2. Endocrines and Populations 223 



4. Epinephrine and Norepinephrine ; the Hormones of the Aduexal 

 Medulla and Sympathetic Nervous System 



The adrenal medulla and its hormones, epinephrine and norepinephrine, 

 have been the subjects of numerous and ^"oluminous reviews and are also 

 discussed in considerable detail in most good texts of physiology and phar- 

 macology. Therefore, except for a few aspects, a detailed account of these 

 hormones and their physiologic and pharmacologic actions will not be given 

 here. The reviews of the following investigators may be referred to for a 

 more detailed coverage of the subject: Hartman and Brownell, 1949; von 

 Euler, 1951; Hagen and Welch, 1956; Gaddum and Holzbauer, 1957; 

 Ramey and Goldstein, 1957; Elmadjian et al., 1958. 



The adrenal medulla is an integral part of the sympathetic nervous sys- 

 tem. The medulla is homologous with the sympathetic ganglia and is in- 

 nervated by cholinergic preganglionic fibers of the splanchnic sympathetic 

 nerves. Upon stimulation of the sympathetic nervous system, the adrenal 

 medulla discharges norepinephrine and epinephrine into the systemic circu- 

 lation, the proportions of these two compounds varying with the species 

 and with the nature of the stimulus (von Euler, 1951; Hagen and Welch, 

 1956; Gaddum and Holzbauer, 1957; Gray and Beetham, 1957; Elmadjian 

 et al., 1958; Goldfien et al., 1958). Norepinephrine is also secreted by the 

 postganglionic sympathetic nerves and by the extra-adrenal chromaffin 

 tissue of the sympathetic nervous system (von Euler, 1951; Hagen and 

 Welch, 1956). Norepinephrine probably is the neurohumoral transmitter 

 substance of the postganglionic sympathetic nervous system, and appar- 

 ently is released on nervous stimulation at the sympathetic nerve endings 

 (von Euler, 1951 ; Hagen and Welch, 1956; Richardson and Woods, 1959). 

 These two hormones have profound effects on the circulatory system and 

 glucose and fat metabolism, but by and large their effects are short lived, 

 owing to their rapid destruction in the body by the cytochrome oxidase 

 system or by amine oxidases (Bell et al., 1950; Gaddum and Holzbauer, 

 1957). Norepineplirine and epinephrine have a variety of effects over the 

 entire body which are brought about largely by their actions on smooth 

 muscle and which in general parallel the effects of stimulating the sympathe- 

 tic nervous system (Hartman and Brownell, 1949). 



Epinephrine and norepinephrine both have profound pressor effects on 

 the cardiovascular system and on the levels of blood sugar; but epinephrine 

 in general has a greater effect on carbohydrate metabolism and produces a 

 greater hyperglycemic response than norepinephrine, whereas norepineph- 

 rine has a greater pressor effect than epinephrine (Gaddum and Holzbauer, 

 1957). In many ways the actions of these two hormones are similar, but in 

 others they have opposing actions. Norepinephrine in general produces a 



