Iodide i -y 



attempted to measure arteriovenous differences in the dog parotid 

 and have found that the extraction of iodide is not complete. 

 Actually complete extraction from whole blood would not be ex- 

 pected in view of the relative slowness with which iodide exchanges 

 between red cells and plasma (Tosteson, 1959), but even allowing 

 for this the values were usually such as to preclude complete 

 plasma extraction. Nevertheless, the iodide clearance probably 

 gives a good index of gland blood flow and to account for such high 

 extractions we must conclude that a high proportion of the blood 

 perfusing the gland comes into contact with the structures in the 

 gland secreting iodide. At least in the dog parotid gland after a 

 rest period the first secreted saliva contains a much higher con- 

 centration of iodide than does subsequently secreted saliva (Burgen 

 and Seeman, 1957; Towbin and Perkins, 1958; Burgen, Terroux 

 and Gonder, 1959). This "rest transient" is discussed in detail in 

 Chapter X. Iodide is also concentrated in the salivary glands in 

 some species, notably in human parotid and submaxillary glands 

 and in mouse and hamster submaxillary glands (Cohen and Myant, 

 1959), but many glands which produce a saliva rich in iodide do 

 not themselves have a concentration of iodide higher than that in 

 the plasma. This could be the case if either intracellular concen- 

 tration of iodide did not occur or if iodide concentration were not 

 a function of all the gland cells but rather of a specific group of 

 cells. The distribution of iodide in the gland has been examined 

 by radioautography of freeze-dried salivary glands in animals given 

 I 131 . By this technique it has been shown that radioiodine is con- 

 centrated by the proximal ducts of the parotid gland in both mice 

 and hamsters (Fig. 8.10). Rats are unable to concentrate iodide in 

 their saliva and in them no such selective accumulation can be 

 seen (Cohen, Logothetopoulos and Myant, 1955; Logotheto- 

 poulos and Myant, 1956). Analysis of the time course of the rest 

 transient mentioned above and of the time of appearance of iodide 

 in the saliva after intra-arterial injection have provided evidence 

 that the ducts are responsible for iodide transfer in the dog parotid 

 as well (Burgen and Seeman, 1957; Burgen, Terroux and Gonder, 

 1959). The rapidity with which saliva iodide concentration in man 

 follows changes in blood iodide content suggests that the same is 

 true in this species (Freinkel and Ingbar, 1953). In the radioauto- 

 graphic studies iodide appears to be concentrated about equally 

 over the duct epithelium and lumen, and where the tissue section 



