Recombinant glucagon-like peptide-1 increases myocardial glucose uptake and improves left ventricular performance in conscious dogs with pacing-induced dilated cardiomyopathy.

BACKGROUND: The failing heart demonstrates a preference for glucose as its metabolic substrate. Whether enhancing myocardial glucose uptake favorably influences left ventricular (LV) contractile performance in heart failure remains uncertain. Glucagon-like peptide-1 (GLP-1) is a naturally occurring incretin with potent insulinotropic effects the action of which is attenuated when glucose levels fall below 4 mmol. We examined the impact of recombinant GLP-1 (rGLP-1) on LV and systemic hemodynamics and myocardial substrate uptake in conscious dogs with advanced dilated cardiomyopathy (DCM) as a mechanism for overcoming myocardial insulin resistance and enhancing myocardial glucose uptake. METHODS AND RESULTS: Thirty-five dogs were instrumented and studied in the fully conscious state. Advanced DCM was induced by 28 days of rapid pacing. Sixteen dogs with advanced DCM received a 48-hour infusion of rGLP-1 (1.5 pmol x kg(-1) x min(-1)). Eight dogs with DCM served as controls and received 48 hours of a saline infusion (3 mL/d). Infusion of rGLP-1 was associated with significant (P<0.02) increases in LV dP/dt (98%), stroke volume (102%), and cardiac output (57%) and significant decreases in LV end-diastolic pressure, heart rate, and systemic vascular resistance. rGLP-1 increased myocardial insulin sensitivity and myocardial glucose uptake. There were no significant changes in the saline control group. CONCLUSIONS: rGLP-1 dramatically improved LV and systemic hemodynamics in conscious dogs with advanced DCM induced by rapid pacing. rGLP-1 has insulinomimetic and glucagonostatic properties, with resultant increases in myocardial glucose uptake. rGLP-1 may be a useful metabolic adjuvant in decompensated heart failure.

The development of myocardial insulin resistance in conscious dogs with advanced dilated cardiomyopathy.

BACKGROUND: The failing heart demonstrates a preference for glucose as its metabolic substrate. Advanced, severe DCM is characterized by depletion of adenosine triphosphate (ATP) stores, which may be a consequence of impaired insulin mediated glucose uptake and oxidation at a time when the myocardium prefers glucose as its substrate. We examined the time course and magnitude of myocardial insulin resistance during the evolution of dilated cardiomyopathy. METHODS AND RESULTS: Thirty-four conscious, chronically instrumented dogs were studied at four stages during the evolution of dilated cardiomyopathy (DCM) induced by rapid RV pacing [control, early, late and advanced severe]. Transmyocardial glucose, lactate, and non-esterified fatty acid (NEFA) concentrations were measured in the fasting state. The cellular insulin signaling cascade and ATP levels were measured on myocardial samples. NEFA and insulin concentrations increased early and progressively in DCM in association with increased norepinephrine concentrations and progressive hemodynamic impairment. In advanced DCM but not earlier stages, myocardial ATP levels were decreased by 34%. There was decreased myocardial glucose uptake evident under both basal (-29 +/- 5%) and insulin stimulated (-32 +/- 4%) conditions in advanced, severe DCM, associated with a 31% reduction in GLUT-4 translocation. Importantly, there were no alterations in proximal steps in insulin signaling, but significant reductions in serine (Ser473) phosphorylation of Akt-1. CONCLUSIONS: Advanced, severe DCM is associated with the development of myocardial insulin resistance. There is impaired myocardial glucose uptake and altered myocardial insulin signaling, involving decreased Ser 473 phosphorylation of Akt-1. Myocardial insulin resistance in advanced, severe DCM was also associated with reduced myocardial ATP levels.

Catecholamine stimulation is associated with impaired myocardial O(2) utilization in heart failure.

OBJECTIVES: To investigate the effect of alpha,beta(1) and beta(2) adrenergic receptor (AR) stimulation on coronary hemodynamics, myocardial oxygen consumption (M(v)O(2)) and metabolic substrate preference in advanced dilated cardiomyopathy (DCM). METHODS: We studied 19 conscious, instrumented dogs with pacing-induced DCM. We evaluated systemic, coronary hemodynamics and M(v)O(2) in response to norepinephrine (NOR, 0.05-0.4 microg/kg per min), dobutamine (DOB, 1-10 microg/kg per min), phenylephrine (PHE, 1-5 microg/kg per min) and isoproterenol (ISO, 0.05-0.4 microg/kg per min) alone or in the presence of metoprolol (ISO+MET). Experiments were conducted in control state and in advanced DCM, 4-5 weeks after the initiation of pacing. RESULTS: Contractile responses (LV dP/dt) to catecholamines were desensitized and accompanied by a parallel decrease in heart rate-adjusted myocardial O(2) consumption (M(v)O(2/beat)), when alpha(PHE) or beta(1) (DOB) or both alpha/beta(1) (NOR) AR were stimulated in DCM. This was due to impaired transmyocardial (Ao-Cs) O(2) extraction rather than limitations in CBF responses. There was an associated shift in myocardial metabolism, evidenced by an increased preference for glycolytic substrates (Respiratory Quotient) following administration of any of these three adrenergic agonists in DCM. Combined beta(1)/beta(2) stimulation with ISO or beta(2)-AR stimulation (ISO+MET) in DCM resulted in greater M(v)O(2/beat), [(Ao-Cs) O(2)] extraction, and decreases in myocardial RQ consistent with a shift toward oxidation of FFA. CONCLUSIONS: The impairment in contractile responses to dobutamine and norepinephrine in DCM is associated with impaired myocardial O(2) extraction, and a shift toward a preference for glycolysis. A different myocardial metabolic pattern suggestive of increased oxidation of FFA with increased myocardial O(2) extraction was observed in the presence of combined beta(1)/beta(2) stimulation with isoproterenol or beta(2) stimulation (ISO+MET). These data suggest that beta(2)-AR stimulation in DCM shifts substrate preference toward FFA oxidation associated with greater M(v)O(2) requirements. These findings identify a putative metabolic effect of beta(2) -AR in DCM that may be deleterious.

Quantitative reverse transcription-polymerase chain reaction of GABA(A) alpha1, beta1 and gamma2S subunits in epileptic rats following photothrombotic infarction of neocortex.

Photothrombotic brain infarction can result in altered expression of cortical GABA(A) receptors and in epileptic seizures. We sought to determine whether infarct size and/or epileptic seizures resulted in a differential expression of cortical GABA(A) receptor subunit mRNA in adult rats. A reverse transcription-polymerase chain reaction (RT-PCR) was used with internal standards for GABA(A) receptor subunits to quantify alpha(1), beta(1), and gamma(2S) subunit mRNA expression in cortex ipsilateral and contralateral to left cerebral infarcts in small or large infarct/nonepileptic cohorts, a large infarct/epileptic cohort, and a young adult control cohort. Unilateral hemispheric subunit mRNA was pooled for each cohort, quantified, and expressed as mean values+/-S.E.M. In general, the magnitude of mRNA expression (pg/1 microg total RNA) was different for the individual subunits: gamma(2S) (10(4)), alpha(1) (10(2)), and beta(1) (10(1)). Hemispheric subunit mRNA expression for the different cohorts was compared by ANOVA testing, which noted significant differences for the alpha(1) (P<0.001) and beta(1) (P<0.001) subunits in ipsilateral cortex. Bonferroni post-testing for alpha(1) cohorts indicated that mRNA expression for the large infarct/epilepsy cohort (624.2+/-6.8 pg) was greater than all other cohorts (P<0.001); control (162.7+/-32.2 pg). For beta(1) cohorts, there was decreased mRNA expression in the large infarct/nonepileptic cohort (9.2+/-0.8 pg; P<0.01) and the large infarct/epileptic cohort (10.5+/-2.2 pg; P<0.05) compared to control (23.2+/-2.6 pg). Additionally, paired t-tests compared subunit mRNA expression within individual animal cohorts (ipsilateral vs. contralateral) and indicated decreased mRNA expression ipsilaterally for the beta(1) subunit in the small infarct cohort (14.2+/-2.6 vs. 22.9+/-3.0 pg; P=0.0102) and the large infarct/epilepsy cohort (10.5+/-2.3 vs. 18.0+/-3.6 pg; P=0.0462). These findings suggest that large photothrombotic infarcts of the neocortex can result in a long-lasting differential expression of GABA(A) receptor subunit mRNAs in ipsilateral cortex variably associated with the epileptic state.

Chronic exposure to cocaine binging predisposes to an accelerated course of dilated cardiomyopathy in conscious dogs following rapid ventricular pacing.

Despite extensive study, the extent to which cocaine use predisposes to cardiac injury remains unknown. We hypothesized that chronic cocaine binging would increase susceptibility to a subsequent cardiac insult, even in the absence of demonstrable effects on baseline hemodynamics. We studied progression of dilated cardiomyopathy (DCM) induced by rapid ventricular pacing (240 beats per minute) in five conscious, chronically instrumented dogs, after exposure to repetitive cocaine binging (COC) in the form of four consecutive 1 mg/kg i.v. boluses daily for 8 days, to simulate human cocaine abuse. We compared the results with nine control dogs (CON) undergoing the exact pacing protocol, without prior cocaine exposure. Baseline hemodynamics were not significantly altered by chronic cocaine exposure. Following 2 weeks of pacing, COC dogs exhibited accelerated progression to DCM, depressed plasma nitric oxide levels (CON, 17 +/- 2 microM; COC, 10 +/- 2 microM, p < 0.05), and a significantly greater increase in plasma epinephrine (CON, 33 +/- 6 pg/ml; COC, 104 +/- 24 pg/ml). After only 2 weeks of pacing, COC dogs demonstrated progressive DCM of a magnitude comparable with end-stage pacing-induced DCM. Chronic cocaine binging increases susceptibility to a subsequent myocardial insult and accelerates progression of DCM in conscious dogs following rapid pacing. These data suggest that although chronic cocaine use alone may not affect myocardial function, it predisposes to greater susceptibility to a superimposed insult.

Coronary blood flow responses are impaired independent of NO and endothelial function in conscious dogs with dilated cardiomyopathy.

BACKGROUND: Dilated cardiomyopathy (DCM) is characterized by nitric oxide (NO) deficiency and endothelial dysfunction. Whether endothelium-independent vasodilation is preserved, particularly in the coronary circulation, remains controversial. METHODS AND RESULTS: We studied systemic and coronary flow responses to the endothelium-dependent agonist, acetylcholine, the cGMP-dependent NO-donor, nitroglycerin, the predominantly endothelium-independent agonist, adenosine, the beta-adrenergic cAMP-dependent agonist, isoproterenol, and the calcium channel antagonist, nicardipine, in conscious dogs with pacing-induced DCM. Systemic blood flow response was impaired to acetylcholine but preserved to other vasodilators in DCM. In contrast, coronary blood flow response was significantly ( P < .05) depressed to all agonists. (Peak coronary blood flow response, control versus DCM: acetylcholine: 221 +/- 14% versus 156 +/- 11%; nitroglycerin: 220 +/- 17% versus 138 +/- 9%; adenosine: 635 +/- 65% versus 376 +/- 56%; nicardipine: 338 +/- 59% versus 115 +/- 23%; isoproterenol: 219 +/- 18% versus 86 +/- 20%). The attenuation was independent of systemic hemodynamic differences. CONCLUSION: In contrast to systemic responses, coronary blood flow responses in DCM are impaired dependent or independent of NO or second messenger mechanisms, implying either distal signaling defects or structural abnormalities in the coronary vasculature.