Modification of high saturated fat diet with n-3 polyunsaturated fat improves glucose intolerance and vascular dysfunction.

AIMS: The ability of dietary enrichment with monounsaturated fatty acid (MUFA), n-3 or n-6 polyunsaturated fatty acids (PUFAs) to reverse glucose intolerance and vascular dysfunction resulting from excessive dietary saturated fatty acids is not resolved. We hypothesized that partial replacement of dietary saturated fats with n-3 PUFA-enriched menhaden oil (MO) would provide greater improvement in glucose tolerance and vascular function compared to n-6 enriched safflower oil (SO) or MUFA-enriched olive oil (OO). METHODS: We fed mice a high saturated fat diet (HF) (60% kcal from lard) for 12 weeks before substituting half the lard with MO, SO or OO for an additional 4 weeks. At the end of 4 weeks, we assessed glucose tolerance, insulin signalling and reactivity of isolated pressurized gracilis arteries. RESULTS: After 12 weeks of saturated fat diet, body weights were elevated and glucose tolerance was abnormal compared to mice on control diet (13% kcal lard). Diet substituted with MO restored basal glucose levels, glucose tolerance and indices of insulin signalling (phosphorylated Akt) to normal, whereas restoration was limited for SO and OO substitutions. Although dilation to acetylcholine was reduced in arteries from mice on HF, OO and SO diets compared to normal diet, dilation to acetylcholine was fully restored and constriction to phenylephrine was reduced in MO-fed mice compared to normal. CONCLUSION: We conclude that short-term enrichment of an ongoing high fat diet with n-3 PUFA rich MO, but not MUFA rich OO or n-6 PUFA rich SO, reverses glucose tolerance, insulin signalling and vascular dysfunction.

Treatment of Zucker diabetic fatty rats with AVE7688 improves vascular and neural dysfunction.

AIM: Vasopeptidase inhibitors are drugs that inhibit angiotensin-converting enzyme and neutral endopeptidase (NEP). The latter is a protease that degrades vasoactive peptides and is increased in diabetes. We have previously shown that treating streptozotocin-induced diabetic rats, an animal model of type 1 diabetes, with AVE7688, a vasopeptidase inhibitor, improves neurovascular and neural function. In this study, we determined the effect of treating Zucker diabetic fatty (ZDF) rats, an animal model of type 2 diabetes, with AVE7688 on vascular and neural function. METHODS: ZDF rats at 12 weeks of age were treated for 12 weeks with AVE7688 (500 mg/kg diet). Afterwards, vascular reactivity of epineurial arterioles of the sciatic nerve and nerve conduction velocity and blood flow was determined. RESULTS: Vascular and neural function was significantly impaired in ZDF rats compared with age-matched lean (control) rats. Treating ZDF rats with AVE7688 improved vascular relaxation to acetylcholine and calcitonin gene-related peptide in epineurial arterioles. Motor and sensory nerve conduction velocity, endoneurial blood flow and thermal nociception end-points were also improved by treatment compared with untreated ZDF rats. Superoxide and expression of NEP were increased in epineurial arterioles from ZDF rats and attenuated by treatment with AVE7688. CONCLUSIONS: AVE7688 is an effective treatment for microvascular and neural disease in ZDF rats. Thus, vasopeptidase inhibitors may be an effective treatment for diabetic microvascular and neural complication in type 2 diabetes.

Vascular and neural dysfunction in Zucker diabetic fatty rats: a difficult condition to reverse.

AIM: We had previously demonstrated that vascular and neural dysfunction in Zucker diabetic fatty (ZDF) rats is progressive. In this study, we sought to determine whether monotherapy of ZDF rats can reverse the vascular and nerve defects. METHODS: ZDF rats at 16 weeks of age were treated for 12 weeks with the angiotensin-converting enzyme inhibitor enalapril, the antioxidant alpha-lipoic acid, the HMG-CoA reductase inhibitor rosuvastatin or the PPARgamma agonist rosiglitazone. Vasodilation of epineurial arterioles was measured by videomicroscopy. Endoneurial blood flow (EBF) was measured by hydrogen clearance, and nerve conduction velocity was measured following electrical stimulation of motor or sensory nerves. RESULTS: Motor nerve conduction velocity (MNCV), sensory nerve conduction velocity (SNCV) (70 and 77% of control, respectively), EBF (64% of control), and vascular relaxation in response to acetylcholine (50% of control) and calcitonin gene-related peptide (CGRP; 73% of control) are impaired in ZDF rats at 28 weeks of age compared with lean littermate controls. Treatment with enalapril and alpha-lipoic acid attenuated the decrease in MNCV and SNCV. Enalapril, alpha-lipoic acid and rosiglitazone treatment of ZDF rats were partially effective in improving endothelium-dependent vascular dysfunction as measured by vascular relaxation in response to acetylcholine. The same drugs also attenuated the decrease in EBF. However, impairment in vascular relaxation in response to CGRP was improved with only alpha-lipoic acid or rosuvastatin treatment. The increase in superoxide and nitrotyrosine levels in vascular tissue was attenuated by all treatments. CONCLUSIONS: The efficacy of monotherapy treatment of ZDF rats using different classes of drugs for vascular and neural dysfunction once complications have developed did not achieve expected levels. This could be because of the complex aetiology of vascular and neural disease in type 2 diabetes.

Effects of glycosylated hemoglobin on vascular responses in vitro.

UNLABELLED: Vascular responses to endothelium-dependent vasodilators are greatly impaired in vivo, while isolated blood vessels from animals with diabetes mellitus demonstrate less consistent degrees of impairment. Glycation of proteins, such as hemoglobin, has been implicated in the vascular abnormalities associated with diabetes. OBJECTIVE: The purpose of this study was to test the hypothesis that glycosylated hemoglobin is capable of reducing endothelium-dependent vasodilator responses, possibly explaining impaired dilation observed in vivo. METHODS: To test this hypothesis, the effect of glycosylated hemoglobin (GH) on vascular responses was studied in several vascular beds, including ventricular microvessels and coronary, mesenteric, femoral, and renal arteries. Coronary arterioles were isolated and mounted between two glass pipettes in a pressurized (30 cmH2O) organ chamber. Isolated artery segments were studied using a standard isometric ring technique. RESULTS: In ventricular microvessels, 10 nM nGH (non-GH) and GH both attenuated the relaxation to Ach. A lower concentration, 1 nM nGH or GH, did not alter dilation to Ach. In coronary, femoral, mesenteric and renal artery segments, endothelium-dependent responses were not altered by the presence of 10 or 100 nM nGH or GH. CONCLUSION: In coronary microvessels, and coronary, femoral, mesenteric and renal arteries, GH is not responsible for the impaired endothelial function associated with diabetes mellitus.

Use of the second-generation antipsychotic, risperidone, and secondary weight gain are associated with an altered gut microbiota in children.

The atypical antipsychotic risperidone (RSP) is often associated with weight gain and cardiometabolic side effects. The mechanisms for these adverse events are poorly understood and, undoubtedly, multifactorial in etiology. In light of growing evidence implicating the gut microbiome in the host's energy regulation and in xenobiotic metabolism, we hypothesized that RSP treatment would be associated with changes in the gut microbiome in children and adolescents. Thus, the impact of chronic (>12 months) and short-term use of RSP on the gut microbiome of pediatric psychiatrically ill male participants was examined in a cross-sectional and prospective (up to 10 months) design, respectively. Chronic treatment with RSP was associated with an increase in body mass index (BMI) and a significantly lower ratio of Bacteroidetes:Firmicutes as compared with antipsychotic-naïve psychiatric controls (ratio=0.15 vs 1.24, respectively; P<0.05). Furthermore, a longitudinal observation, beginning shortly after onset of RSP treatment, revealed a gradual decrease in the Bacteroidetes:Firmicutes ratio over the ensuing months of treatment, in association with BMI gain. Lastly, metagenomic analyses were performed based on extrapolation from 16S ribosomal RNA data using the software package, Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt). Those data indicate that gut microbiota dominating the RSP-treated participants are enriched for pathways that have been implicated in weight gain, such as short-chain fatty acid production.

Endothelium-dependent vasodilation of proximal coronary arteries from exercise-trained pigs.

We recently reported that alpha-adrenergic vasoconstriction is blunted and adenosine-induced vasodilation is enhanced in proximal coronary arteries of exercise-trained miniature swine [C. L. Oltman, J. L. Parker, H. R. Adams, and M. H. Laughlin. Am. J. Physiol. 263 (Heart Circ. Physiol. 32): H372-H382, 1992]. The purpose of the present study was to determine whether this model of exercise training also alters endothelium-dependent vasodilator responses of proximal coronary arteries. Female Yucatan miniature swine were exercise trained (ET) on a motor-driven treadmill or were cage confined (Sed) for 13-20 wk. Exercise tolerance, heart weight-to-body weight ratios, and skeletal muscle oxidative capacity were all significantly greater in ET than in Sed animals. Vasodilator responses were evaluated in vitro by determining concentration-response curves by using vascular rings (3.5-4 mm in axial length) isolated from right and left coronary arteries. Vasorelaxation responses were determined, after tone had been produced with either 30 microM prostaglandin F2 alpha, 30 mM KCl, or 30 nM endothelin. Concentration-response curves were obtained to endothelium-dependent vasodilators including bradykinin (10(-9)-10(-6) M), substance P (10(-12)-10(-6) M), clonidine (10(-9)-10(-6) M), serotonin (10(-10)-10(-5) M), and the Ca2+ ionophore A-23187 (10(-10)-10(-6) M). Endothelium-independent vasodilator responses to sodium nitroprusside (10(-9)-10(-4) M) were not different between arteries from Sed and ET. Bradykinin, substance P, and A-23187 were potent vasodilators in arteries from both groups, whereas serotonin and clonidine did not consistently produce vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise training-induced adaptations in the coronary circulation.

Aerobic exercise training induces an increase in coronary blood flow capacity that is associated with altered control of coronary vascular resistance and, therefore, coronary blood flow. The relative importance of metabolic, myogenic, endothelium-mediated, and neurohumoral control systems varies throughout the coronary arterial tree, and these control systems contribute in parallel to regulating coronary vascular resistance to differing degrees at each level in the coronary arterial tree. In addition to this nonuniformity of the relative importance of vascular control systems in the coronary arterial tree, it appears that exercise training-induced adaptations are also distributed spatially, in a nonuniform manner throughout the coronary tree. As a result, it is necessary to examine training-induced adaptations throughout the coronary arterial tree. Adaptations in endothelium-mediated control play a role in training-induced changes in control of coronary vascular resistance, and there is evidence that the effects of training may be different in large coronary arteries than in the microcirculation. Also, there is evidence that the mode, frequency, and intensity of exercise training bouts and duration of training may influence the adaptive changes in endothelial function. Exercise training has also been shown to induce changes in responses of coronary vascular smooth muscle to vasoactive agents and alterations in the cellular-molecular control of intracellular Ca2+ in coronary vascular smooth muscle of conduit coronary arteries and to enhance myogenic reactivity of coronary resistance arteries. Exercise training also appears to have different effects on vascular smooth muscle in large coronary arteries than in the microcirculation. For example, adenosine sensitivity is increased in conduit coronary arteries and large resistance arteries after training but is not altered in small coronary resistance arteries of trained animals. Although much remains to be studied, evidence clearly indicates that chronic exercise alters the phenotype of coronary endothelial and vascular smooth muscle cells and that plasticity of these cells plays a role in adaptation of the cardiovascular system in exercise training.

Effects of exercise training on regulation of tone in coronary arteries and arterioles.

A large number of studies now support the concept that exercise training alters functional control of the coronary circulation. Recent work has approached this area using ex vivo coronary arterial preparations (proximal coronary arteries, near-resistance arteries, resistance arterioles) isolated from exercise-trained animals and contracting independently of confounding in vivo influences. The combined results of these studies indicate that training-induced alterations in vascular control mechanisms do not occur uniformly throughout the coronary vascular tree. Proximal epicardial coronary arteries (approximately 2.0 mm diameter) isolated from exercise-trained pigs exhibited significantly reduced contractile responsiveness to the alpha-adrenergic receptor agonist, norepinephrine, but unaltered contractile responsiveness to K+, acetylcholine, and endothelin. Also, proximal arteries from exercise-trained animals demonstrated enhanced sensitivity to the vasodilator effects of adenosine. At the other end of the vascular spectrum, in resistance arterioles (< 150 microns diameter) the relaxation responses to adenosine were unaffected by exercise training, but bradykinin-induced vasodilation (endothelium-dependent) was significantly enhanced. In near-resistance arteries (150-240 microns diameter) responses to both bradykinin and adenosine were enhanced by exercise training. Thus, exercise training is associated with intrinsic vessel size-dependent alterations in coronary smooth muscle and endothelium-mediated regulatory mechanisms.

Effects of exercise training on vasomotor reactivity of porcine coronary arteries.

The purpose of this study was to determine whether exercise training induces changes in the contractile behavior of proximal coronary arteries. Female Yucatan miniature swine were either exercise trained (ET) on a motor-driven treadmill or allowed to remain sedentary (SED) for 16-22 wk. Responses to vasoactive compounds were evaluated in vitro using coronary arterial rings (approximately 2 mm diam) isolated from ET and SED pigs. Each ring was stretched to the apex of the length-active tension relationship. Concentration-response relationships for isometric contractions evoked with KCl (5-100 mM), prostaglandin F2 alpha (PGF2 alpha; 10(-8)-3 x 10(-5) M), acetylcholine (ACh; 10(-9)-10(-4) M), and endothelin (10(-10)-10(-7) M) were similar in arteries from SED and ET pigs. In contrast, arteries from the ET group developed 50-60% less maximal tension in response to norepinephrine (NE; 10(-6)-10(-4) M) than did controls. Vasodilator responses of rings precontracted with either KCl or PGF2 alpha were evaluated with adenosine (ADO; 10(-9)-10(-4) M), isoproterenol (10(-9)-10(-4) M), forskolin (10(-9)-10(-4) M), and sodium nitroprusside (NP; 10(-10)-10(-4) M). Vasodilator responses were similar in SED and ET groups for all agents except ADO and NP; arteries from ET pigs were more sensitive to ADO and less sensitive to NP. The ET-induced alterations in vasomotor responses to NE and ADO appear to be due to changes in vascular smooth muscle because they were still present after removal of endothelium. We conclude that chronic exercise training in pigs induces selective alterations in NE and ADO receptor-second messenger coupling and/or postreceptor-related events in epicardial coronary vascular smooth muscle.

Epoxyeicosatrienoic acids and dihydroxyeicosatrienoic acids are potent vasodilators in the canine coronary microcirculation.

Cytochrome P450 epoxygenases convert arachidonic acid into 4 epoxyeicosatrienoic acid (EET) regioisomers, which were recently identified as endothelium-derived hyperpolarizing factors in coronary blood vessels. Both EETs and their dihydroxyeicosatrienoic acid (DHET) metabolites have been shown to relax conduit coronary arteries at micromolar concentrations, whereas the plasma concentrations of EETs are in the nanomolar range. However, the effects of EETs and DHETs on coronary resistance arterioles have not been examined. We administered EETs and DHETs to isolated canine coronary arterioles (diameter, 90.0+/-3.4 microm; distending pressure, 20 mm Hg) preconstricted by 30% to 60% of the resting diameter with endothelin. All 4 EET regioisomers produced potent, concentration-dependent vasodilation (EC50 values ranging from -12.7 to -10.1 log [M]) and were approximately 1000 times more potent than reported in conduit coronary arteries. The vasodilation produced by 14,15-EET was not attenuated by removal of the endothelium and indicated a direct action of 14,15-EET on microvascular smooth muscle. Likewise, 14,15-DHET, 11,12-DHET, 8,9-DHET, and the delta-lactone of 5,6-EET produced extremely potent vasodilation (EC50 values ranging from -15.8 to -13.1 log [M]). The vasodilation produced by these eicosanoids was highly potent in comparison to that produced by other vasodilators, including arachidonic acid (EC50=-7.5 log [M]). The epoxide hydrolase inhibitor, 4-phenylchalone oxide, which blocked the conversion of [3H]14,15-EET to [3H]14,15-DHET by canine coronary arteries, did not alter arteriolar dilation to 11,12-EET; thus, the potent vasodilation induced by EETs does not require formation of DHETs. In contrast, charybdotoxin (a KCa channel inhibitor) and KCl (a depolarizing agent) blocked vasodilation by 11,12-EET and 11,12-DHET. We conclude that EETs and DHETs potently dilate canine coronary arterioles via activation of KCa channels. The preferential ability of these compounds to dilate resistance blood vessels suggests that they may be important regulators of coronary circulation.

Calcium-activated potassium channels mask vascular dysfunction associated with oxidized LDL exposure in rabbit aorta.

Endothelium-dependent vasodilation is impaired in atherosclerosis. Oxidized low density lipoprotein (ox-LDL) plays an important role, possibly through alterations in G-protein activation. We examined the effect of acute exposure to ox-LDL on the dilator responses of isolated rabbit aorta segments. We sought also to evaluate the specificity of this dysfunction for dilator stimuli that traditionally operate through a Gi-protein mechanism. Aortic segments were prepared for measurement of isometric tension. After contraction with prostaglandin F2alpha, relaxation to thrombin, adenosine diphosphate (ADP), or the endothelium-independent agonists, sodium nitroprusside (SNP) or papaverine was examined. Maximal relaxation to thrombin was impaired in the presence of ox-LDL (17.7+/-3.7% p<0.05) compared to control (no LDL) (52.6+/-4.0%). Ox-LDL did not affect maximal relaxation to ADP or SNP. However, in the presence of charybdotoxin (CHTX: calcium-activated potassium channel inhibitor) ox-LDL impaired relaxation to ADP (17.4+/-3.2%). CHTX did not affect control (no LDL) responses to ADP (69.6+/-5.0%) or relaxation to thrombin or papaverine. In conclusion, ox-LDL impairs relaxation to thrombin, but in the case of ADP, calcium-activated potassium channels compensate to maintain this relaxation.

EET homologs potently dilate coronary microvessels and activate BK(Ca) channels.

Epoxyeicosatrienoic acids (EETs) are released from endothelial cells and potently dilate small arteries by hyperpolarizing vascular myocytes. In the present study, we investigated the structural specificity of EETs in dilating canine and porcine coronary microvessels (50-140 microm ID) and activating large-conductance Ca2+-activated K+ (BK(Ca)) channels. The potencies and efficacies of EET regioisomers and enantiomers were compared with those of two EET homologs: epoxyeicosaquatraenoic acids (EEQs), which are made from eicosapentaenoic acid by the same cytochrome P-450 epoxygenase that generates EETs from arachidonic acid, and epoxydocosatetraenoic acids (EDTs), which are EETs that are two carbons longer. With EC50 values of 3-120 pM but without regio- or stereoselectivity, EETs potently dilated canine and porcine microvessels. Surprisingly, the EEQs and EDTs had comparable potencies and efficacies in dilating microvessels. Moreover, 50 nM 13,14-EDT activated the BK(Ca) channels with the same efficacy as either 11,12-EET enantiomer at 50 nM. We conclude that coronary microvessels and BK(Ca) channels possess low structural specificity for EETs and suggest that EEQs and EDTs may thereby also be endothelium-derived hyperpolarizing factors.

Mechanism of coronary vasodilation to insulin and insulin-like growth factor I is dependent on vessel size.

Insulin and insulin-like growth factor I (IGF-I) influence numerous metabolic and mitogenic processes; these hormones also have vasoactive properties. This study examined mechanisms involved in insulin- and IGF-I-induced dilation in canine conduit and microvascular coronary segments. Tension of coronary artery segments was measured after constriction with PGF(2alpha). Internal diameter of coronary microvessels (resting diameter = 112.6+/-10.1 microm) was measured after endothelin constriction. Vessels were incubated in control (Krebs) solution and were treated with N(omega)-nitro-L-arginine (L-NA), indomethacin, or K(+) channel inhibitors. After constriction, cumulative doses of insulin or IGF-I (0.1-100 ng/ml) were administered. In conduit arteries, insulin produced modest maximal relaxation (32 +/- 5%) compared with IGF-I (66+/-12%). Vasodilation was attenuated by nitric oxide synthase (NOS) and cyclooxygenase inhibition and was blocked with KCl constriction. Coronary microvascular relaxation to insulin and IGF-I was not altered by L-NA, indomethacin, tetraethylammonium chloride, glibenclamide, charybdotoxin, and apamin; however, tetrabutylammonium chloride attenuated the response. In conclusion, insulin and IGF-I cause vasodilation in canine coronary conduit arteries and microvessels. In conduit vessels, NOS/cyclooxygenase pathways are involved in the vasodilation. In microvessels, relaxation to insulin and IGF-I is not mediated by NOS/cyclooxygenase pathways but rather through K(+)-dependent mechanisms.

Endothelium-derived hyperpolarizing factor in coronary microcirculation: responses to arachidonic acid.

In coronary resistance vessels, endothelium-derived hyperpolarizing factor (EDHF) plays an important role in endothelium-dependent vasodilation. EDHF has been proposed to be formed through cytochrome P-450 monooxygenase metabolism of arachidonic acid (AA). Our hypothesis was that AA-induced coronary microvascular dilation is mediated in part through a cytochrome P-450 pathway. The canine coronary microcirculation was studied in vivo (beating heart preparation) and in vitro (isolated microvessels). Nitric oxide synthase (NOS) (N(omega)-nitro-L-arginine, 100 microM) and cyclooxygenase (indomethacin, 10 microM) or cytochrome P-450 (clotrimazole, 2 microM) inhibition did not alter AA-induced dilation. However, when a Ca(2+)-activated K(+) channel channel or cytochrome P-450 antagonist was used in combination with NOS and cyclooxygenase inhibitors, AA-induced dilation was attenuated. We also show a negative feedback by NO on NOS-cyclooxygenase-resistant AA-induced dilation. We conclude that AA-induced dilation is attenuated by cytochrome P-450 inhibitors, but only when combined with inhibitors of cyclooxygenase and NOS. Therefore, redundant pathways appear to mediate the AA response in the canine coronary microcirculation.

12-lipoxygenase in porcine coronary microcirculation: implications for coronary vasoregulation.

Noncyclooxygenase metabolites of arachidonic acid (AA) have been proposed to mediate endothelium-dependent vasodilation in the coronary microcirculation. Therefore, we examined the formation and bioactivity of AA metabolites in porcine coronary (PC) microvascular endothelial cells and microvessels, respectively. The major noncyclooxygenase metabolite produced by microvascular endothelial cells was 12(S)-hydroxyeicosatetraenoic acid (HETE), a lipoxygenase product. 12(S)-HETE release was markedly increased by pretreatment with 13(S)-hydroperoxyoctadecadienoic acid but not by the reduced congener 13(S)-hydroxyoctadecadienoic acid, suggesting oxidative upregulation of 12(S)-HETE output. 12(S)-HETE produced potent relaxation and hyperpolarization of PC microvessels (EC(50), expressed as -log[M] = 13.5 +/- 0.5). Moreover, 12(S)-HETE potently activated large-conductance Ca(2+)-activated K(+) currents in PC microvascular smooth muscle cells. In contrast, 12(S)-HETE was not a major product of conduit PC endothelial AA metabolism and did not exhibit potent bioactivity in conduit PC arteries. We suggest that, in the coronary microcirculation, 12(S)-HETE can function as a potent hyperpolarizing vasodilator that may contribute to endothelium-dependent relaxation, particularly in the setting of oxidative stress.