Background This investigation examined the mechanisms by which coronary perivascular adipose tissue (PVAT)-derived factors influence vasomotor tone and the PVAT proteome in lean vs. obese swine. Methods and Results Coronary arteries from Ossabaw swine were isolated for isometric tension studies. We found that coronary (P=0.03) and mesenteric (P=0.04), but not subcutaneous adipose tissue, augmented coronary contractions to KCl (20 mM). Inhibition of CaV1.2 channels with nifedipine (0.1 μM) or diltiazem (10 μM) abolished this effect. Coronary PVAT increased baseline tension and potentiated constriction of isolated arteries to PGF2α in proportion to the amount of PVAT present (0.1–1.0 g). These effects were elevated in tissues obtained from obese swine and were observed in intact and endothelium denuded arteries. Coronary PVAT also diminished H2O2-mediated vasodilation in lean, and to a lesser extent in obese arteries. These effects were associated with alterations in the obese coronary PVAT proteome (detected 186 alterations) and elevated voltage-dependent increases in intracellular [Ca2+] in obese smooth muscle cells. Further studies revealed that a Rho-kinase inhibitor fasudil (1 μM) significantly blunted artery contractions to KCl and PVAT in lean, but not obese swine. Calpastatin (10 μM) also augmented contractions to levels similar to that observed in the presence of PVAT. Conclusions Vascular effects of PVAT vary according to anatomic location and are influenced by an obese phenotype. Augmented contractile effects of obese coronary PVAT are related to alterations in the PVAT proteome (e.g. calpastatin), Rho-dependent signaling, and the functional contribution of K+ and CaV1.2 channels to smooth muscle tone.

The purpose of this investigation was to test the hypothesis that KV channels contribute to metabolic control of coronary blood flow and that decreases in KV channel function and/or expression significantly attenuate myocardial oxygen supply-demand balance in the metabolic syndrome (MetS). Experiments were conducted in conscious, chronically instrumented Ossabaw swine fed either a normal maintenance diet or an excess calorie atherogenic diet that produces the clinical phenotype of early MetS. Data were obtained under resting conditions and during graded treadmill exercise before and after inhibition of KV channels with 4-aminopyridine (4-AP, 0.3 mg/kg, i.v.). In lean-control swine, 4-AP reduced coronary blood flow ~15% at rest and ~20% during exercise. Inhibition of KV channels also increased aortic pressure (P < 0.01) while reducing coronary venous Po2 (P < 0.01) at a given level of myocardial oxygen consumption (MVo2). Administration of 4-AP had no effect on coronary blood flow, aortic pressure, or coronary venous Po2 in swine with MetS. The lack of response to 4-AP in MetS swine was associated with a ~20% reduction in coronary KV current (P < 0.01) and decreased expression of KV1.5 channels in coronary arteries (P < 0.01). Together, these data demonstrate that KV channels play an important role in balancing myocardial oxygen delivery with metabolism at rest and during exercise-induced increases in MVo2. Our findings also indicate that decreases in KV channel current and expression contribute to impaired control of coronary blood flow in the MetS.

Glucagon-Like Peptide 1 (GLP-1) has insulin-like effects on myocardial glucose uptake which may contribute to its beneficial effects in the setting of myocardial ischemia. Whether these effects are different in the setting of obesity or type 2 diabetes (T2DM) requires investigation. We examined the cardiometabolic actions of GLP-1 (7–36) in lean and obese/T2DM humans, and in lean and obese Ossabaw swine. GLP-1 significantly augmented myocardial glucose uptake under resting conditions in lean humans, but this effect was impaired in T2DM. This observation was confirmed and extended in swine, where GLP-1 effects to augment myocardial glucose uptake during exercise were seen in lean but not in obese swine. GLP-1 did not increase myocardial oxygen consumption or blood flow in humans or in swine. Impaired myocardial responsiveness to GLP-1 in obesity was not associated with any apparent alterations in myocardial or coronary GLP1-R expression. No evidence for GLP-1 mediated activation of cAMP/PKA or AMPK signaling in lean or obese hearts was observed. GLP-1 treatment augmented p38-MAPK activity in lean, but not obese cardiac tissue. Taken together, these data provide novel evidence indicating that the cardiometabolic effects of GLP-1 are attenuated in obesity and T2DM, via mechanisms that may involve impaired p38-MAPK signaling.

-Altered myocardial fuel selection likely underlies cardiac disease risk in diabetes, affecting oxygen demand and myocardial metabolic flexibility. We investigated myocardial fuel selection and metabolic flexibility in human type 2 diabetes mellitus (T2DM), using positron emission tomography to measure rates of myocardial fatty acid oxidation {16-[ 18 F]fluoro-4-thia-palmitate (FTP)} and myocardial perfusion and total oxidation ([ 11 C]acetate). Participants underwent paired studies under fasting conditions, comparing 3-h insulin ϩ glucose euglycemic clamp conditions (120 mU·m Ϫ2 ·min Ϫ1 ) to 3-h saline infusion. Lean controls (n ϭ 10) were compared with glycemically controlled volunteers with T2DM (n ϭ 8). Insulin augmented heart rate, blood pressure, and stroke index in both groups (all P Ͻ 0.01) and significantly increased myocardial oxygen consumption (P ϭ 0.04) and perfusion (P ϭ 0.01) in both groups. Insulin suppressed available nonesterified fatty acids (P Ͻ 0.0001), but fatty acid concentrations were higher in T2DM under both conditions (P Ͻ 0.001). Insulin-induced suppression of fatty acid oxidation was seen in both groups (P Ͻ 0.0001). However, fatty acid oxidation rates were higher under both conditions in T2DM (P ϭ 0.003). Myocardial work efficiency was lower in T2DM (P ϭ 0.006) and decreased in both groups with the insulin-induced increase in work and shift in fuel utilization (P ϭ 0.01). Augmented fatty acid oxidation is present under baseline and insulin-treated conditions in T2DM, with impaired insulin-induced shifts away from fatty acid oxidation. This is accompanied by reduced work efficiency, possibly due to greater oxygen consumption with fatty acid metabolism. These observations suggest that improved fatty acid suppression, or reductions in myocardial fatty acid uptake and retention, could be therapeutic targets to improve myocardial ischemia tolerance in T2DM. myocardial; heart; diabetes; metabolism; metabolic flexibility; positron emission tomography ALTERATIONS IN METABOLIC SUBSTRATE uptake and metabolism are part of the phenotype that defines type 2 diabetes mellitus (T2DM) (3,4,33,39,74). The phenomenon of "metabolic flexibility" is the capacity of an organism, a tissue bed, or a cell system to switch readily among fuel types. Impaired metabolic flexibility is another phenotypic feature of T2DM (33, 66).Impaired metabolic flexibility has been demonstrated in skeletal muscle in human diabetes (32,66). This whole body effect likely arises due to effects of impaired insulin-stimulated glucose uptake, together with abnormalities in availability, uptake, and metabolism of fatty acid fuels (33,66,75).The myocardium is also affected by T2DM. The fuel needs of the heart are dramatically different than those of skeletal muscle, supporting continuous work even under resting conditions. Abnormalities in myocardial fuel selection in animal models of diabetes have been described (42,54,75), including impairments in insulin-stimulated glucose uptake and impaired suppression of myocardial fatty acid u...

The mechanisms responsible for coronary pressure-flow autoregulation, a critical physiologic phenomenon that maintains coronary blood flow relatively constant in the presence of changes in perfusion pressure, remain poorly understood. This investigation tested the hypothesis that voltage-sensitive K+ (KV) and Ca2+ (CaV1.2) channels play a critical role in coronary pressure-flow autoregulation in vivo. Experiments were performed in open-chest, anesthetized Ossabaw swine during step changes in coronary perfusion pressure (CPP) from 40 to 140 mmHg before and during inhibition of KV channels with 4-aminopyridine (4AP, 0.3 mM, ic) or CaV1.2 channels with diltiazem (10 μg/min, ic). 4AP significantly decreased vasodilatory responses to H2O2 (0.3–10 μM, ic) and coronary flow at CPPs = 60–140 mmHg. This decrease in coronary flow was associated with diminished ventricular contractile function (dP/dT) and myocardial oxygen consumption. However, the overall sensitivity to changes in CPP from 60 to 100 mmHg (i.e. autoregulatory gain; Gc) was unaltered by 4-AP administration (Gc = 0.46 ± 0.11 control vs. 0.46 ± 0.06 4-AP). In contrast, inhibition of CaV1.2 channels progressively increased coronary blood flow at CPPs > 80 mmHg and substantially diminished coronary Gc to −0.20 ± 0.11 (P < 0.01), with no effect on contractile function or oxygen consumption. Taken together, these findings demonstrate that (1) KV channels tonically contribute to the control of microvascular resistance over a wide range of CPPs, but do not contribute to coronary responses to changes in pressure; (2) progressive activation of CaV1.2 channels with increases in CPP represents a critical mechanism of coronary pressure-flow autoregulation.

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Previous investigations indicate that diminished functional expression of voltage-dependent K+ (KV) channels impairs control of coronary blood flow in obesity/metabolic syndrome. The goal of this investigation was to test the hypothesis that KV channels are electromechanically coupled to CaV1.2 channels and that coronary microvascular dysfunction in obesity is related to subsequent increases in CaV1.2 channel activity. Initial studies revealed that inhibition of KV channels with 4-aminopyridine (4AP, 0.3 mM) increased intracellular [Ca2+], contracted isolated coronary arterioles and decreased coronary reactive hyperemia. These effects were reversed by blockade of CaV1.2 channels. Further studies in chronically instrumented Ossabaw swine showed that inhibition of CaV1.2 channels with nifedipine (10 μg/kg, iv) had no effect on coronary blood flow at rest or during exercise in lean swine. However, inhibition of CaV1.2 channels significantly increased coronary blood flow, conductance, and the balance between coronary flow and metabolism in obese swine (P < 0.05). These changes were associated with a ~50 % increase in inward CaV1.2 current and elevations in expression of the pore-forming subunit (α1c) of CaV1.2 channels in coronary smooth muscle cells from obese swine. Taken together, these findings indicate that electromechanical coupling between KV and CaV1.2 channels is involved in the regulation of coronary vasomotor tone and that increases in CaV1.2 channel activity contribute to coronary microvascular dysfunction in the setting of obesity.

We examined the acute dose-dependent effects of intracoronary glucagon-like peptide (GLP)-1 (7–36) on coronary vascular tone, cardiac contractile function and metabolism in normal and ischemic myocardium. Experiments were conducted in open chest, anesthetized dogs at coronary perfusion pressures (CPP) of 100 and 40 mmHg before and during intracoronary GLP-1 (7–36) infusion (10 pmol/L to 1 nmol/L). Isometric tension studies were also conducted in isolated coronary arteries. Cardiac and coronary expression of GLP-1 receptors (GLP-1R) was assessed by Western blot and immunohistochemical analysis. GLP-1R was present in the myocardium and the coronary vasculature. The tension of intact and endothelium-denuded coronary artery rings was unaffected by GLP-1. At normal perfusion pressure (100 mmHg), intracoronary GLP-1 (7–36) (targeting plasma concentration 10 pmol/L to 1 nmol/L) did not affect blood pressure, coronary blood flow or myocardial oxygen consumption (MVO2); however, there were modest reductions in cardiac output and stroke volume. In untreated control hearts, reducing CPP to 40 mmHg produced marked reductions in coronary blood flow (0.50 ±0.10 to 0.17 ±0.03 mL/min/g; P < 0.001) and MVO2 (27 ±2.3 to 15 ±2.7 μL O2/min/g; P < 0.001). At CPP = 40 mmHg, GLP-1 had no effect on coronary blood flow, MVO2 or regional shortening, but dose-dependently increased myocardial glucose uptake from 0.11±0.02 μmol/min/g at baseline to 0.17±0.04 μmol/min/g at 1 nmol/L GLP-1 (P < 0.001). These data indicate that acute, intracoronary administration of GLP-1 (7–36) preferentially augments glucose metabolism in ischemic myocardium, independent of effects on cardiac contractile function or coronary blood flow.