The effects of 7-hour local hyperglycaemia on forearm macro and microcirculatory blood flow and vascular reactivity in healthy man

Acute effect of various dosages of sugar ingestion on vascular function in offspring of hypertensive and normotensive parents

OBJECTIVES

We aimed to study vascular function in healthy men with a parental history of hypertension compared to those without. Acute effect of various dosages of sugar ingestion on vascular function was also investigated in both groups.

METHODS

Thirty-two healthy men were recruited and divided into two groups, offspring of hypertensive parents (OHT) and offspring of normotensive parents (ONT). Participants were orally given 15, 30, and 60 g of sucrose solution compared to water. Peak forearm blood flow (FBF), forearm vascular resistance (FVR), pulse wave velocity (PWV), and oxidative stress markers were measured at baseline and after sucrose intake at 30, 60, 90, and 120 min.

RESULTS

At baseline, peak FBF was significantly lower (22.40 ± 1.18 vs. 25.24 ± 0.63 ml × dl -1  × min -1 , P  < 0.001), FVR was significantly higher (3.73 ± 0.42 vs. 3.30 ± 0.26 mmHg × ml -1  × dl × min, P  = 0.002), and PWV was significantly faster (6.31 ± 0.59 vs. 5.78 ± 0.61 m/s, P  = 0.017) in OHT than ONT. After each sucrose intake, peak FBF significantly declined and was lowest at 30 min in both groups. The reduction in peak FBF was seen in all doses of sucrose and the higher dose of sucrose intervened, the longer reduction in peak FBF observed.

CONCLUSIONS

Vascular function was attenuated in healthy men with a family history of hypertension and became worse after sucrose ingestion even at the low dose. Our findings suggest that the ones, especially those with a parental history of hypertension, should reduce sugar consumption as low as possible.

Sexual dimorphism in rabbit aortic endothelial function under acute hyperglycemic conditions and gender-specific responses to acute 17beta-estradiol

Epidemiological data suggest that hyperglycemia abrogates the gender-based cardiovascular protection possibly associated with estrogens. This study was designed to investigate 1) whether rabbit aortic rings show gender differences in the development of abnormal endothelium-dependent vasodilation (EDV) under acute hyperglycemic conditions, 2) the potential role of PKC isoforms and superoxide (O2-) in acute hyperglycemia-induced vascular dysfunction, and 3) the effect of acute estrogen administration on hyperglycemia-induced endothelial dysfunction in male and female rabbits. EDV to ACh was determined before and after 3 h of treatment with high glucose (HG) in phenylephrine-precontracted aortic rings from male and female New Zealand White rabbits. Similar experiments were conducted in the presence of inhibitors of PKC-alpha, PKC-beta, and PKC-delta or an O2- scavenger. The effect of acute estrogen administration was evaluated in the presence and absence of HG. Finally, mRNA expression of PKC isoforms was measured by real-time PCR. We found that 1) 3 h of incubation with HG impairs EDV to a greater extent in female than male aorta, 2) inhibition of PKC-beta or O2- prevents HG-induced impairment of EDV in female aorta, 3) acute 17beta-estradiol aggravates HG-induced endothelial dysfunction in female, but not male, aorta, and 4) PKC-alpha and PKC-beta expression are significantly higher in female than male aorta. This study reveals the predisposition of female rabbit aorta to vascular injury under hyperglycemic conditions, possibly via activation of PKC-beta and O2- production. Furthermore, it suggests that, under hyperglycemic conditions, acute estrogen treatment is detrimental to endothelial function in female rabbits.

Microvascular abnormalities in chronic heart failure: a cross-sectional analysis

OBJECTIVES

Similar to what has been found in hypertension, elevated peripheral resistance in chronic heart failure (CHF) might be related to microvascular constriction and rarefaction. Our objective was to evaluate both structural and functional microvascular changes in patients with CHF in relation to left ventricular function and neurohumoral activation.

METHODS

In 25 patients with mild and severe CHF (New York Heart Association class I-II [n = 11] and class III-IV [n = 14]) and 10 age-matched healthy subjects, we studied microvascular density, diameters, and morphology of the bulbar conjunctiva and skin nailfold using intravital microscopy.

RESULTS

Total conjunctival microvascular density was higher in patients with mild heart failure compared with healthy controls, whereas it was lower in severe heart failure (medians, 6.75, 4.31, and 3.56 mm/mm2, respectively, p < 0.01). In patients with heart failure, venular density was correlated with left ventricular ejection fraction. Nailfold capillary recruitment during postocclusive reactive hyperemia, a measure of functional reserve capacity, was impaired in patients with severe CHF (p < 0.05). Furthermore, in severe CHF, more abnormal capillaries and enlarged diameters were found in the nailfold (p < 0.05).

CONCLUSIONS

In heart failure, several microvascular abnormalities occur that differ, depending on the severity of this condition.

Doppler sonographic characteristics of umbilical and uterine arteries during oral glucose tolerance testing in healthy pregnant women

PURPOSE

Studies have shown that maternal hyperglycemia may be associated with increased placental resistance to blood flow and possibly adverse perinatal outcomes. The aim of this study was to determine whether Doppler velocimetric dynamics change in the uterine and umbilical arteries in healthy pregnant women (without gestational diabetes) during acute hyperglycemia induced by oral glucose tolerance testing.

METHODS

Flow in the umbilical and right and left uterine arteries was assessed by spectral Doppler sonographic examination of healthy pregnant women at 24-28 weeks' menstrual age. Four Doppler studies were conducted for each woman: 1 before oral administration of 100 g of glucose and 3 more at 1, 2, and 3 hours after glucose administration. The systolic-to-diastolic ratio was calculated for the umbilical artery, and the resistance index was calculated separately for the left and right uterine arteries.

RESULTS

All results of oral glucose tolerance testing were normal, and Doppler signals were obtained in all 30 patients enrolled. No abnormal systolic-to-diastolic ratios or resistance indices were detected in any of the examinations. No significant differences in waveforms or resistance indices between the right and left uterine arteries were found during the various testing intervals.

CONCLUSIONS

Acute hyperglycemia induced in healthy pregnant women does not affect blood flow velocimetric characteristics in the umbilical or uterine arteries at any stage of oral glucose tolerance testing.

Inhibition of protein kinase Cbeta prevents impaired endothelium-dependent vasodilation caused by hyperglycemia in humans

The bioavailability of nitric oxide is decreased in animal models and humans with diabetes mellitus. Hyperglycemia, in particular, attenuates endothelium-dependent vasodilation in healthy subjects. In vitro and in vivo animal studies implicate activation of protein kinase Cbeta as an important mechanism whereby hyperglycemia decreases endothelium-derived nitric oxide. Accordingly, this study tested the hypothesis that inhibition of protein kinase Cbeta would prevent impairment of endothelium-dependent vasodilation in healthy humans exposed to hyperglycemia. This study was a randomized, double-blind, placebo-controlled, crossover trial. Healthy subjects were treated with an orally active, selective, protein kinase Cbeta inhibitor, LY333531, or matching placebo once a day for 7 days before vascular function testing. Forearm blood flow was measured using venous-occlusion, strain-gauge plethysmography. Endothelium-dependent vasodilation was measured via incremental brachial artery administration of methacholine chloride (0.3 to 10 microg/min) during euglycemia and after 6 hours of hyperglycemic clamp. The forearm blood flow dose-response curve to methacholine was significantly attenuated by hyperglycemia after placebo treatment (P=0.009 by ANOVA, euglycemia versus hyperglycemia) but not after treatment with LY333531. Inhibition of protein kinase Cbeta prevents the reduction in endothelium-dependent vasodilation induced by acute hyperglycemia in healthy humans in vivo. These findings suggest that hyperglycemia impairs endothelial function, in part, via protein kinase Cbeta activation.

Additive effect of coexistent type 2 diabetes and arterial hypertension on endothelial dysfunction in resistance arteries of human forearm vasculature

Population studies suggest that vascular complications accumulate when arterial hypertension supervenes on diabetes mellitus. Although it has been demonstrated that endothelial function is impaired in patients with either diabetes mellitus or arterial hypertension it is unknown whether or not both diseases exert additive effects on endothelial dysfunction. The authors therefore investigated endothelium-dependent and endothelium-independent vasodilation in the forearm vasculature of 44 individuals: in 10 type 2 diabetic patients (DM), in 12 patients with arterial hypertension (HT), in 10 patients with both DM and HT (DM+HT), and in 12 healthy control subjects (C). Forearm blood flow (FBF) was measured by venous occlusion plethysmography at rest and following intraarterial infusion of acetylcholine (ACh) and the NO-donor sodium nitroprusside (SNP) at increasing doses. FBF at rest was significantly lower in diabetic patients: 2.2 +/- 0.1 (DM) and 2.6 +/- 0.2 (DM+HT) versus 3.1 +/- 0.1 (HT) and 3.4 +/- 0.2 (C) mL/min per 100 mL of tissue. ACh and SNP both increased FBF dose-dependently in each group. The maximum response to ACh was progressively decreased in DM and HT: 13.7 (C) > 8.1 (DM) > 7.6 (HT) > and 5.7 (DM+HT) mL/min per 100 mL of tissue. Reduction of the endothelium-dependent flow reserve assessed as percent increase in maximum FBF was also impaired following the same rank order: 349 (C) > 268 (DM) > 160 (HT) > 126 (DM+HT)%. The flow response to the NO-donor SNP amounted to: 327 (C), 306 (DM), 200 (HT), and 194% (DM+HT). In DM+HT the reduction of endothelium-dependent flow response was more pronounced compared with the endothelium-independent flow response. The present data provide evidence that type 2 diabetes and arterial hypertension impair endothelium-dependent dilation of resistance arteries in an additive manner suggesting that this progressive endothelial dysfunction might contribute to the increased incidence of cardiovascular complications when both diseases are coexistent.

Hand vein responses to noradrenaline in normotensive patients with insulin-dependent diabetes mellitus and microalbuminuria: effects of alpha-adrenoceptor blockade with doxazosin

Nephropathy commonly develops in patients with insulin-dependent (type 1) diabetes. Administration of an antihypertensive agent to type 1 diabetes patients with microalbuminuria, the first clinically detectable stage of nephropathy, can help slow renal deterioration. It is postulated that the exaggerated vasoconstrictor response to noradrenaline seen in these patients may be relevant in the development of microalbuminuria. This open, non-comparative pilot study was designed to investigate the effects of the alpha-adrenoceptor antagonist doxazosin on noradrenaline-induced hand vein vasoconstriction and on albumin excretion in 14 normotensive type 1 diabetes patients with microalbuminuria. After a three-week placebo run-in period, patients received doxazosin (1, 2, and then 4 mg once-daily, at two-week intervals) for six weeks, followed by a two-week placebo washout period. Vasoconstrictor responses to noradrenaline were measured in dorsal hand veins at the end of each two-week period. Hand vein vasoconstrictor responses to noradrenaline decreased significantly, compared with placebo, at 4 mg/day doxazosin (p = 0.006). The mean albumin excretion rate was lower than baseline at all doses of doxazosin, but changes did not reach statistical significance. Doxazosin was generally well-tolerated; four patients (29%) reported mild-to-moderate treatment-related adverse events. This study indicates that alpha 1-adrenoceptor blockade can blunt the exaggerated vascular reactivity to noradrenaline in normotensive type 1 diabetes patients with microalbuminuria, and supports further research into a potential role for doxazosin in preventing the development of diabetic nephropathy.

The acute effect of hyperglycaemia on vessel wall properties

Arterial distensibility is a marker of functional and structural vessel wall properties. A decreased distensibility is an important risk factor for cardiovascular disease. In insulin-dependent diabetes mellitus of short duration, arterial stiffness has been reported to be increased, decreased or the same as in healthy control subjects. The influence of acute hyperglycaemia on arterial stiffness is unclear and might be one of the factors responsible for the divergent results which have been observed. We investigated arterial distensibility locally in the carotid artery during hyper- and normoglycaemia using a glucose clamp technique. Eleven healthy normotensive men underwent both a hyperglycaemic and a euglycaemic clamp on separate days. Before and after 2 h of clamping, arterial diameter (D) and change in arterial diameter during the heart cycle (dD) were measured with a non-invasive vessel wall movement detector system. Blood pressure (BP), pulse pressure (dP) and heart rate (HR) were recorded with a semi-automated device. Distensibility coefficients (DC), reflecting the intrinsic vascular wall elasticity, and compliance coefficients (CC), reflecting the buffering capacity of the vessel, were calculated from D, dD and dP. (DC = 2*dD/ D*dP, CC = pi*dD*D/2*dP). There were no significant differences between the hyperglycaemic and the euglycaemic clamp for D, DC and CC. These results suggest that an acute systemic hyperglycaemia is not responsible for changes in diameter, distensibility and compliance of the carotid artery.

Glutathione reverses systemic hemodynamic changes induced by acute hyperglycemia in healthy subjects

The present study aimed at evaluating whether acute elevations of plasma glucose concentrations could influence systemic hemodynamic parameters and baroreflex activity in humans. Plasma glucose concentrations were acutely raised to 15 mmol/l in 12 healthy male volunteers. During hyperglycemia, there were significant increments of systolic [from 118 +/- 9 to 138 +/- 12 (SD) mmHg, P < 0.01] and diastolic (from 71 +/- 5 to 85 +/- 6 mmHg, P < 0.001) blood pressure, as well as heart rate (from 76 +/- 7 to 85 +/- 10 beats/min, P < 0.01) and plasma catecholamine levels. Both maximal and steady-state mean arterial pressure after squatting were higher during hyperglycemia (27 +/- 8 and 16 +/- 6 mmHg, respectively) compared with levels obtained during euglycemia (18 +/- 5 and 2 +/- 0.6 mmHg, respectively, P < 0.001). The infusion of the somatostatin analogue octreotide (25 micrograms as i.v. bolus followed by a 0.5 microgram/min infusion), to avoid the possible confounding vascular actions of insulin, did not influence the hemodynamic effects of hyperglycemia except for a lesser increase of both heart rate and plasma catecholamines. Glutathione (600 mg as an iv bolus followed by a 5 mg/min infusion) completely prevented the vascular effects of hyperglycemia. This study shows that acute hyperglycemia, similar to that observed in poorly controlled diabetic patients, produces relevant systemic hemodynamic changes and also alters baroreflex activity via a glutathione-sensitive presumably free radical-mediated pathway.