Diminished secretion of growth hormone is responsible in part for the decrease of lean body mass, the expansion of adipose-tissue mass, and the thinning of the skin that occur in old age.

The amounts of cortical and trabecular bone mineral mass were measured by means of microdissection and an ashing technique at approximately 2.5 mm intervals along the most distal 12 cm of radii and ulnae from four women aged 21, 43, 63, and 85. The data show that the distributions of mineral mass and percentage of trabecular bone are similar in both bones. At sites in the radius and ulna commonly used in the photon absorptiometric method of bone mineral mass measurement the percentage of trabecular bone varies between 10% and 50%. The percentage of trabecular bone in the most distal 10% of the length of the radius and ulna remains approximately constant with age but the percentage in the segment which lies between 30% and 40% of the length, measured from the styloid process, increases with age.

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H d t h Physics V d . 35 (July) pp. 91-101 P a w o n Press M.. 1978. Printed in Orcat Britain 0 Health Physics Society 00 I7-W78/78/070 1 -00! 3Abstract-The ICRP model, Alkaline Earth Metabolism in Adult Man, predicts that 10% of injected radium-224 atoms decay on bone surface, and that 1.5% decay in bone volume. The model was rerun for all possible values of the size of the bone surface compartment and of its rate constant in an effort to determine the reliability of the bone surface prediction. These runs together with data for 45Ca, "'Ba, and 526Ra in rabbits and dogs lead to lo+ 2% (probable error) as our best estimate for the bone surface fraction of injected '=Ra in man. This estimate corresponds to a time of maximum radium concentration at bone surface in man of 18+6hr, and a preference for radium compared to calcium in the size of the bone surface compartment of between 2 and 3. New measurements of the total surfacelvolume ratio of bone from 10 human skeletons give a preliminary value of 50 cm2/cm3. Assuming 100% retention of thoron and its daughters at bone surface, these input values, together with integrations reported by Mays, give the estimate that an intravenous injection of 1 pCi of 224Ra in a 70 kg standard man with 5 kg of bone results in an average dose to the endosteal cells 0-10 p m from bone surfaces of 1.5rad. Considering all sources of error we believe this estimate is probably good to within a factor of 2.By calculatin the ratio of the endosteal doses for equal average doses to bone for both 224Ra and ' $u relative to 226Ra in man, we give values for what we have called the Relative Distribution Factor (RDF). This factor predicts the relative toxicity of alphaemitting radionuclides in man relative to 226Ra on the assumption that the dose to endosteal cells is the causative factor. The value of RDF('"Rala6Ra) is 20, practically independently of whether endosteal dose is averaged 0-5 p m , 0-10 p m , 0-20 p m , or 0-30pm. The RDF(23%/p6Ra) is about 28 for a surface source of plutonium, and O.% for a volume source of plutonium. The reference for these factors is taken to be a volume source of 226Ra. Since endosteal doses calculated by averaging exactly 0-10 p m from bone surface are somewhat arbitrary for alpha emitters-we don't really know exactly how far from bone surfaces the target cells lie-it is reassuring to find that RDFs for alpha emitters relative to '=Ra are almost independent of distance so long as the cell targets lie within 3 0 p m of the bone surface. Therefore, the RDF with p6Ra as the standard of reference provides a more secure description of the spatial differences between the dose distributions of alpha emitters in bone than does endosteal dose itself.The observed RBE of 224Ra relative to 226Ra for the induction of osteosarcomas-the ratio of average bone doses (226Ra/mRa) for equal incidences-is about 6, a factor of 3 less than the RDF of 20. In other words, by present calculations, 224Ra appears to be a 'Work performed under the auspices of the U.S. Atomic Energy Commissi...

A 133Xenon clearance technique was used io measure blood flow in the capillary bed of non‐inflamed attached gingiva. Measurements were made before and after brushing in a standardized manner. The results show that blood flow through attached gingiva is greater than in published data for skin and increases significantly with brushing. The increases measured, however, are much smaller than those reported for skin under similar stimuli. It is concluded that the high flow within unbrushed attached gingiva may be nearer the maximal possible flow than is the case for skin. The smaller increases measured as a result of brushing the gingival tissues may therefore represent a near maximal microcirculatory response.

Our analysis of data from the beagle project completed at the University of Utah has provided some comparisons that appear to be useful in testing the model proposed by Raabe of effective thresholds for induction of skeletal malignancy by bone-seeking radionuclides in beagles. Raabe's model predicted that cumulative skeletal doses of less than about 0.9 to 1.4 Gy from alpha emitters or 28 to 70 Gy from beta emitters deposited in the skeleton require a long enough time for bone cancer expression that the dog's natural lifespan would be exceeded before the tumor appeared. Results from the Utah beagle project seem to confirm these projections for 226Ra, 228Ra and, perhaps, for 90Sr. The lowest doses at which malignant bone tumors were observed in animals injected with these radium isotopes were about 0.9 Gy (226Ra) and 3 Gy (228Ra). For the beta emitter, 90Sr, the lowest doses at which bone tumors were seen were about 18, 50, and 70 Gy with an expectation for naturally occurring tumor of about one. Twenty-six of the two hundred and thirty-three Utah beagles given monomeric 239Pu that developed skeletal malignancies had doses between 0.02 and 0.51 Gy (80 of these dogs had skeletal doses of less than 0.9 Gy). Three dogs of 54 given 241Am with doses lower than 0.9 Gy had bone tumors at 0.23, 0.56, and 0.88 Gy with the expectation of about one naturally occurring case. For 25 animals injected with 228Th at skeletal doses below 0.9 Gy, one bone tumor dog had a dose of about 0.4 Gy, and the expectation of a dog with natural tumor among the group was only about 0.38. Five beagles of 74 given 224Ra with resulting doses of less than 0.9 Gy died with skeletal malignancy at 0.32 Gy or less with an expectation for non 224Ra induced tumor of about one. It appears that Raabe's proposal might be confirmed for some but not all of the radionuclides used in the Utah studies. Models presented in earlier papers by Raabe provide results that are somewhat different from his recent abstract and compare more favorably with those cited herein for Utah dogs. Re-examination of our data for these analyses has suggested a novel concept for calculation of carcinogenic dose to endosteal bone surfaces.

Ultramicrochemical methods were used to assay lactic dehydrogenase, (L.D.H.) malic dehydrogenase (M.D.H.) and glucose‐6‐phosphate dehydrogenase (G‐6‐P.D.H.) in biopsy specimens obtained from palatal mucosa and gingiva of young human volunteers. Half the specimens examined came from individuals who had used a chlorhexidine containing mouthrinse for 18 months and the other half from individuals using a placebo mouthrinse. There were no statistically significant differences in enzyme activity between the two groups. It is concluded that the activities of the glycolytic processes investigated, confirm the lack of any chronic inflammatory process in the chlorhexidine exposed tissue.