The Effect of Endotoxin on General and Coronary Haemodynamics and Metabolism, and its Relation in Certain Infectious Diseases

Shock occurs in gram-negative septicaemia, dengue, and other infections: to understand the situation better, a study was made of the effects of endotoxin on the general and coronary circulation of intact animals. Cardiac output (Fick), coronary flow (N2O Fick), vascular pressures, glucose lactate, pyruvate, non-esterified fatty acid (NEFA), and C14 palmitate levels, were measured before and after the injection of Serratia marcescens endotoxin into healthy anaesthetized dogs.Cardiac output, vascular pressures, and cardiac work fell precipitously. Coronary blood flow, myocardial O2 consumption, and cardiac efficiency decreased by 50%.Whole-body glucose, lactate, pyruvate, and NEFA increased, but no change occurred in the myocardial extraction of these substances. The myocardial oxidation of C14 palmitate increased.The general haemodynamic changes are similar to those occurring in patients; it is suggested that the changes in the coronary circulation seen in animals may also occur in the clinical situation. Other animal studies with a histamine releaser (Tween 20), gave results similar to those of endotoxin. Anaphylotoxins may then also be relevant to the "shock" state of certain infections.

Nitric oxide regulation of myocardial O2 consumption and HEP metabolism

NO and O2 compete at cytochrome- c oxidase, thus potentially allowing NO to modulate mitochondrial respiration. We previously observed a decrease of myocardial phosphocreatine (PCr)/ATP during very high cardiac work states, corresponding to an increase in cytosolic free ADP. This study tested the hypothesis that NO inhibition of respiration contributes to this increase of ADP. Infusion of dobutamine + dopamine (DbDp, each 20 μg·kg−1·min−1 iv) to more than double myocardial oxygen consumption (MV̇o2) in open-chest dogs caused a decrease of myocardial PCr/ATP measured with 31P NMR from 2.04 ± 0.09 to 1.85 ± 0.08 ( P < 0.05). Inhibition of NO synthesis with Nω-nitro-l-arginine (l-NNA), while catecholamine infusion continued, caused PCr/ATP to increase to the control value. In a second group of animals, l-NNA administered before catecholamine stimulation (reverse intervention of the first group) increased PCr/ATP during basal conditions. In these animals l-NNA did not prevent a decrease of PCr/ATP at the high cardiac work state but, relative to MV̇o2, PCr/ATP was significantly higher after l-NNA. In a third group of animals, pharmacological coronary vasodilation with carbochromen was used to prevent changes in coronary flow that might alter endothelial NO production. In these animals l-NNA again restored depressed myocardial PCr/ATP during catecholamine infusion. The finding that inhibition of NO production increased PCr/ATP suggests that during very high work states NO inhibition of mitochondrial respiration requires ADP to increase to drive oxidative phosphorylation.

Endothelial NO formation does not control myocardial O2 consumption in mouse heart

To test whether endothelium-derived nitric oxide (NO) regulates mitochondrial respiration, NO was pharmacologically modulated in isolated mouse hearts, which were perfused at constant flow to sensitively detect small changes in myocardial O2 consumption (MV̇O2). Stimulation of NO formation by 10 μM bradykinin (BK) increased coronary venous nitrite release fivefold to 58 ± 33 nM ( n = 17). Vasodilatation by BK, adenosine (1 μM), or papaverine (10 μM) decreased perfusion pressure, left ventricular developed pressure (LVDP), and MV̇O2. In the presence of adenosine-induced vasodilatation, stimulation of endothelial NO synthesis by BK had no effect on LVDP and MV̇O2. Also, inhibition of NO formation by NG-monomethyl-l-arginine (l-NMMA, 100 μM) did not significantly alter LVDP and MV̇O2. Similarly, intracoronary infusion of authentic NO ≤2 μM did not influence LVDP or MV̇O2 (-1 ± 1%). Only when NO was >2 μM were contractile dysfunction and MV̇O2 reduction observed. Because BK-induced stimulation of endothelial NO formation and basal NO are not sufficient to impair MV̇O2 in the saline-perfused mouse heart, a tonic control of the respiratory chain by endothelial NO is difficult to conceive.

Compensatory changes in Ca2+ and myocardial O2 consumption in β-tropomyosin transgenic hearts

Transgenic mice overexpressing β-tropomyosin have increased myofilament Ca2+ sensitivity that we hypothesized would result in altered relationships among pressure and heart rates, intracellular Ca2+, and myocardial O2 consumption. In perfused hearts from transgenic mice there was a marked negative force-frequency response between 6 and 10 Hz with a 30 ± 3% reduction in peak-positive first derivative of pressure development over time (dP/d t) compared with 14 ± 2% in wild-type mice ( P < 0.001). At 8 Hz systolic pressures were normal, though peak systolic intracellular Ca2+ was significantly reduced in transgenic mice versus wild type (726 ± 61 vs. 936 ± 67 nM, P < 0.05) indicating an alteration in the pressure-Ca2+ relationship. Over a wide range of positive and negative inotropic interventions there were normal developed pressures, though marked elevations in myocardial O2 consumption (15–54%). Because pressures are normal and intracellular Ca2+ decreased and myocardial O2 consumption increased, this suggests that these abnormalities are at least in part compensatory mechanisms to the altered myofilament function.

Impaired dilation of coronary arterioles during increases in myocardial O2 consumption with hyperglycemia

Previous studies showed that nitric oxide (NO) plays an important role in coronary arteriolar dilation to increases in myocardial oxygen consumption (MV˙o 2). We sought to evaluate coronary microvascular responses to endothelium-dependent and to endothelium-independent vasodilators in an in vivo model. Microvascular diameters were measured using intravital microscopy in 10 normal (N) and 9 hyperglycemic (HG; 1 wk alloxan, 60 mg/kg iv) dogs during suffusion of acetylcholine (1, 10, and 100 μM) or nitroprusside (1, 10, and 100 μM) to test the effects on endothelium-dependent and -independent dilation. During administration of acetylcholine, coronary arteriolar dilation was impaired in HG, but was normal during administration of nitroprusside. To examine a physiologically important vasomotor response, 10 N and 7 HG control, 5 HG and 5 N during superoxide dismutase (SOD), and 5 HG and 4 N after SQ29,548 (SQ; thromboxane A2/prostaglandin H2receptor antagonist) dogs were studied at three levels of MV˙o 2: at rest, during dobutamine (DOB; 10 μg · kg−1 · min−1 iv), and during DOB with rapid atrial pacing (RAP; 280 ± 10 beats/min). During dobutamine, coronary arterioles dilated similarly in all groups, and the increase in MV˙o 2 was similar among the groups. However, during the greater metabolic stimulus (DOB+RAP), coronary arterioles in N dilated (36 ± 4% change from diameter at rest) significantly more than HG (16 ± 3%, P< 0.05). In HG+SQ and in HG+SOD, coronary arterioles dilated similarly to N, and greater than HG ( P < 0.05). MV˙o 2 during DOB+RAP was similar among groups. Normal dogs treated with SOD and SQ29,548 were not different from untreated N dogs. Thus, in HG dogs, dilation of coronary arterioles is selectively impaired in response to administration of the endothelium-dependent vasodilator acetylcholine and during increases in MV˙o 2.

A 13C NMR double-labeling method to quantitate local myocardial O2 consumption using frozen tissue samples

Measurement of local myocardial O2 consumption (V˙o 2) has been problematic but is needed to investigate the heterogeneity of aerobic metabolism. The goal of the present investigation was to develop a method to measure local V˙o 2 using small frozen myocardial samples, suitable for determiningV˙o 2 profiles. In 26 isolated rabbit hearts, 1.5 mmol/l [2-13C]acetate was infused for 4 min, followed by 1.5 min of [1,2-13C]acetate. The left ventricular (LV) free wall was then quickly frozen. High-resolution 13C-NMR spectra were measured from extracts taken from 2- to 3-mm thick transmural layer samples. The multiplet intensities of glutamate were analyzed with a computer model allowing simultaneous estimation of the absolute flux through the tricarboxylic acid cycle and the fractional contribution of acetate to acetyl CoA formation from which localV˙o 2 was calculated. The 13C-derivedV˙o 2 in the LV free wall was linearly related to “gold standard”V˙o 2 from coronary venous O2 electrode measurements in the same region ( r = 0.932, n = 22, P < 0.0001, slope 1.05) for control and lowered metabolic rates. The ratio of subendocardial to subepicardial V˙o 2 was 1.52 ± 0.19 (SE, significantly >1, P< 0.025). Local myocardialV˙o 2 can now be quantitated with this new 13C method to determine profiles of aerobic energy metabolism.