IODINE 257 



ing of the thyroid: cattle, 200 /xo; burros, 10 ixc; sheep, 25 nc; pigs, 35 /if- 

 With mice, rats, and chicks a dosage of about 0.5 fic is adequate for assay 

 of the dissected gland. In man, dosages of 1 to 40 fic are used for diag- 

 nostic purposes (see Chap. 5). In a study to determine the nature of 

 plasma iodine, 150 /ic P^^ was injected into a rat that had been raised on a 

 low iodine diet (1-9). The plasma was extracted with butanol, and the 

 extract added to filter-paper strips for preparation of a chromatogram 

 with collidine-water-NHj solvent. Autoradiograms were prepared by 

 exposure of the dried chromatogram to no-screen X-ray film for 5 days. 

 Most of the radioactivity was found in the same position occupied by 

 added thyroxine, as determined by a color test with diazotized sulfanilic 

 acid. 



In a further study, /-thyroxine was labeled with I'^^ to give a specific 

 activity of about 2 fjic/fxg of the compound. Donor rats were given 100 ^g 

 of the thyroxine, and bile samples collected for administration to recip- 

 ient rats (I-IO). Filter-paper chromatograms were prepared, the tissues 

 dissolved in strong alkali, and ahcjuots dried for counting with an end- 

 window tube. Distribution of P^^ in mice was followed by administra- 

 tion of 3 to 20 idc/g body weight (I-ll). The tissues were completely 

 hydrolyzed in 20 per cent NaOH for solution counting of 5 ml. To ascer- 

 tain the age at which the thyroid of the embryo hamster becomes func- 

 tional, 50 to 100 ijlc P^^ was injected intraperitoneally into the gestating 

 hamster at 8 to 15 days after copulation (1-12). In addition to counting, 

 the sectional embryos were exposed to dental X-ray films for 6 to 8 days, 

 and after the autoradiograms were made, the sections were stained in 

 Delafield's hematoxylin and eosin for histological study. Blood, plasma, 

 and "globulin" space of the guinea pig were determined by isotope dilu- 

 tion after intravenous injection of about 3.94 nc of P-^'-labeled rabbit 

 globuHn (1-13). Blood was obtained from the ear with a 20-mm^ Sahli 

 pipette and placed in an ointment tin lined with lens paper. The pipette 

 was washed with 1 : 10,000 heparin two or three times for quantitative 

 transfer. The samples were dried with an infrared lamp and counted 

 with an end-window tube. No self-absorption corrections were necessary. 



The absorption characteristics of iodinated casein in mammals and the 

 identification of some of the metabolites appearing in the blood were 

 studied by use of P^ ^-labeled casein at the following levels: rats, 2 X 10^ 

 counts/min in 0.27 g iodocasein given orally; sheep, 2.8 X 10^ to 5.5 X 

 10^ counts/min in 0.96 to 3.2 g iodocasein administered intravenously, 

 orally, in ventral sac of rumen, small intestine, and caecum (1-14). 

 Standard chemical separations were used for estimation of thyroxine and 

 diiodotyrosine inorganic iodine fractions. The distribution of P^^ in 

 sheep and the physiological manifestations of radiation injury were 

 studied by daily feeding of a drilled food pellet containing 480 fxc P'' 



