ENDOCRINOLOGY OF TRANSPORT 



of separate enzyme systems, have come to be recognized, and the 

 conception has gained strength that endocrinologic effects may fre- 

 quently concern barriers and access. 



Rudolph Peters has voiced a related idea, that hormones act 

 on the "cytoskeleton" of the cell (1956). He suggests that a hor- 

 mone may, by entering the surface of the cell, change anatomic 

 orientations not only in the plasma membrane but in other structural 

 elements throughout the cell so that several enzymatic reactions 

 are modified simultaneously. Hechter and Lester (1960) have 

 voiced similar views. 



The present discussion, which continues earlier comment from 

 this laboratory (Christensen, 1948, see also Appendix 2; Noall 

 et al., 1957), summarizes the instances in which hormones appear 

 to modify transport processes. 



Aldosterone 



Of the several steroids that modify alkali metal transport, 

 aldosterone is outstanding in its potency, particularly on the renal 

 tubule. It has so distinct an action to intensify the exchange of 

 sodium ion from the fluid passing through the lumen, for potassium 

 ion from the plasma, that the behavior may serve as a sensitive 

 assay for the hormone. At the same time, the distribution of the 

 alkali metal ions between the cells and the extracellular fluid is recog- 

 nized to be disturbed in adrenal cortical deficiency, and to be modi- 

 fied by mineralcorticoid therapy. Aldosterone has also been found 

 to modify sodium-ion transport by the frog skin, by the salivary 

 gland, and by the sweat glands. 



Estrogens 



In 1957 Noall and associates showed that the administration 

 of a microgram of /3-estradiol to the weanling female rat caused a 

 tripling of the level of a-aminoisobutyric acid in the uterus, this 

 model amino acid having been permitted in advance to distribute 

 itself throughout the animal. Noall and Allen (1961) later showed 

 that estradiol can intensify the accumulation of a-aminoisobutyric 

 acid by the uterus of the rabbit in a 30-minute interval. We may 

 perhaps rationalize that such an action applied to ordinary amino 

 acids permits this organ to accelerate its protein synthesis and 



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