BIOLOGICAL TRANSPORT 



+/S 



Figure 30 Schematic representation of the hypothetical action of 

 the antidiuretic hormone. Through electrostatic attractions or hydrogen 

 bonding, the hormone is aligned at the receptor site. A thiol-disulfide 

 exchange reaction follows. This triggers a chain reaction of sulfhydryl- 

 disulfide reactions, which brings about conformational changes in the 

 protein components of the diffusion barrier to permit increased flux of 

 water and certain solutes. The hormone-receptor disulfide bond is 

 ultimately cleaved enzymatically to restore the membrane to its original 

 state. \_From Fong, C. T. O., et al. (1960), Proc. Natl. Acad. Sci. U.S., 46, 

 1273; with permission.'] 



modify migration through the mucosal surface of the cells undoubt- 

 edly has implications for the mode of action. 



An entirely different proposal as to the mode of action of vaso- 

 pressin has been made by Orloff and associates (1962). These au- 

 thors point out that, under suitable conditions of injection, the hor- 

 mone can mimic the action of ACTH in causing hydrocortisone re- 

 lease from the adrenal cortex and can mimic the action of glucagon 

 in causing glucose release from the liver (Hilton et al., 1959; Bergen 

 et al., 1960). Orloff and his associates suggest that both actions are 

 intermediated by adenosine-3',5' cyclic phosphate. This substance, 

 they suggest, may be frequently involved in actions on membranes. 

 The following scheme is proposed: 



vasopressin 



ATP 



cyclic 3',5'-AMP 



i 

 i 

 i 

 i 

 i 

 i 

 •*■ 



permeability 

 change 



98 



theophylline 



-> 5'-AMP 



