2. Endocrines and Populations 227 



indicating that the normal daily secretion of norepinephrine is largely from 

 extra-adrenal chromaffin tissues, whereas the secretion of epinephrine is 

 largely from the adrenal medulla. These facts are particularly pertinent to 

 investigations of the physiologic responses of mammals to sociopsychologic 

 factors. 



The secretion of epinephrine and norepinephrine evidently is controlled 

 by separate hypothalamic centers (Elmadjian et al., 1958). The secretion 

 of norepinephrine apparently is related to an area in the posterior hypothal- 

 amus and that of epinephrine to a lateral area. However, the vasomotor 

 center is in the region of the floor of the fourth ventricle in the medulla 

 oblongata, and it is the most sensitive area relating to the secretion of 

 epinephrine (Elmadjian d o/., 1958). 



In addition to the actions of epinephrine and norepinephrine listed 

 above, these compounds of the sympathico-adrenal system have important 

 activity relationships with other endocrine organs and their hormones. The 

 medullary hormones, thyroid, and pituitary growth and thyrotropic hor- 

 mones have a number of interrelated and interdependent actions. We have 

 already mentioned that growth hormone stimulates adrenal medullary 

 hypertrophy (Moon ct al., 1950, 1951) . Hypertrophy of the medulla with a 

 pronounced increase in its epinephrine content also follows chronic poi- 

 soning of the thyroids of male and female rats with thiouracil (Marine 

 and Bauman, 1945), whereas chronic nicotine poisoning causes a marked 

 medullary hypertrophy mainly owing to an increase in the norepinephrine- 

 containing cells (Eranko et al., 1959). The latter response cannot be 

 elicited in mice or guinea pigs, although the adrenal medulla of the mouse 

 has both epinephrine and norepinephrine-containing cells (Eranko et al., 

 1959). This difference clearly demonstrates the kind of difference one 

 may anticipate between species, even as closely related as arc the rat 

 and mouse (Rattus norvegicus and Mus musculus). The ability of epi- 

 nephrine to mobilize depot fat and produce a rise in unesterified fatty 

 acids in intact animals is thoroughly established (Hartman andBrownell, 

 1949), but its ability to mobilize depot fat, as well as its hyperglycemic 

 action, seems to depend on the integrity of the adrenal cortex and the carbo- 

 hydrate-active corticoids (Levy and Ramey, 1958; DeBodo and Altzuler, 

 1958). These results have led Levy and Ramey (1958) to suggest that the 

 adrenal steroids and epinephrine may act in concert to regulate metabo- 

 lism of fat cells. On the other hand, the ability of epinephrine to mobilize 

 unesterified fatty acids depends on optimal thyroid function, but appar- 

 ently is unrelated to adrenocortical function (Goodman and Knobil, 1959) . 

 The mobilization of fatty acids evidently provides a readily available source 

 of metabolites for the formation of glycogen (Hartman and Brownell, 

 1949) or for direct utilization by the muscles (Fredrickson and Gordon, 

 1958). 



