ENDOCRINOLOGY OF TRANSPORT 



graph of Chapter 4). The apparently multiple effects of insulin in 

 modifying the formation and fate of ATP may easily have a com- 

 mon basis in a reversible action of membrane structures in the syn- 

 thesis and breakdown of ATP. 



Thyroxine 



The uncoupling action of this hormone on oxidative phos- 

 phorvlation does not occur in disrupted mitochondria (Tapley 

 et al., 1955; see Lehninger et al., 1958; Lehninger, 1960a). The in- 

 tact mitochondrion is caused to swell by 10 ~ 8 M thyroxine and 

 by analogous chemical structures that increase the basal metabolic 

 rate. Furthermore, mitochondria isolated from hyperthyroid rats 

 show a much higher spontaneous swelling rate than those from 

 normal animals, whereas mitochondria from hypothyroid rats are 

 very resistant to swelling (Tapley, 1956). The physiologic action 

 of this hormone remains, however, a subject of inquiry. 



Parathyroid hormone 



Calcium has been shown to be concentrated from the mucosal 

 to the serosal compartment of the everted rat small intestine 

 (Schacter and Rosen, 1959). That a higher calcium-ion activity 

 is indeed produced by this transport has been demonstrated using 

 the frog heart, which is responsive only to ionized calcium. The 

 degree of concentration achieved is greater when the rat had previ- 

 ously received parathyroid hormone (Rasmussen, 1959), but an 

 effect of the hormone added directly to the in vitro preparation 

 has not yet been observed. 



Pituitary growth hormone 



Noall and associates (1957) showed that, in the intact rat, the 

 steady-state level of a-aminoisobutyric acid in muscle and several 

 other tissues, relative to the extracellular level, is increased by bovine 

 growth hormone. Kostyo et al. (1959), and Kostyo and Engel 

 (I960) demonstrated an accelerating action of the hormone on the 

 entry of this model amino acid into the isolated rat diaphragm. A 

 prompt acceleration by bovine growth hormone of the passage of 

 an injected dose of a-aminoisobutyric acid from the plasma into 



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