Rita Acampora

Vascular Effects of Acute Hyperglycemia in Humans Are Reversed by l-Arginine Evidence for Reduced Availability of Nitric Oxide During Hyperglycemia

BACKGROUND Acute hyperglycemia may increase vascular tone in normal humans via a glutathione-sensitive, presumably free radical-mediated pathway. The objective of this study was to investigate whether or not the vascular effects of hyperglycemia are related to reduced availability of nitric oxide. METHODS AND RESULTS Acute hyperglycemia (15 mmol/L, 270 mg/dL) was induced in 12 healthy subjects with an artificial pancreas. Systolic and diastolic blood pressures, heart rate, and plasma catecholamines showed significant increases (P < .05) starting after 30 minutes of hyperglycemia; leg blood flow decreased significantly (15%; P < .05) at 60 and 90 minutes. Platelet aggregation to ADP and blood viscosity also showed significant increments (P < .05). The infusion of L-arginine (n = 7, 1 g/min) but not D-arginine (n = 5, 1 g/min) or L-lysine (n = 5, 1 g/min) in the last 30 minutes of the hyperglycemic clamp completely reversed all hemodynamic and rheological changes brought about by hyperglycemia. Infusion of NG-monomethyl-L-arginine (L-NMMA; 2 mg/min) to inhibit endogenous nitric oxide synthesis in 8 normal subjects produced vascular effects qualitatively similar to those of hyperglycemia but quantitatively higher (P < .05); however, heart rate and plasma catecholamine levels decreased during L-NMMA infusion, presumably as a consequence of baroreflex activation. Infusion of L-NMMA during hyperglycemia produced changes not different from those obtained during infusion of L-NMMA alone. CONCLUSIONS The results show that acute hyperglycemia in normal subjects causes significant hemodynamic and rheological changes that are reversed by L-arginine. Moreover, the effects of hyperglycemia are mimicked to a large extent, but not entirely, by infusion of L-NMMA. This suggests that hyperglycemia may reduce nitric oxide availability in humans.

Metabolic and Cardiovascular Effects of Carvedilol and Atenolol in Non-Insulin-Dependent Diabetes Mellitus and Hypertension: A Randomized, Controlled Trial

Compared with the general population, diabetic patients have an approximately twofold increased risk for hypertension and are more susceptible to the vascular consequences of high blood pressure. Indeed, an estimated 35% to 75% of cardiovascular and renal complications in diabetic patients can be attributed to hypertension [1]. Treatment with -adrenergic antagonists has been shown to be associated with an increased risk for impaired glucose tolerance or diabetes; this has been attributed to the worsening of insulin resistance and the deterioration of lipoprotein metabolism caused by the agents [2]. All this has made physicians reluctant to prescribe -blockers for diabetic patients with hypertension, although cardioselective -blockers have reduced mortality associated with cardiovascular causes in secondary prevention trials [3]. Carvedilol is a multiple-action antihypertensive drug with nonselective -adrenoreceptor and selective -adrenoreceptor blocking activity [4]. Its ratio of 1-blocking potency to 1-blocking potency is 7.6:1 for a 50-mg dose [5]. In addition, carvedilol prevents lipid peroxidation and the depletion of endogenous antioxidants [6]. This may be particularly useful in diabetic patients who may have increased free-radical activity (oxidative stress) [7]. We compared the metabolic and cardiovascular effects of carvedilol with those of atenolol in diabetic patients with hypertension in a randomized, double-blind, controlled trial. Methods Participants Our research protocol was approved by our institutional review board, and informed consent was obtained from patients before participation. Men and women who had noninsulin-dependent diabetes mellitus and had a supine diastolic blood pressure of 90 to 105 mm Hg on at least two occasions at the end of a 4- to 6-week placebo run-in period were eligible to participate. All patients were referred from the outpatient department of our institution and were consecutively chosen. A total of 45 patients met the inclusion criteria and were randomly assigned to treatment. All but 3 patients completed the study. Study Design Our study had a randomized, double-blind design for parallel study groups. Patients who had blood pressure greater than 160/90 mm Hg or who were taking antihypertensive drugs entered a 4- to 6-week run-in period, during which placebo was given to replace the previous antihypertensive drug, if any. Routine hematologic and blood chemistry analyses (hematologic indices, serum sodium and potassium concentrations, liver enzyme levels, urea concentrations, and creatinine concentrations) were done during the initial screening and after the treatment period. Patients were randomly assigned to receive either carvedilol (25 mg once daily) or atenolol (50 mg once daily) in the morning for 24 weeks. After 4 weeks, patients whose diastolic blood pressure while seated was more than 90 mm Hg and had not decreased by at least 10 mm Hg had their dose of study medication doubled for the remaining 20 weeks of the study. A person who was not involved in trial management randomly assigned the patients using random numbers derived from published tables. The list of randomization numbers was used to label the drug boxes, which were given to the participants sequentially. Both patients and caregivers were blinded to treatment, and randomization codes were not broken until all laboratory measurements had been done. Cardiovascular and metabolic variables were checked at the end of the placebo period and at the end of the active treatment period. All participants were instructed to follow a weight-maintaining diet (50% carbohydrates, 30% lipids, 20% protein) for 3 days before the experiments were done. Side effects, concomitant diseases, and blood pressure were assessed by interview and physical examination every fourth week during treatment. Clinical and Laboratory Measurements Patients were asked to refrain from smoking and to fast overnight before each metabolic assessment was done. The euglycemic clamp technique was used to estimate insulin sensitivity in vivo by infusing insulin (1 mU/kg of body weight per minute) and glucose to keep plasma glucose levels at the baseline concentration [8]. At the unchanged plasma glucose concentrations, the amount of glucose required to maintain euglycemia equals whole-body glucose disposal and is expressed in mol/kg per minute (M). The insulin sensitivity index (M/insulin level during the clamp procedure) measures how effectively plasma insulin induces glucose uptake in insulin-sensitive tissues, such as muscle and fat. Substrate oxidation was estimated by indirect calorimetry [9]. On the day after calorimetry, the patients had an oral glucose tolerance test (75 g of glucose). On the third day, they had an insulin tolerance test (0.15 U/kg). Blood pressure was measured with appropriate cuff size three times after patients rested for 5 minutes in the supine position. Plasma glucose, insulin, glucagon, and epinephrine levels were measured as described elsewhere [10]; hemoglobin A1c (HbA1c) was measured by column chromatography (Bio-Rad, Milan, Italy); and cholesterol, triglyceride, and high-density lipoprotein cholesterol levels were determined enzymatically [9]. Left ventricular mass normalized by surface area was measured by echocardiography [9]. Serum levels of lipid peroxides were measured as reaction products of malondialdehyde with thiobarbituric acid (thiobarbituric-acid-reactive substances) according to the method of Waravdekar and Sadlaw [11], with slight modifications. Normal lipid peroxide values for our laboratory are 0.34 to 0.86 mol/L. Statistical Analysis All values in the tables are presented as the mean SD unless otherwise noted; 95% CIs are provided where appropriate. The areas under the glucose and insulin curves were calculated by trapezoidal rule [12]. Change was calculated as the value obtained at the end of intervention minus the value obtained at the beginning of intervention. A preliminary analysis of variance was used to assess the significance within and between groups. One-sample t-tests were used to compare values obtained before and after carvedilol or atenolol therapy, and two-sample t-tests were used for between-group comparisons. Results Three patients (two in the atenolol group and one in the carvedilol group) were unavailable for follow-up; they refused to complete the study and did not specify a reason. These patients dropped out early (between weeks 4 and 8) after randomization; analysis of the study results did not differ when the analysis was done according to actual treatment or according to intention to treat (we used the latter method). Compliance, determined by tablet count, was 94.5% in the carvedilol group and 95% in the atenolol group. The baseline characteristics of the 45 patients who completed the study are shown in Table 1. The two groups were similar at baseline. Body mass index did not change in either group after treatment. Approximately one third of patients in each group (32% in the carvedilol group and 35% in the atenolol group) required upward dose titration at week 4 because of inadequate response. At the end of treatment, 91% of patients receiving carvedilol and 85% of those receiving atenolol had a diastolic blood pressure while seated of less than 90 mm Hg or had their diastolic blood pressure decreased by more than 10 mm Hg (P > 0.2 for comparison). Average systolic and diastolic blood pressure and left ventricular mass decreased in both groups, but the differences between the groups were small (P > 0.2) (Table 2). The decrease in heart rate was greater in patients receiving atenolol than in those receiving carvedilol (P < 0.005). The decrease in mean triglyceride level was 0.56 mmol/L greater (P < 0.001) and the increase in high-density lipoprotein cholesterol level was 0.13 mmol/L greater (P < 0.001) with carvedilol than with atenolol. Table 1. Baseline Characteristics of the Study Patients Table 2. Effects of 24-Week Intervention with Carvedilol or Atenolol in 45 Patients with Non-Insulin-Dependent Diabetes Mellitus and Hypertension* Mean fasting plasma glucose and insulin levels decreased during carvedilol treatment and increased during atenolol treatment (Table 2). The HbA1c level decreased by 1.4% in the carvedilol group and increased by 4% in the atenolol group (P < 0.001 for the difference). Mean total glucose disposal and insulin sensitivity index increased during carvedilol treatment and decreased during atenolol treatment (P 0.01 for the difference). Serum levels of thiobarbituric-acid-reactive substances decreased by 0.25 mol/L in the carvedilol group and did not change in the atenolol group (P < 0.001 for the difference). The decreases in plasma glucose and insulin responses to the oral glucose load were 61 mmol/L 180 minutes greater (CI, 101 to 21 mmol/L 180 minutes; P = 0.035) and 6.2 nmol/L 180 minutes greater (CI, 9.8 to 2.6 nmol/L 180 minutes; P = 0.03), respectively, with carvedilol than with atenolol (data not shown). The plasma glucose level nadir occurred 60 minutes after the insulin bolus was administered and was not affected by either drug (P = 0.09) (data not shown). Glucagon and epinephrine responses to hypoglycemia were similar before and after treatment with both drugs (P > 0.08) (data not shown). Discussion Our results show that both carvedilol and atenolol effectively decrease blood pressure and ventricular mass in patients with diabetes and hypertension. They also show that the drug doses administered in this study are equivalent with regard to their ability to decrease blood pressure in these patients, who are particularly at risk for cardiovascular disease. The similarities between the two drugs end with their cardiovascular effects, however; their metabolic effects are different and, to a large extent, divergent. Fasting plasma glucose and insulin levels decreased during carvedilol treatment and increased during atenolol treatment. Th

Metformin Improves Glucose, Lipid Metabolism, and Reduces Blood Pressure in Hypertensive, Obese Women

OBJECTIVE To determine the effects of metformin on blood pressure, left ventricular mass, and some metabolic and endocrine parameters in nondiabetic, obese, hypertensive women. RESEARCH DESIGN AND METHODS Twelve obese, nondiabetic, hypertensive women received 850 mg metformin 2 times/day for 12 wk and placebo for another 12 wk, according to a double-blind, cross-over, randomized design. All patients were hospitalized 4 times, i.e., before randomization and after each treatment (metformin or placebo), to conduct metabolic and cardiovascular investigations (oral glucose tolerance test, euglycemic clamp associated with indirect calorimetry, and echocardiography). RESULTS Fasting glucose, HbA1c, fasting and glucose-stimulated insulin, blood pressure and left ventricular mass, cholesterol, triglycerides, and fibrinogen decreased significantly after metformin treatment, whereas high-density lipoprotein cholesterol increased. The improvement in glucose metabolism resulted from increased sensitivity to insulin. CONCLUSIONS These findings suggest that metformin treatment in obese, nondiabetic, hypertensive women produces a more favorable cardiovascular risk profile.

Metformin Improves Hemodynamic and Rheological Responses to L-Arginine in NIDDM Patients

OBJECTIVE The endothelium plays a pivotal role in the regulation of vascular tone by releasing nitric oxide (NO). Increased availability of L-arginine, the natural precursor of NO, induces vasodilatation and inhibits platelet activity. We studied the effect of metformin on hemodynamic and rheological responses to L-arginine in patients with NIDDM. RESEARCH DESIGN AND METHODS Ten newly diagnosed NIDDM patients with mild fasting hyperglycemia (7.5 ± 0.3 mmol/l) and without evidence of both micro- and macrovascular complications were investigated. They received an intravenous infusion of L-arginine (1 g/min for 30 min) with evaluation of plasma glucose and insulin, systolic (sBP) and diastolic (dBP) blood pressure, heart rate and plasma catecholamines, platelet aggregation, and blood viscosity and filterability. The L-arginine test was repeated after an 8-week treatment with metformin (850 mg b.i.d.). RESULTS Metformin treatment significantly reduced basal fasting plasma glucose, HbA1c, and platelet aggregation to ADP (P < 0.05); the other parameters did not change. During pretreatment test, L-arginine infusion decreased sBP (from 137 ± 4.1 to 129 ± 4.5 mmHg, P < 0.01) and dBP (from 79 ± 1.9 to 75 ± 1.2 mmHg, P < 0.01) without affecting heart rate or plasma catecholamines. Both platelet aggregation and blood viscosity showed significant decrements after L-arginine, while blood filterability did not change. After metformin treatment, the decrease in blood pressure after L-arginine infusion was significantly enhanced, with a maximal decrease of sBP of 12 ± 3.4 mmHg (8 ± 2.5 mmHg pretreatment, P < 0.05) and dBP of 9.5 ± 2.4 mmHg (4.5 ± 1.9 mmHg pretreatment, P < 0.01). Heart rate, plasma norepinephrine levels, and blood filterability also rose significantly (P < 0.05–0.01). The decrease in both platelet aggregation and blood viscosity after L-arginine was significantly amplified after metformin. CONCLUSIONS We conclude that L-arginine infusion in newly diagnosed NIDDM patients without vascular complications produces relevant hemodynamic and theological changes, which are amplified by an 8-week treatment with metformin. Whether these vascular effects of metformin will improve the poor cardiovascular outlook of the diabetic patient is still unknown.

Effects of Perindopril and Carvedilol on Endothelium-Dependent Vascular Functions in Patients With Diabetes and Hypertension

OBJECTIVE To compare the effects of the ACE inhibitor perindopril and the β-blocker carvedilol on blood pressure and endothelial functions in N1DDM patients with hypertension. RESEARCH DESIGN AND METHODS We conducted a double-blind randomized trial in 26 patients with NIDDM and mild hypertension. A 4-week run-in placebo period preceded the active 12-week treatment with perindopril (4–8 mg daily) or carvedilol (25–50 mg daily). Endothelial functions were assessed by evaluating the hemodynamic (mean blood pressure, leg blood flow) and rheological (platelet aggregation, blood viscosity, and blood filterability) responses to an intravenous bolus of 3 g L-arginine, the natural precursor of nitric oxide. RESULTS Both perindopril and carvedilol significantly reduced mean blood pressure (P < 0.001) and increased leg blood flow (P < 0.05) to the same extent; blood filterability remained unchanged in both perindopril- and carvedilol-treated groups. Carvedilol reduced platelet aggregation and blood viscosity significantly (P < 0.05) but perindopril did not. Before treatment, the hemodynamic and rheologic responses to L-arginine were significantly lower in patients (P < 0.05–0.01) than in 20 nondiabetic nonhypertensive control subjects. After 12 weeks of treatment, both drugs normalized the hemodynamic responses to L-arginine. Platelet aggregation response to L-arginine was ameliorated by carvedilol and remained unchanged in the perindopril group. CONCLUSIONS At the doses used, both drugs effectively reduce blood pressure and normalize the hemodynamic responses to L-arginine. The implications of the ameliorated endothelial function for the poor cardiovascular outlook of the NIDDM hypertensive patient need further assessment.

The Squatting Test: A Useful Tool to Assess Both Parasympathetic and Sympathetic Involvement of the Cardiovascular Autonomic Neuropathy in Diabetes

The heart rate responses observed after both squatting and standing are thought to be of reflex nature and may be useful to assess the functional integrity of parasympathetic and sympathetic nerves in diabetes. In the standard maneuver, each subject stood still for 3 min, then squatted down for 1 min, and at last stood up during an inspiratory phase. In 10 healthy subjects (25–31 years of age), lengthening of the R-R interval during squatting was abolished by atropine, whereas propranolol markedly attenuated shortening of the R-R interval at standing from squatting. Squatting test (SqT) ratios (SqT vagal [SqTv] = ratio between the R-R interval mean before squatting and the longest R-R interval after squatting; SqT sympathetic [SqTs] = ratio between the basal R-R interval and the shortest R-R interval at standing) were calculated in 558 healthy subjects and 346 diabetic patients (insulin-dependent diabetes mellitus/non-insulin-dependent diabetes mellitus: 103/243). Normal ranges (95 and 99% confidence intervals [CIs]) for subjects 20–74 years of age showed a statistically significant negative correlation with age. SqTv was outside the 99% CI in 145 (42%) diabetic patients and in 7 (1.3%) of the control subjects. The corresponding figures for SqTs were 40 and 0.8%, respectively. Age and duration of diabetes had a negative influence on SqT ratios. SqT ratios were compared with other reflex tests currently used for diagnosis of autonomic neuropathy: deep breathing (DB), lying-to-standing (LS), Valsalva manuever, and blood pressure change after standing (orthostatic hypotension [OH]). Autonomic involvement was arbitrarily defind as mild (one test pathologica), definite (two tests pathological), or severe (three or more tests pathological), definite (two tests pathological), or severe (three or more tests pathological). In patients with definite or severe involvement, Sqt ratios and DB anf LS tests showed the least overlap between healthy subjects and diabetic patients; however, for patients with mild or no autonomic involvement, SqT rations were significantly better than DB, LS, or OH tests. In conclusion, 1) SqT ratios can discriminate between healthy subjects and diabetic patients to an equal or greater extent than the other tests; 2) SqT ratios give information on both parasympathetic and sympathetic activity; and 3) SqT ratios are better than other single tests in identifying mild autonomic involvement. These results may be important for early intervention trials.

Tolrestat in the Primary Prevention of Diabetic Neuropathy

OBJECTIVE To compare the effects of tolrestat and placebo in patients with subclinical diabetic neuropathy. RESEARCH DESIGN AND METHODS Non-insulin-dependent diabetes mellitus (NIDDM) patients with early involvement of the autonomic nervous system were identified by only one pathological (outside the 99% confidence interval of the normal population) squatting test (vagal or sympathetic). Fifty-seven patients entered a randomized, placebo-controlled, double-blind, parallel 52-week study of tolrestat at a dose of 200 mg/day. Cardiovascular reflex tests (squatting vagal and sympathetic tests, pressure gain, deep breathing, lying-to-standing, Valsalva maneuver, and orthostatic hypertension), vibration thresholds, tendon reflexes, and muscle strength were assessed throughout the study. RESULTS At 12 months, nerve function significantly improved in patients receiving tolrestat and deteriorated in patients taking placebo. At baseline, the squatting vagal test was normal in 16 patients in the tolrestat group and in 15 patients in the placebo group. At 12 months, 25 patients taking tolrestat had a normalized squatting test, but only 6 patients taking placebo did (P = 0.02). Vibration perception threshold improved by a value of 6 ± 3 V in the tolrestat group (P < 0.001) and deteriorated by a value of 3 ± 1.8 V (P < 0.001) in the placebo group. CONCLUSIONS Tolrestat may be useful in the primary prevention of diabetic neuropathy.

Abnormal Rheologic Effects of Glyceryl Trinitrate in Patients with Non-Insulin-Dependent Diabetes Mellitus and Reversal by Antioxidants

Longitudinal data in patients with noninsulin-dependent diabetes mellitus indicate that major cardiovascular events, such as myocardial infarction and vascular death, may occur at a rate of 5% to 7% per year, even in persons who have had no known previous cardiovascular events [1]. Glycemic control, as assessed by hemoglobin A1c levels, predicts not only microvascular complications in diabetes [2] but also coronary heart disease mortality [3], peripheral arterial disease [4], and amputation of lower extremities [5]. Hyperglycemia may be related to vascular disease through abnormalities in lipoprotein particle composition, oxidation of low-density lipoproteins, alterations in the coagulation system, and irreversible glycosylation of proteins. It has been suggested that the increased oxidative stress of diabetes may be a link between hyperglycemia and vascular complications in diabetes [6]. Organic nitrate esters, such as glyceryl trinitrate and isosorbide dinitrate, are potent vasodilators that have been used extensively in cardiovascular therapy. About one third of patients with diabetes who have coronary artery disease may be receiving treatment with organic nitrates [7]. Increasing evidence suggests that the action of organic nitrates derives from metabolic conversion to nitric oxide, which relaxes the underlying vascular smooth muscle by increasing the production of cyclic guanosine monophosphate [8]. The availability of intracellular sulfhydryl groups, probably from glutathione and cystine, is thought to be important in the biotransformation of organic nitrates to nitric oxide [9]. The amount of intracellular thiol groups is likely to be depleted in patients with diabetes because of the increased oxidative stress brought about by hyperglycemia [10]. This may reduce the vascular effects of organic nitrates in patients with diabetes. Consistent with this possibility, impaired forearm vasodilatory response to glyceryl trinitrate, but not to the direct-acting nitric-oxide-donor sodium nitroprusside, has been seen in patients with diabetes compared with persons without diabetes [11]. Blood viscosity is now considered to be a major cardiovascular risk factor [12, 13] and has been implicated in vascular complications in diabetes [14, 15]. Surprisingly, knowledge of the influence of organic nitrates on blood rheology is lacking. We investigated the hemorrheologic and hemodynamic effects of short- and long-acting glyceryl trinitrate preparations in patients with diabetes compared with controls. We also evaluated the effects of glutathione and vitamin E to find out whether antioxidant supplementation could modify responses to glyceryl trinitrate in patients with diabetes. Methods Patients We studied 80 persons who were 44 to 65 years of age. Forty patients with diabetes were recruited from the outpatient departments of our institutions. All had noninsulin-dependent diabetes mellitus, had been older than 40 years of age at diagnosis, had had diabetes for fewer than 10 years, and had no clinical or laboratory evidence of coronary or peripheral artery disease. They were normotensive and were receiving no drugs other than therapy for diabetes (sulfonylureas or biguanides). Controls were 40 healthy laboratory staff members matched to the patients with diabetes for age, sex, and smoking status. They were receiving no drugs. The clinical characteristics of both groups are shown in Table 1. The study was approved by the local ethics committee, and all participants gave written informed consent. Table 1. Characteristics of Controls and Patients with Diabetes* Procedures All participants were studied while fasting in the morning and lying supine. Special care was taken to ensure that drugs containing aspirin or related compounds had not been used recently. Smoking was not permitted on the test day. For automatic recording of systolic, diastolic, and mean arterial pressure and heart rate, the participants were instrumented with a noninvasive device (Finapres, Ohmeda 2300, Englewood, California) that has been shown to be as accurate as intra-arterial blood pressure measurement techniques [16]. Ventricular function was assessed using echocardiography. The study started after the participants had rested for at least 30 minutes and after three consecutive measurements of blood pressure and heart rate had differed by less than 5%. Twenty patients with diabetes and 20 matched controls were each given a single sublingual dose of glyceryl trinitrate (0.3 mg), and hemodynamic values were recorded 15 and 60 minutes later. At these times, adequate blood samples without stasis were taken for rheologic measurements. The participants repeated the test twice more, after receiving vitamin E, 300 mg/d orally, for 7 days (Evitum, Lipha, Calenzano, Italy) and during glutathione infusion (Tationil, Boehringer Mannheim, Milan, Italy). Glutathione infusion (600 mg as an intravenous bolus followed by 600 mg/h) was started 30 minutes before and was continued for 60 minutes after administration of glyceryl trinitrate. The three tests were separated by at least 7 days and were done in random order. The effects of transdermal glyceryl trinitrate patches (Adesitrin, Pharmacia, Milan, Italy; 10 mg/d) were investigated in the other 20 patients with diabetes and 20 matched controls; hemorrheologic and hemodynamic measurements were taken after 1 hour and after 12 hours. The protocol was repeated after the participants had received vitamin E, 300 mg/d, and glutathione, 600 mg/d intramuscularly, for 7 days. One half of participants put the patch on at 8:00 a.m., and the other half put it on at 8:00 p.m., in random order. The sequence of the three tests was randomized. Blood Rheology Platelet aggregation response induced by 0.5 and 1.25 mol of adenosine diphosphate was determined according to the method of Born [17]. Aliquots of blood anticoagulated with 0.77 mol/L of ethylenediaminetetraacetic acid (the ratio of blood to ethylenediaminetetraacetic acid was 1:20) were used to assess blood viscosity at high shear rates (450 s1) using a Brookfield Digital Viscosimeter 0.8-degree cone (Brookfield Engineering Laboratories, Stoughton, Massachusetts). Blood filterability was determined according to the method of Reid and coworkers [18]. Hematocrits were determined by centrifuging blood samples in glass capillary tubes for 5 minutes at 12000 revolutions per minute. All determinations were made in duplicate by a person blinded to participants and treatments. Coefficients of variation were 2% for blood viscosity, 3% for blood filterability, and 5% for platelet aggregation. In Vitro Studies Studies were done in vitro on aliquots of blood taken from 10 patients with diabetes and 10 matched controls. Platelet aggregation response to adenosine diphosphate was done after incubation of platelet-rich plasma with glyceryl trinitrate (100 and 200 ng/mL, end concentration) for least 5 minutes at 37 C. Glyceryl trinitrate was freshly prepared in distilled water, shielded from light, and incubated for at least 5 minutes before blood viscosity and filterability were determined. Glutathione was tested at the end concentration of 200 g/mL. Statistical Analysis All data are presented as mean SE; 95% CIs are provided when appropriate. Pairs of means were assessed using the Student t-test. Hemorrheologic and hemodynamic responses to drugs in vivo were analyzed by repeated measures analysis of variance. The test primarily analyzed the differences between the matched pairs (for example, patients with diabetes compared with controls and patients with diabetes compared with themselves) as between-subjects effects and then tested time and group as within-subjects effects. In the in vitro studies, dose was considered to be a within-subjects factor. Each group of patients with diabetes was studied three times (with glyceryl trinitrate alone, with glyceryl trinitrate and vitamin E, and with glyceryl trinitrate and glutathione). To correct for the correlations between measurements (both within patients and over time), an adequate wash-out period between different tests was allowed to elapse, and a Square Latin model (program 4V of BMDP) was introduced into the linear model of the analysis. Post hoc testing was done using the Scheffe test. A further adjustment for baseline differences was made considering the differences between baseline and follow-up measures seen in the four groups (differences of differences). Relations were determined using linear regression analysis. BMDP software was used. Results The two groups were well matched (Table 1). At baseline, platelet aggregation and blood viscosity were significantly higher and blood filterability was significantly lower in patients with diabetes than in controls. In all participants, there was a significant inverse relation between blood viscosity and filterability (r = 0.51 [95% CI, 0.6 to 0.42]; n = 80; P < 0.001). In patients with diabetes, there was a significant positive relation between hemoglobin A1c levels and blood viscosity (r = 0.32 [95% CI, 0.24 to 0.41]; n = 40; P = 0.029). Heart rate increased from 76 1.5 beats/min to 82 1.5 beats/min (15-minute value; P < 0.01), whereas ejection fraction (from 0.51 0.023 to 0.42 0.022; P < 0.01) and mean blood pressure (from 96 1.7 to 93 1.7 mm Hg; P = 0.041) decreased significantly after sublingual administration of glyceryl trinitrate in controls. Baseline values were re-established within 60 minutes of administration. Platelet aggregation responses to adenosine diphosphate (both doses), blood viscosity, and blood filterability showed significant improvements after glyceryl trinitrate; these persisted until 60 minutes after administration (Figure 1). Figure 1. Blood filterability and viscosity and platelet aggregation at baseline and 15 and 60 minutes after administration of sublingual glyceryl trinitrate (0. P P Heart rate (from 77 1.8 beats/min to 78 1.7 beats/min), mean blood pressure (from

Hemodynamic and metabolic effects of transdermal clonidine in patients with hypertension and non-insulin-dependent diabetes mellitus.

The aim of this study was to evaluate the effect of transdermal clonidine on hemodynamic and metabolic parameters in patients who have elevated blood pressure and non-insulin-dependent diabetes mellitus (NIDDM). After a 2-week run in placebo period, 20 NIDDM patients who had diastolic blood pressure in the range of 90 to 105 mm Hg underwent a randomized, single blind, placebo controlled, cross-over study of 4 week treatment with clonidine (transdermal patch 2.5 mg/week) or placebo (inactive patch). Compared with placebo, clonidine significantly reduced systolic (153 +/- 6 v 163 +/- 8) and diastolic (88 +/- 2 v 98 +/- 3.5 mm Hg, P = .001) blood pressure, left ventricular mass (94 +/- 11 v 99 +/- 12 g/m2, P < .01) and fasting glucose levels. Total glucose disposal (glucose clamp) was 6.5 +/- 1.5 with placebo and 7.1 +/- 1.6 mg/kg/min with clonidine (P < .01). Oxidative glucose disposal (indirect calorimetry) was also greater after clonidine. Plasma glucose, insulin, and C-peptide responses following oral glucose (75 g) were significantly lower after clonidine, as well as urinary albumin excretion. Transdermal clonidine is effective in reducing blood pressure in hypertensive NIDDM patients and is well tolerated. It may be useful to reduce the cardiovascular impact of hypertension in diabetes mellitus.

Hyperinsulinemia in glucose intolerance: Is it true?

To evaluate whether beta-cell hyperfunction characterizes glucose intolerant states per se independent of fasting glycemia, we conducted a case-control study among 430 subjects who were classified, by NDGG criteria, as having normal glucose tolerance (n=230, 130M/130F), nondiagnostic tolerance (NDT, n=100, 50M/50F) and impaired glucose tolerance (IGT, n=100, 50M/50F). Thirty-four subjects (17M/17F) with normal glucose tolerance were matched by age, sex, body mass index (BMI), waist-to-hip ratio (WHR), fasting glucose and HbA1c with 30 NDT (15M/15F) and 30 IGT (15M/15F) subjects. The continuous and significant increase in insulin and C-peptide levels across categories of glucose tolerance (from normal to NDT to IGT) was no longer evident in the case-control study: at a fasting plasma glucose ranging from 5.2–5.5 mmol/L (HbA1c was 5%) the concentration of fasting C-peptide was 0.793±225 nmol/L (mean±SD) in subjects with normal glucose tolerance, 0.805+200 nmol/L in NDT and 0.807±231 nmol/L in IGT subjects (p=NS). Similarly, plasma concentrations of triglycerides and blood pressure values were similar when subjects of different categories were compared at the same level of glycemia. Sixteen normal subjects were rendered mildly hyperglycemic by a 24-h glucose infusion to match the fasting glucose level of NDT (1 mg/kg/min) and IGT (2 mg/kg/min) subjects. At the same fasting glucose level, normal subjects presented elevations of fasting C-peptide significantly (p<0.01) higher than subjects belonging to the NDT and IGT categories. In conclusion, overweight people with impaired glucose tolerance present beta-cell hyperfunction in the fasting state which, however, is largely inappropriate for the prevailing glucose level; in these persons, glucose intolerance per se is not associated with hyperinsulinemia.