CONCENTRATED SOURCES OF ALPHA PARTICLES WITHIN THYROID GLANDS.

One to ten percent of normal bovine thyroids have been shown to contain radioactivity compatible with Ra and/or Th and their radioactive daughters. Radioautographs from thin slices of these thyroids showed concentrated, irregular, anisotropic bodies, 10-60 M* in longest dimension, intensely bombarding thyroidal cells with alpha particles. We have not proven thyroid disease to be caused by radium or thorium in thyroid glands but it is suggested that the natural incidence of some thyroid diseases may be caused by Ra and/or 22STh concentrated within the thyroid. {Endocrinology 91: 1534, 1972) R and thorium have been shown to concentrate in the thyroids of occasional cattle and the concentration in such thyroid glands was 10-20 times greater than in the teeth of the same animals (1). During the past 2 yr we have prepared radioautographs of 13 bovine thyroids which were found to contain gamma spectra of radium and/or thorium. Six of these glands had been preserved by immersion in paraformaldehyde powder in sealed containers for 6 yr before radioautographs were prepared. Materials and Methods Thyroids of cattle slaughtered in Tennessee, Colorado, Japan, Taiwan, New Zealand and Colombia were routinely monitored for I using a 2-inch Nal scintillation crystal. In Colombia, goiter is endemic (2) and 90% of the glands from Colombia were abnormally large; approximately 10% of them contained measurable radioactivity with a long halflife and gamma spectra of radium daughters. Five thyroids with gamma spectra of Ra and Th were previously studied by coincidence spectroscopy (1) and they were proven to contain from 0.8-4.0 pCi of Ra and Th per g of thyroid. The glands with long-lived radioactivity were preserved in 10% formalin, imbedded in paraffin, and sectioned at 510 n in thickness and placed upon microscope slides. They were coated with Kodak NTB2 emulsion (Eastman Kodak Co.), dried and exposed in sealed boxes Received June 13, 1972. in a refrigerator for 3, 8 and 13 months. They were developed in Dektol or D-76 developer (Eastman Kodak Co.), fixed and stained with hematoxylin. The radioautographs were examined by phase contrast, and light microscopy with and without crossed polaroids. Results and Discussion All thyroids with long-lived radioactivity contained numerous anisotropic bodies 10-60 \i in longest dimension, and radioautographs showed these bodies to be surrounded by alpha tracks which extended 20-50 jx into the emulsion (Figs. 1 and 2). Many of the radioactive bodies were located within the colloid, against the follicular cells. Alpha, beta and gamma radiation from the radioactive bodies bombarded surrounding cells and in some areas there was proliferation of cells near the radioactive bodies but the preparations were not adequate to prove the cells to be normal or abnormal. The radioactive bodies in these bovine thyroids may be the major sources of measurable daughters of radium and thorium in the glands. Most of the radioactive bodies were as in Fig. 1, within the colloid but many of the bodies were as in Fig. 2, fixed in position and surrounded by cells. It is possible that in vivo the gaseous intermediate daughters, Rn and Rn, might partially diffuse away from the radioactive bodies and deposit their daughters elsewhere. Ten glands from human beings and 12 from cattle, all with no measurable radioactivity in NOTES AND COMMENTS 1535 FIGS. 1 and 2. Photomicrographs of radioautographs made from the thyroid of a cow slaughtered in Memphis, Tennessee. Photographic emulsion exposed 225 days, alpha tracks are shown as straight dotted lines eminating from radioactive bodies. Length indicator represents SO \i. FIG. 1. Radioactive bodies are within a follicle where a fraction of the alpha radiation is absorbed by follicular cells and the remainder by colloid. the 2-inch scintillation crystal, were processed as controls to eliminate the possibility of artifacts. No alpha tracks were found in the specimens from human subjects after 6-11 months of exposure of the radioautographs. Slides from three of the 12 cattle had 1-3 radium bodies as shown in Fig. 1 except that only 3-6 alpha tracks appeared after 6 months' exposure. It was concluded that radioautographic detection was more sensitive than gamma radiation measurement. Radium is ubiquitous in nature but normally FIG. 2. Radioactive bodies outside of follicles where most of the alpha radiation is absorbed by cells.