Die Wirkung von Isoproterenol, Adrenalin, Noradrenalin und Adenosin auf die Durchblutung und den O2-Verbrauch des Herzmuskels vor und nach der Blockierung der ?-Receptoren

Isoproternenol increases vascular volume expansion and urinary output after a large crystalloid bolus in healthy volunteers

BACKGROUND

The primary goal of fluid therapy is to maintain fluid homeostasis. Commonly used isotonic crystalloids are only marginally effective and contribute to fluid excess syndrome. In patients with decreased cardiovascular reserve, fluid therapy alone is not sufficient to maintain end-organ perfusion. Therefore, inotropes or vasoactive drugs are used to supplement fluid infusion. Recent animal data suggest that coinfusion of adrenergic agents modulate the distribution of fluid between the vascular and extravascular/interstitial compartments after a fluid bolus. We sought to determine if this effect would translate in humans by coadministering a β-adrenergic agonist with fluid.

METHODS

Nine healthy volunteers (aged 21-50 years) were randomly paired and received either a continuous isoproterenol infusion (ISO: 0.05 μg/kg per minute) or 0.9% saline (control [CON]) 30min prior to a 25 mL/kg 0.9% NaCl fluid bolus. Hemodynamics, ventricular volume and function, and microcirculatory determinants (capillary filtration coefficient and oncotic pressure) were measured. Vascular and extravascular volume and fluid balance were determined.

RESULTS

Compared with CON, ISO significantly increased heart rate (CON: 64.2 ± 4.1 beats/min vs. ISO: 97.4 ± 5.7 beats/min) and cardiac output (CON: 4.4 ± 0.7 L/min vs. ISO: 10.2 ± 0.9) before fluid bolus. Isoproterenol significantly increased urinary output (ISO: 10.86 ± 1.95 vs. control: 6.53 ± 1.45 mL/kg) and reduced extravascular volume (7.98 ± 2.0 vs. 14.15 ± 1.1mL/kg). Isoproterenol prevented an increase in capillary filtration coefficient (1.74 ± 0.4 vs. 3.21 ± 0.4 mL/min per mmHg · 10).

CONCLUSIONS

Isoproterenol, a nonselective β-adrenergic agonist, augments vascular volume expansion and eliminates extravascular volume via enhanced diuresis, which may in part be due to enhanced endothelial barrier function.

Epinephrine in resuscitation: curse or cure?

The use of epinephrine during cardiac arrest has been advocated for decades and forms an integral part of the published guidelines. Its efficacy is supported by animal data, but human trial evidence is lacking. This is partly attributable to disparities in trial methodology. Epinephrine’s pharmacologic and physiologic effects include an increase in coronary perfusion pressure that is key to successful resuscitation. One possible explanation for the lack of epinephrine’s demonstrated efficacy in human trials of out-of-hospital cardiac arrest is the delay in its administration. A potential solution may be intraosseus epinephrine, which can be administered quicker. More importantly, it is the quality of the basic life support, early and uninterrupted chest compressions, early defibrillation and postresuscitation care that will provide the best chance of neurologically intact survival.

Adenosine-induced increase in myocardial adenine nucleotides without adenosine-induced systemic hypotension

In anaesthetized rabbits, the i.v. application of 1% adenosine (Ado) for 3 hours at a rate of 4 ml X h-1 X kg-1 body weight increased the myocardial tissue levels of adenine nucleotides (AN) above the normal values by 39%. This increase in ATP and the sum of AN is a metabolic effect of the continuous and high supply of Ado and does not result from the Ado-induced systemic hypotension: Neither a comparable hypotension and reduction of circulatory work induced by phentolamine nor a massive volume loading caused changes in the AN. The compensation of the Ado-induced hypotension by a simultaneous i.v. application of caffeine or xylometazoline did not interfere with the accumulation of AN. The increase in AN was less pronounced, if norepinephrine was infused to maintain normotension. The increase in AN occurred in left and right ventricular myocardium to a similar extent, although the pressure-volume-work of the left ventricle decreased, and that of the right ventricle increased during Ado-application.

Effects of a 2-substituted adenosine derivative, 2-(p-methoxyphenyl)-adenosine (CV-1674) on coronary and cardiohemodynamics, and myocardial energetics

In dogs, intracoronary doses of CV-1674, adenosine ( ADS) and 2-Cl-ADS for doubling coronary flow were estimated as 5.0, 2.0 and 0.4 microgram/dog, and i.v. doses 31, 71 and 2.5 microgram/kg, respectively. ADS and 2-Cl-ADS decreased, while CV-1674 increased LV dp/dt. Intravenous infusion (30 min) of CV-1674 (10 microgram/kg per min) and ADS (700 microgram/kg per min) decreased coronary resistance to approximately the same extent. Decreases in blood pressure, total peripheral resistance and myocardial O2 concumption with ADS were more prominent than those with CV-1674. ADS produced a marked bradycardia that was not evident with CV-1674. Neither agent had a significant influence on myocardial efficiency. In guinea pig atria, ADS and 2-Cl-ADS exerted negative effects while those with CV-1674 were positive inotropic and chronotropic. In cats, intraduodenal ADS (10 mg/kg) produced no effects on cardiohemodynamic parameters. CV-1674 (250 and 500 microgram/kg) increased myocardial tissue blood flow (MBF) with a slight hypotension in a dose-dependent manner, whereas 2-Cl-ADS (100, 250 and 500 microgram/kg) increased MBF only with the highest dose concomitantly with marked hypotension and bradycardia. These results suggest that CV-1674 induces selective coronary vasodilation with less depression on cardiohemodynamics, and is relatively well absorbed from the intestinal tract. The pharmacological profile of the compound, therefore, differs from that of ADS and 2-Cl-ADS.

Vascular and cardiac contractile reserve in the dog heart with chronic multiple coronary occlusions

Nineteen mongrel dogs survived chronic occlusion of the left circumflex and of the right coronary artery without infarction due to the timely development of a collateral circulation. Only 38 per cent of the conductance of the arteries before occlusion was restored by collateral vessels. In these animals and in 15 control dogs with normal coronary arteries myocardial contractility, contractility reserve, and myocardial blood flow were studied. The same was done in dogs with chronic coronary artery occlusion after aortocoronary bypass. Myocardial blood flow was determined woth the tracer microsphere technique. Contractility reserve was tested and defined as isovolumetric left ventricular pressure and dp/dt max with norepinephrine infusion and cross-clamping of the aorta. Contractile reserve was not significantly different between normal dogs and dogs with chronic coronary artery occlusion before and after aortocoronary bypass. Myocardial blood flow during control conditions was homogenously distributed in all three groups studied. The ratio of blood flow to the endocardium and the epicardium was not significantly different from inity. Coronary reserve was determined at peak reactive hyperemia following a 20 second period of coronary artery occlusion, with ongoing norepinephrine infusion. Under these conditions subendocardial fow in normal dogs rose by a factor of 7.9 while subepicardial flow increased 7.4 times. In dogs with chronic occlusion of two coronary arteries the increase of myocardial flow was nonnomogenous; subendocardial flow to areas supplied by a normal coronary artery rose by a factor of 7.0 while subepicardial flow increased 5.7 times control. Subendocardial collateral flow rose by a factor of 2.4 and subepicardial collateral flow increased 3.5 times control. In normal dogs norepinephrine alone did not result in maximal coronary flow but only 57 per cent thereof. Dogs with chronic coronary occlusion, however, required the entire coronary reserve in areas that were supplied by a normal coronary artery, whereas areas supplied by collaterals became ischemic. Opening of an aortocoronary bypass restored normal flow to previously ischemic areas, and reduced the flow to areas supplied by a normal artery. With the bypass open no differences existed between normal dogs and those with two occluded coronary arteries. We conclude that the norepinephrine-stimulated contractile reserve of hearts with chronic coronary occlusion was comparable to that of normal hearts; however, norepinephrine forced these hearts to spend the entire flow reserve of the remaining normal artery while producing ischemia in collateral-dependent areas. The same dose of norepinephrine did not require the entire flow reserve of normal dogs.

Adenosine on myocardial oxygen consumption

1 A 3 min intracoronary infusion of adenosine (50 mug/min) produced a significant decrease in coronary artery perfusion pressure, left ventricular systolic pressure and myocardial O2 consumption in the isolated supported heart preparation of the dog perfused at a constant coronary blood flow. Heart rate was controlled at 150, 190 or 230 beats/minute. 2 Myocardial contractile force and maximal left ventricular dp/dt were not changed by adenosine infusion. 3 The absolute decrease in myocardial O2 consumption was greater at increasing heart rates whereas the decrease in coronary artery perfusion pressure and peak left ventricular systolic pressure were similar. 4 The results suggest that the reduction in myocardial O2 consumption produced by adenosine is not related to coronary vasodilatation or to a negative chronotropic or inotropic action, but may be due to a functional shunting of blood flow from high O2 extracting regions of the myocardium to low O2 extracting ones and/or important effects on myocardial substrate utilization.