S. Taddei

Effects of Insulin on Hemodynamics and Metabolism in Human Forearm

We investigated the vascular response (blood flow and resting vascular resistance) and the metabolic response (exchange of metabolites and respiratory gases) to local insulin administration in the forearms of healthy young volunteers with the use of the perfused-forearm technique. In the postabsorptive state, the deep tissues of the forearm (mostly skeletal muscle) took up glucose (mean +/- SE 1.09 +/- 0.17 mumol.min-1.dl-1 forearm vol), beta-hydroxybutyrate (0.267 +/- 0.130 mumol.min-1.dl-1), and O2 (9.96 +/- 1.02 mumol.min-1.dl-1) and released lactate (0.284 +/- 0.098 mumol.min-1.dl-1), glycerol (0.029 +/- 0.012 mumol.min-1.dl-1), citrate (0.091 +/- 0.030 mumol.min-1.dl-1), alanine (0.184 +/- 0.044 mumol.min-1.dl-1), CO2 (7.36 +/- 0.97 mumol.min-1.dl-1), and protons (12.1 +/- 1.4 pmol.min-1.dl-1). Forearm blood flow (by venous occlusion plethysmography) was 2.95 +/- 0.18 ml.min-1.dl-1, and intra-arterial systolic/diastolic blood pressure was 116 +/- 3/76 +/- 2 mmHg. Local indirect calorimetry indicated dominance of fat as the oxidative substrate (RQ 0.76 +/- 0.09) and an energy expenditure rate of 1.03 +/- 0.11 cal.min-1.dl-1 forearm vol. One hundred minutes of intra-arterial insulin infusion (deep venous plasma insulin concn of 125 +/- 11 microU/ml) had no detectable effect on forearm blood flow, resting forearm vascular resistance, heart rate, or blood pressure. Local hyperinsulinemia significantly stimulated glucose uptake (to 4.79 +/- 0.61 mumol.min-1.dl-1 forearm vol, P less than 0.001), lactate and pyruvate release (to 0.710 +/- 0.093 and 0.032 +/- 0.016 mumol.min-1.dl-1 forearm vol, respectively; P less than 0.01 for both), potassium uptake (0.76 +/- 0.22 mueq.min-1.dl-1, P less than 0.001), and free fatty acid uptake (0.123 +/- 0.041 mumol.min-1.dl-1 forearm vol, P less than 0.05); glycerol balance switched to a net uptake (P less than 0.001), alanine release was restrained by 33% (P less than 0.05), and beta-hydroxybutyrate and citrate release were unchanged. Despite these metabolic changes, local rates of substrate oxidation and energy expenditure were not altered by insulin. In contrast, forearm proton release was significantly stimulated by insulin (to 14.8 +/- 1.4 pmol.min-1.dl-1, P less than 0.02). Proton release was also found to be directly related to resting forearm vascular resistance independent of the effect of insulin (multiple r = 0.64, P less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

Myocardial Ultrasonic Backscatter in Hypertension Relation to Aldosterone and Endothelin

Abstract—A disproportionate accumulation of fibrillar collagen is a characteristic feature of hypertensive heart disease, but the extent of myocardial fibrosis may differ in different models of hypertension. In experimental studies, aldosterone and endothelins emerge as important determinants of myocardial fibrosis. Changes in myocardial extracellular matrix and collagen deposition can be estimated noninvasively by analysis of the ultrasonic backscatter signal, which arises from tissue heterogeneity within the myocardium and describes myocardial texture. This study was designed to investigate the relations between myocardial integrated backscatter and circulating aldosterone and immunoreactive endothelin in human hypertension. The study population consisted of 56 subjects: 14 healthy normotensive volunteers and 42 hypertensive patients (14 with primary aldosteronism, 7 with renovascular hypertension, and 21 with essential hypertension). The patients with essential and secondary hypertension were matched for age, gender, body mass index, and blood pressure. Myocardial integrated backscatter at diastole was 19.8±2.0 and 20.8±2.9 decibels in normotensive control subjects and patients with essential hypertension and significantly higher in patients with primary aldosteronism (27.4±3.8 decibels, P <0.01) and renovascular hypertension (26.8±4.8 decibels, P <0.01). In the population as a whole, as well as in the hypertensive subpopulation, myocardial integrated backscatter was directly related to plasma aldosterone (r =0.73 and 0.71, P <0.01 for both) and immunoreactive endothelin (r =0.60 and 0.56, P <0.01 for both). The data of this study suggest that in human hypertension, circulating aldosterone and immunoreactive endothelin may induce alterations in left ventricular myocardial texture, possibly related to increased myocardial collagen content.

6D.02: GHRELIN RESTORES NITRIC OXIDE AVAILABILITY IN THE FOREARM MICROCIRCULATION OF ESSENTIAL HYPERTENSIVE PATIENTS.

Objective: Essential hypertensive patients (EH) are characterized by endothelial dysfunction caused by a reduced nitric oxide (NO) availability due to reactive oxygen species excess and low-grade inflammatory condition. Ghrelin is a recently identified growth hormone-releasing peptide, with recognized cardiovascular actions. Possible effects on endothelial dysfunction have been never investigated in EH. In this study we evaluated whether exogenous ghrelin can improve endothelial dysfunction in the forearm microcirculation of untreated mild-moderate EH. Design and method: In 9 EH (51.8 ± 8.1 yrs) and 9 normotensive subjects (NS, 50.5 ± 3.5 yrs), we studied the forearm blood flow (FBF, strain-gauge plethysmography) response to intrabrachial acetylcholine (ACh, 0.15–15 mg/100 ml/min) with and without NO synthase blockade by L-NMMA (100 &mgr;g/100 ml/min), or the antioxidant vitamin (Vit) C (8 mg/100 ml/min). The protocol was repeated under exogenous ghrelin intra-arterial infusion (200 ng/min, 30’ pre-infusion). Results: In NS, the maximal vasodilation (VD) to ACh (480 ± 20%) was inhibited by L-NMMA (292 ± 22, -39 ± 7%; P < 0.001) and unchanged by Vit C (482 ± 34%). Ghrelin failed to modify these vascular responses. In EH, VD to ACh was blunted vs NS (337 ± 45%; P < 0.001) and resistant to L-NMMA (313 ± 32, -7 ± 3%). Vit C increased the response to ACh (509 ± 57%; P < 0.01 vs ACh alone) and restored the inhibiting effect of L-NMMA (332 ± 42, -34 ± 8%; P < 0.001). Ghrelin, while not modifying the basal FBF, it increased (P < 0.001) the VD to ACh (448 ± 55) and restored the inhibitory effect of L-NMMA on ACh (355 ± 43, -20 ± 6%; P < 0.001). Vit C only slightly improved VD to ACh under ghrelin infusion (486 ± 45%). In EH ghrelin significantly (P < 0.05) decreased plasma venous malodialdehyde (from 6.9 ± 1.5 to 5.2 ± 1.0 &mgr;mol/L), lipoperoxides (from 9.1 ± 1.9 to 6.6 ± 2.3 &mgr;mol/L) and IL-6 (from 11.1 ± 0.6 to 9.3 ± 1.0 pg/mL) and increased plasma antioxidant capacity (from 407 ± 109 to 630 ± 97 mmol/L). Response to sodium nitroprusside was similar between EH and NS and not affected by ghrelin. Conclusions: Exogenous ghrelin is able to increase endothelial dysfunction by restoring NO availability in the forearm microcirculation of EH, an effect probably determined by antioxidant and/or anti-inflammatory activities.

CORRELATION BETWEEN DIFFERENT MEASURES OF CARDIOVASCULAR AUTONOMIC REGULATION IN ESSENTIAL HYPERTENSION: PP.32.262

Objective: It is well established that essential hypertension is characterized by increased adrenergic tone in different districts. Aim of the study is to examine the correlation between different measures of cardiovascular autonomic regulation, muscle sympathetic nerve activity (MSNA) and spectral analysis of RR interval variability, and their possible relation with plasma markers of renin-angiotensin system and endothelin activity. Design and Methods: 35 untreated essential hypertensive patients (HT) and 14 normotensive subjects (NT), age-and gender-matched, were included. MSNA was recorded by microneurography of the peroneal nerve, together with beat-to-beat BP and ECG for heart rate (HR) evaluation. Fast Fourier Transform spectral analysis of RR interval variability was applied to obtain normalized high and low frequency (nHF and nLF respectively) power density, and their ratio. Plasma norepinephrine (NE), renin activity (PRA) and endothelin-1 (ET-1) were also measured. Log-transformation was applied for correlation of not normally distributed variables. Results: HT showed higher MSNA (51.5 vs 41.4 bursts/100 heart beats, p < 0.001), NE (342 vs 269 pg/ml, p = 0.03), and LF/HF (3.4 vs 1.9, p = 0.04) as compared to NT. MSNA and LF/HF showed a significant correlation in the HT group (r = 0.36,p = 0.04), but not in the NT group (r = 0.20,p = ns). MSNA was also inversely related to nHF (r = -0.48,p = 0.004) in HT. MSNA and LF/HF were not significantly related to HR or NE in both HT and NT groups. In HT patients, but not in NT, nLF was related to NE (r = 0.43,p = 0.03) and ET-1 (r = -0.69,p = 0.01), while LF/HF was related to ET-1 (r = -0.70,p = 0.02). MSNA was not related to any of these humoral parameters in HT and NT. Conclusions: MSNA increase and sympatho-vagal unbalance in HR modulation are associated in essential hypertension. Spectral components of RR interval variability, but not MSNA, seem to be influenced by endothelin system in HT.

ROSUVASTATIN IMPROVES VASCULAR CHANGES AND OXIDATIVE STRESS IN ANGIOTENSIN II-INFUSED RATS: 1D.04

Objective: Angiotensin (Ang) II is involved in the development of vascular remodelling and reduced nitric oxide (NO) availability due to oxidant excess. An increased COX-1 activity contributes to Ang II-induced endothelial dysfunction. Statins exert beneficial vascular effects independently of their lipid lowering action. We assessed the effects of rosuvastatin (rosu) on vascular remodeling and endothelial dysfunction of small mesenteric arteries from Ang II-treated rats. Methods: Male Sprague Dawley rats, which received vehicle or Ang II (120 ng/kg/min by subcutaneous osmotic minipumps), were treated with rosu for 2 weeks (10 mg/Kg/day, by intragastric route). Vascular function and structure were studied on pressurized myograph. Plasma total cholesterol and malondialdehyde (MDA) were also assayed. Results: Ang II-rats showed an increased media/lumen vs controls (M/L: 7.1 ± 0.4% vs 4.8 ± 0.2; p < 0.05), with normal media cross sectional area (MCSA: 12.8 ± 1.1 vs 10.3 ± 0.3 μm2 × 103), an alteration partly prevented by Rosu (M/L: 6.5 ± 0.6%; MCSA: 12.9 ± 0.9 μm2 x 103). In controls, relaxation to acetylcholine (Ach, 97.5 ± 0.7%) was blunted by L-NAME (52.4 ± 0.4%; p < 0.05), whereas SC-560 or DFU, selective COX-1 and COX-2 inhibitors respectively, were ineffective. Ascorbic acid (Asc. Ac.) failed to affect the response to Ach. In Ang II group, the blunted response to Ach (57.5 ± 0.4%; p < 0.05 vs controls) was slightly affected by L-NAME (45.5 ± 3.9%) and improved by SC-560 (81.4 ± 0.6%; p < 0.05), while DFU was ineffective. Asc. Ac. ameliorated ACh-induced relaxation (93.4 ± 1.2%) and restored the inhibition by L-NAME (57.1 ± 2.3%). Rosu normalized the relaxation to Ach (96.3 ± 1.3%) and restored the inhibition by L-NAME (55.6 ± 2.1%). COX-1, COX-2 inhibitors and Asc. Ac. became ineffective on relaxation to ACh. Plasma MDA was increased by Ang II (22.8 ± 2.1 vs 12.6 ± 2.4 ìM) and normalized by rosu (13.4 ± 1.8 μM). Rosu also reduced (p < 0.05) plasma cholesterol (61.4 ± 6.1 vs 79.2 ± 5.5 mg/dL). Conclusions: Rosuvastatin ameliorates Ang II-induced vascular eutrophic remodeling and endothelial dysfunction in small resistance arteries. This beneficial effect is exerted through an abrogation of oxidative stress, a restoration of NO availability, and a reduction of COX-1-dependent contracting activity.

RESISTANCE ARTERY MECHANICS AND COMPOSITION IN ANGIOTENSIN II-INFUSED MICE: EFFECTS OF CYCLOOXYGENASE-1 INHIBITION: PP.6.229

Objective: Angiotensin (Ang) II is implicated in the development of vascular remodeling at the level of small resistance arteries, which include changes in the mechanical properties of arteries and vascular fibrosis due to an enhanced collagen and fibronectin contents. An increased intravascular expression/activity of cyclooxygenase (COX)-1 participates in Ang II-induced endothelial dysfunction. We investigated the contribution of COX-1 to vascular alterations in structure, mechanics and collagen deposition in mesenteric arteries from Ang II-treated mice. Methods: Male mice received vehicle or Ang II (400 ng/kg/min, s.c.) ± SC-560 (COX-1 inhibitor, 10 mg/Kg/day i.p.) or celecoxib (cele, COX-2 inhibitor, 400 mg/Kg/day, food) (2 weeks, n = 7 each). Mesenteric vessels, studied on pressurized myograph, were exposed to intraluminal pressures (3-140 mmHg). Media thickness and lumen diameter were measured to determine mechanical properties. Collagen type I was evaluated by immunohistochemistry. Results: Systolic blood pressure, increased by Ang II (162 ± 8 vs 108 ± 2 mmHg; P < 0.001), was slightly reduced by COX-1 antagonist (152 ± 6 mmHg) and unaffected by COX-2 (161 ± 6 mmHg). Media/lumen ratio, increased by Ang II (7.4 ± 0.1 vs 5.4 ± 0.1 %; P < 0.001), was partially reduced by COX-1 (6.0 ± 0.1%) and not modified by COX-2 inhibition (6.9 ± 0.1 %). Similarly, media cross-sectional area (103 x μm2) was increased by Ang II (9.5 ± 0.3 vs 7.5 ± 0.2; P < 0.001), partially reduced by COX-1 (8.4 ± 0.2; P < 0.01 vs Ang II group) and unaffected by COX-2 inhibition (9.1 ± 0.1). Ang II-treated group showed stiffer vessels, with leftward shift of the stress-strain relationship and a raised slope of the incremental elastic modulus-stress relationship as compared to controls (P < 0.01). This was attenuated (P < 0.05) by COX-1 inhibitor and unchanged by COX-2 blockade. The enhanced collagen deposition induced by Ang II (collagen/total area %: 12.6 ± 1.4 vs 3.1 ± 0.4; P < 0.001) was prevented by COX-1 (7.2 ± 1.1) but only slightly reduced by COX-2 inhibitor (9.8 ± 0.9). Conclusions: Ang II-induced vascular alterations in structure, mechanics and composition were partially prevented by SC-560 treatment, providing some evidence that some actions of Ang II on resistance arteries are mediated by COX-1 isoenzyme.