, Sprague-Dawley dams were administered 1.0 (LL), 2.5 (ML), 5.0 (HL) mg/ml of lead acetate or 1.25 mg/ml sodium acetate (C) in their drinking water. Pups were weaned to tap water at 22 days of age. The developmental pattern of neonatal activity was characterized by monitoring spontaneous activity of single pups for 30 minutes on days 12, 14, 16, 18, 20, and 22, and for one hour in adults. Brains were removed at weaning for subsequent analyses of lead, zinc, and copper. The effects of lead on neonatal activity were considered to be minor because only the ML group differed significantly from C and exhibited hyperactivity on day 16. Adult activity levels, however, were decreased in a dose-dependent fashion. At 22 days of age, whole brain metal analyses revealed a dose-dependent increase in lead levels and a decrease in zinc. These results do not strongly support a hypothesis of lead-induced neonatal hyperactivity.

On the possibility of simultaneously recording from two cells with a single microelectrode in the hippocampal slice

Unusual cellular elements have been recorded intracellularly in the CA1 region of the rat hippocampal slice. The elements appear, by all electrophysiological criteria except one, to be glia. However, unlike glia, they can fire action potentials. We suggests that these recordings represent cases of artifactual coupling of two cells by a recording microelectrode. The results have implications for the interpretation of dye injection experiments in the hippocampal CA1 region.