Effects of hydrocortisone, phenoxybenzamine and propranolol on the blood plasma levels of adrenaline and noradrenaline during hemorrhagic hypotension in the dog.

The adrenergic aspects of the mechanism(s) of the vasodilating action of phenoxybenzamine and massive doses of hydrocortisone were studied in anesthetized dogs subjected to controlled hemorrhagic shock. During the predrug hypotension period with decreased cardiac output and heart rate, the plasma adrenaline and noradrenaline levels were both increased. Phenoxybenzamine injected alone augmented the cardiac output and heart rate and reduced the plasma adrenaline without changing the plasma noradrenaline concentration. However, if the adrenergic alpha-receptor blocker was administered in combination with massive doses of hydrocortisone, the degree of vasodilation increased further with a concomitant increase in the concentrations of the two plasma catecholamines. Thus there seems to be no clear-cut relationship between hemodynamic changes and plasma catecholamines. The present findings illustrate the extreme complexity of plasma catecholamine kinetics during hypovolemic shock.