HORMONES 289 



due to increased heart rate and contraction of the arteriols (small arter- 

 ies) . The blood pressure falls again rather quickly unless additional 

 doses are given. The hormone also brings about contraction of the iris, 

 relaxation of bronchial muscles, increased salivary secretion, and other 

 effects. These responses, in general, are the same as those caused by 

 stimulation of the sympathetic nerves going to the same tissues or organs. 

 In fact, it appears that epinephrine, or norepinephrine, is necessary for 

 transmission of nerve impulses in the sympathetic (or "adrenergic") 

 nerve system. Some sympathetic nerve cells produce epinephrine, and 

 others, norepinephrine. According to Tainter and Luduena, these hor- 

 inones probably pass through the nerve trunks to the endings, are released 

 when the nerve is stimulated, and act on the particular tissue concerned 

 to produce the effect finally seen. 



Epinephrine also causes a rise in the amounts of glucose and lactic acid 

 in the blood stream and increases the basal metabolic rate (p. 424). 

 Blood sugar is derived from glycogen by the following reactions (see 

 Fig. 13-1): 



1 TT T-,/^ (phosphorvlase) ,11 (phosphogluco-mutase) 



glycogen + H3F04 ' »■ glucose- 1-phosphate *- 



(phosphatase') 



glucose- 6-phosphate > glucose + H3PO4 



It is the first of these steps which is stimulated by epinephrine. Norepine- 

 phrine has only about one-eighth the effect of epinephrine in raising 

 the blood sugar level. 



The secretion of the adrenal medulla is under nervous control and is 

 increased in times of stress or intense emotion (suffocation, rage, fear, 

 etc.). The net result is a general mobilization of the resources of the 

 individual to meet the crisis. Aside from its direct natural functions, 

 epinephrine has also found a number of medical applications, particularly 

 as a vasoconstrictor (blood vessel constrictor), and for relief of the 

 bronchial spasms of asthma and hay fever. Injected together with a 

 local anesthetic such as Novocaine, it contracts small blood vessels and 

 reduces blood flow through the area affected. It thus permits a longer 

 and more intense response from a given dose of the anesthetic. It also 

 has antihistamine action and usually gives relief in a variety of allergic 

 conditions thought to be due to the liberation of a histamine-like substance. 



Histamine is the amine formed by decarboxylation of histidine (p. 321) . 

 Even small doses of it can produce symptoms of allergy. A number of 

 drugs intended to destroy or counteract histamine have been developed. 

 They are called antihistamines, and their effect is called an antihistamine 

 action. Benadryl and Pyribenzamine are two widely used antihistamine 

 drugs: 



