Skin vasoreactivity to insulin iontophoresis is reduced in elderly subjects and is absent in treated non-insulin-dependent diabetes patients

Impact of a lifestyle program on vascular insulin resistance in metabolic syndrome subjects: the RESOLVE study

CONTEXT AND OBJECTIVE

Impaired insulin-dependent vasodilation might contribute to microvascular dysfunction of metabolic syndrome (MetS). The aims of this study were to assess the insulin vasoreactivity in MetS, and to evaluate the effects of a lifestyle program. DESIGN, SETTING, PARTICIPANTS, AND OUTCOME MEASURES: Laser Doppler measurements were used to assess cutaneous blood flux (CBF) and flowmotion in response to iontophoresis of insulin and acetylcholine (ACh) in 38 MetS and 18 controls. Anthropometric, plasma insulin, glycemia, and inflammatory markers were measured. MetS subjects (n = 24) underwent a 6-month lifestyle intervention (M6) with a 3-week residential program (D21).

RESULTS

The absolute and relative peak insulin and ACh CBF were significantly higher in controls than in MetS subjects. Significant inverse correlations were found between peak insulin CBF and glycemia, insulin and glycated hemoglobin, active plasminogen activator inhibitor-1 (PAI-1), C-reactive protein (CRP), and IL-6. With respect to flowmotion, MetS subjects showed lower values in total spectrum CBF and in all its components (except respiratory one). At D21 and M6, peak insulin CBF increased and was no longer different from control values whereas peak ACh CBF did not change. From D21, all the different components and the total CBF spectrum became similar to the control values. The changes in peak insulin CBF and in endothelial component between M6 and baseline were inversely correlated with the change in CRP and PAI-1.

CONCLUSIONS

The local vasodilatory effects to insulin and its overall flowmotion are impaired in MetS subjects in relation to inflammation. The lifestyle intervention reversed this insulin-induced vascular dysfunction in parallel to decreased inflammation level.

Premature aging of the microcirculation in patients with advanced chronic kidney disease

Background

Increasing age and advanced chronic kidney disease (CKD) are both associated with an attenuated vasodilator response of the skin microcirculation. In the present study, we investigated the effect of aging on microvascular reactivity in patients with advanced CKD.

Methods

Acetylcholine (ACh)-mediated endothelium-dependent vasodilation and sodium nitroprusside (SNP)-mediated endothelium-independent vasodilation were assessed by iontophoresis combined with laser Doppler flowmetry. Microvascular function was compared between 52 patients with advanced CKD (stage 4–5: n = 16; end-stage renal disease: n = 36) and 33 healthy control subjects. As aging has an important effect on microvascular function, both control subjects and CKD patients were divided in subgroups younger and older than 45 years. Linear regression analysis was applied to assess potential associations between microvascular function and various demographic and clinical parameters.

Results

There were three main findings. (1) In young patients with advanced CKD, both ACh- and SNP-mediated vasodilations were impaired if compared to young healthy controls (p = 0.04 and p = 0.056, respectively). (2) In young patients with advanced CKD, microvascular function was similar to old healthy controls and elderly patients with advanced CKD. (3) Whereas age was inversely associated with microvascular function in healthy controls (log ACh-mediated vasodilation R = −0.41; p = 0.02 and log SNP-mediated vasodilation R = −0.38; p = 0.03), no such relation was found in patients with advanced CKD.

Conclusions

Our results are consistent with premature aging of the microvascular vasodilatory capacity in patients with advanced CKD.

Small artery remodelling in diabetes

The aim of this article is to briefly review available data regarding changes in the structure of microvessels observed in patients with diabetes mellitus, and possible correction by effective treatment. The development of structural changes in the systemic vasculature is the end result of established hypertension. In essential hypertension, small arteries of smooth muscle cells are restructured around a smaller lumen and there is no net growth of the vascular wall, although in some secondary forms of hypertension, a hypertrophic remodelling may be detected. Moreover, in non-insulin-dependent diabetes mellitus a hypertrophic remodelling of subcutaneous small arteries is present. Indices of small resistance artery structure, such as the tunica media to internal lumen ratio, may have a strong prognostic significance in hypertensive and diabetic patients, over and above all other known cardiovascular risk factors. Therefore, regression of vascular alterations is an appealing goal of antihypertensive treatment. Different antihypertensive drugs seem to have different effect on vascular structure. In diabetic hypertensive patients, a significant regression of structural alterations of small resistance arteries with drugs blocking the renin–angiotensin system (angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers) was demonstrated. Alterations in the microcirculation represent a common pathological finding, and microangiopathy is one of the most important mechanisms involved in the development of organ damage as well as of clinical events in patients with diabetes mellitus. Renin–angiotensin system blockade seems to be effective in preventing/regressing alterations in microvascular structure.

Small artery remodeling in diabetes mellitus

AIMS

To briefly review available data regarding changes in the structure of microvessels observed in patients with diabetes mellitus, and possible correction by effective treatment.

DATA SYNTHESIS

The development of structural changes in the systemic vasculature is the end result of established hypertension. In essential hypertension, small arteries' smooth muscle cells are restructured around a smaller lumen and there is no net growth of the vascular wall, while in some secondary forms of hypertension, hypertrophic remodeling may be detected. Moreover, in non-insulin-dependent diabetes mellitus hypertrophic remodeling of subcutaneous small arteries is present. Indices of small resistance artery structure, such as the tunica media to internal lumen ratio, may have a strong prognostic significance in hypertensive and diabetic patients, over and above all other known cardiovascular risk factors. Therefore, regression of vascular alterations is an appealing goal of antihypertensive treatment. Different antihypertensive drugs seem to have different effects on vascular structure. In diabetic hypertensive patients, a significant regression of structural alterations to the small resistance arteries with drugs blocking the renin-angiotensin system (ACE inhibitors, angiotensin II receptor blockers) was demonstrated.

CONCLUSION

Alterations in the microcirculation represent a common pathological finding, and microangiopathy is one of the most important mechanisms involved in the development of organ damage as well as of clinical events in patients with diabetes mellitus. Renin-angiotensin system blockade seems to be effective in preventing and/or regressing alterations in the microvascular structure.

Impaired local microvascular vasodilatory effects of insulin and reduced skin microvascular vasomotion in obese women

Our study aim is to investigate whether obesity is characterized by an impairment of insulin-mediated vasodilatory effects and by a modification of basal vasomotion in the skin microvasculature. Forty healthy obese and forty healthy lean women were included. Microvascular effects of insulin as compared to a control substance were measured by cathodal iontophoresis combined with laser Doppler flowmetry. Vasomotion was examined by Fourier transform analyses of skin laser Doppler flow at rest. Locally administered insulin, as compared to the control substance, induced a microvascular vasodilatory response in lean (median (interquartile range): 31.6 (17.1-43.9) vs. 22.9 (16.4-36.7) perfusion units, P=0.04), but not in obese women (28.1 (14.4-47.1) vs. 27.5 (17.5-48.2) perfusion units, P=0.7). The relative insulin-induced increase in blood flow corrected for the control substance was higher in lean than obese women (ANOVA for repeated measures F=3.93, P=0.05). The contribution of the total frequency spectrum 0.01-1.6 Hz and of the frequency intervals 0.01-0.02 Hz and 0.02-0.06 Hz (representative of endothelial and neurogenic activity, respectively) to basal microvascular vasomotion was lower in obese than in lean women (P<0.05 for all). These findings show that obesity is characterized by an impaired direct microvascular vasodilatory effect of insulin and by decreased skin microvascular vasomotion in a way that is suggestive for alterations of endothelial and neurogenic activity.

Skin microcirculatory effect of exogenous calcitonin gene-related peptide (CGRP) evaluated by laser Doppler flowmetry coupled with iontophoresis in healthy subjects

The aim of our study was to evaluate the feasibility of laser Doppler flowmetry (LDF) coupled with iontophoresis in exploring the skin vasodilator activity of exogenous calcitonin gene-related peptide (CGRP) in healthy subjects and to investigate the mechanisms involved in the skin vasodilator activity of this peptide. Forearm skin blood perfusion was measured in conventional perfusion unit (PU; 1 PU=10 mV), using a LDF apparatus (Periflux PF4001, Perimed, Sweden), before and following exogenous CGRP dissolved in distilled water (0.02%) or pure saline iontophoresis. Different iontophoresis protocols were used in a preliminary dose finding study in six subjects. Two pulses (0.1 mA for 30 s each) of anodal CGRP or saline iontophoresis were used in the definitive study in 20 subjects. Power spectral density (PSD) of skin blood flowmotion frequency intervals (FI), related to endothelial (0.009-0.02 Hz), sympathetic (0.02-0.06 Hz), myogenic (0.06-0.2 Hz), respiratory (0.2-0.6 Hz) and heart (0.6-1.6 Hz) activities, was also measured in PU(2)/Hz, by means of spectral analysis of the skin LDF signal registered before and following iontophoresis of CGRP or saline in the definitive study. A significantly higher per cent increase in skin perfusion compared to baseline was observed following CGRP than saline iontophoresis (548+/-369% vs. 326+/-192%, p<0.05), with higher hyperaemic response to pure saline than CGRP iontophoresis in only five subjects. A significant increase (p<0.05) in PSD mean value of the five FI considered, was also observed following CGRP iontophoresis, while saline iontophoresis elicited a significant increase (p<0.05) only in PSD of the FI related to endothelial, respiratory and heart activity. These findings demonstrated that LDF coupled with iontophoresis is a feasible method in evaluating the vasodilator effect of exogenous CGRP in human skin and suggest that this peptide directly or indirectly induces a smooth muscle vascular cells and sympathetic fibres stimulation.

Cathodal current-induced vasodilation to single application and the amplified response to repeated application in humans rely on aspirin-sensitive mechanisms

Assumed to rely on an axon reflex, the current-induced vasodilation (CIV) interferes with the microvascular response to iontophoretic drug delivery. Mechanisms resulting in CIV are likely different at the anode and at the cathode. While studies have been conducted to understand anodal CIV, little information is available on cathodal CIV. The present study investigates CIV observed following 0.1-mA cathodal applications on forearms of healthy volunteers and the possible mechanisms involved. Results are expressed in percentage of the cutaneous heat-induced maximal vascular conductance [%MVC (means ± SE)]. 1) The amplitude of CIV was proportional to the duration of cathodal currents for periods of <1 min: r = 0.99. 2) Two current applications of 10 s, with 10-min interstimulation interval, induced a higher peak value of CIV (79.1 ± 8.6% MVC) than the one obtained with all-at-once 20-s current application (39.5 ± 4.3% MVC, P < 0.05). This amplified vascular response due to segmental application was observed for all tested interstimulation intervals (up to 40 min). 3) Two hours and 3 days following pretreatment with 1-g oral aspirin, the CIV observed following cathodal application, as well as the difference of cathodal CIV amplitude between all-at-once and segmented applications, were reduced. These findings suggest a role of prostaglandins, not only released from endothelial or smooth muscle cells, as direct vasodilator and/or as a sensitizer. Thus aspirin pretreatment could be used to decrease CIV resulting from all-at-once and repeated cathodal application and facilitate the study of the specific vascular effect induced by the drug delivered.