pyrocatechin derivatives that participate in physiological and biochemical processes in animals and man. The catecholamines include epinephrine, norepinephrine, and dopamine.

Being hormones from the medullary layer of the adrenals and mediators of the nervous system, catecholamines reflect and determine the condition of the sympathetic division of the autonomic nervous system. They play an important role in neurohumoral regulation and neurotrophic functions and take part in the body’s metabolism and adaptive reactions to ensure the constancy of the internal environment and physiological functions (homeostasis). The effects of the catecholamines are the result of their reaction with adrenoreceptors, reactive cellular systems that react specifically with catecholamines. The a-adrenoreceptors are associated mainly with excitation; the /3-adrenoreceptors, with the inhibition of smooth muscles and with the acceleration and intensification of cardiac contractions. Catecholamines are present in blood, organs, tissues, and urine. During physical and mental exertion and in certain diseases (for example, in tumors of the adrenal medulla), the catecholamine content of the blood and urine increases sharply. Catecholamines undergo metabolic conversions (oxidative deamination, O-meth-ylation, quinoid oxidation) that lead to their inactivation or alter their physiological and biochemical properties. When functioning as mediators, the catecholamines are deposited in special granules at the nerve endings.

A number of pharmaceutical agents act on the different stages of catecholamine synthesis, release, deposition, and metabolism. For example, reserpine depletes the catecholamine reserve; par-gyline and iproniazid suppress the oxidative deamination, and Aldomet the synthesis and deposition, of catecholamines; and guanethidine and bretylium prevent the transmission of nervous impulses. These substances are used to intensify or to moderate the activity of the sympathetic nervous system.